synthesis of acetylenes, allenes and cumulenes || base-catalysed isomerisations of acetylenic...

[13.1.2004–9:55pm] [319–340] [Page No. 319]

E:/Archive files/4188-Brandsma/Printer-Files/4188-Chapter-17.3d

17Base-Catalysed Isomerisations of

Acetylenic Compounds

17.1 INTRODUCTION

Interaction between an acetylenic compound and a catalytic amount of a base

can give rise to isomerisation to an unsaturated system with the same number

of p-electrons. The result is often a (pseudo-) equilibrium mixture of the start-

ing compound and isomeric acetylenes or allenes. The composition of the

mixture is determined by the relative thermodynamic stabilities of the isomers.

Under more forcing conditions a conjugated diene or polyene is formed, pro-

vided that the carbon chain is sufficiently long, while in some cases cyclic

compounds are the end products. Since it is, in general, very difficult to sepa-

rate the isomeric compounds, the synthetic importance of the base-catalysed

isomerisations is restricted to conversions that afford predominantly one

product. The ratio of the isomers in the equilibrium mixture may vary

strongly with the substituents. Reaction of N,N-diethyl-2-propyn-1-amine,

HC�CCH2NEt2, with t-BuOK in DMSO gives an equilibrium mixture [1] of

�80% of N,N-diethyl-1-propyn-1-amine MeC�CNEt2 and �20% of N,N-

diethyl-1-allenamine, H2C¼C¼CHNEt2. Under similar conditions the

dimethylamino compound, HC�CCH2NMe2, is converted into a mixture con-

sisting of �10% of N,N-dimethyl-1-propyn-1-amine, MeC�CNMe2 and �90

of N,N-dimethyl-1-allenamine [2], H2C¼C¼CHNMe2. 1-Propargylpyrrole,

HC�CCH2-1-pyrrolyl, prepared in situ from pyrrole, potassium hydroxide

and propargyl chloride in dimethylsulphoxide, isomerises completely to 1-alle-

nylpyrrole under the reaction conditions [6]. The base-catalysed isomerisation

of 3-alkoxy-1-propynes, HC�CCH2OR, to alkoxyallenes, H2C¼C¼CHOR,

can be easily brought approximately by warming with solid t-BuOK [3].

Attempts at further conversion into 1-alkoxy-1-propynes, MeC�COR, have

resulted in decomposition [1]. 2-Propynyl sulphides, HC�CCH2SR (R¼ alkyl

or aryl), can be completely converted into 1-propynyl sulphides, MeC�CSR,

under mild conditions (NaOEt in liquid ammonia [4] or in ethanol [5]).

319

[13.1.2004–9:55pm] [319–340] [Page No. 320]


Compounds with the structure HC�CCH2CH2R, in which R may represent

alkyl, aryl or a variety of other groups, isomerise smoothly to the 2-alkyne

systems, MeC�CCH2R, upon treatment with t-BuOK in DMSO at 20 �C or

slightly elevated temperatures [1].

In addition to the reactions mentioned, many other isomerisations of acety-

lenic compounds with a conjugated or non-conjugated unsaturated system

have been carried out. The experimental procedures in this chapter are a selec-

tion of conversions that, in our opinion, are useful from a preparative point of

view. A number of base-catalysed isomerisations are summarised in Table 17.1.

The isomerisation conditions in the procedures described below result from

an extensive experience in this field.

So-called contrathermodynamic isomerisations, brought about by treatment

of a substrate with equivalent amounts of a very strongly basic reagent and

subsequent protonation of the alkali metal intermediate, are treated in

Chapter 3.

17.2 EXPERIMENTAL SECTION

17.2.1 Isomerisation of 1-alkynes to 2-alkynes

Scale: 0.30 molar; Apparatus: 500-ml round-bottomed two-necked flask with

stopper and thermometer-outlet combination; stirring is carried out magneti-

cally; addition by syringe or – in the case of 1-butyne – by pouring the cold

liquefied gas into the flask.

1-Alkynes are smoothly converted into 2-alkynes under the influence of a

catalytic amount of t-BuOK in DMSO at temperatures between 20 and

40 �C. Using �10 mol% of base and concentrations of the alkyne between 1

and 5 mol/litre of DMSO, the conversion is complete within 30 min. From

the modest enthalpy difference of 1- and 2-alkynes (roughly 5 kcal/mol) and

the heat capacity of the solvent and alkyne (�0.5 cal/ �C/g), a rough estimate

can be made of the amount of heat evolved in the isomerisation of 0.5 mol of a

1-alkyne to the 2-alkyne in �150 ml of DMSO. This leads to the conclusion

that the 1-alkyne can be added over a short period. Cooling in a water bath

at 10–15 �C will be sufficient to keep the temperature of the solution between

25 and 40 �C. In the case of the volatile 1- and 2-butyne, the temperature

should not be allowed to rise above 30 �C. There is little risk of a further iso-

merisation into a conjugated diene in this temperature range.

320 17. ISOMERISATIONS OF ACETYLENIC COMPOUNDS

[13.1.2004–9:55pm] [319–340] [Page No. 321]


Table 17.1

Base-catalysed isomerisations of acetylenic compoundsa

Acetylenic compound Reaction conditionsb Isomerisation product

HC�CCH2Alky1 t-BuOK, DMSO, 30 MeC�CAlkyl

HC�C(CH2)9OH t-BuOK, DMSO, 30 MeC�C(CH2)8OH

HC�CCH2NMe2 t-BuOK, DMSO, 30c H2C¼C¼CHNMe2HC�CCH2NEt2 t-BuOK, DMSO, 50–55d MeC�CNEt2HC�CCH2N-morpholyl t-BuOK, THF, 40–45 H2C¼C¼CHN-morpholyl

Me2NCH2C�CCH2OMe t-BuOK � t-BuOH, THF, 40 Me2NCH¼C¼CHCH2OMe

HC�CCH2N-pyrrolyl KOH, DMSO, 45e H2C¼C¼CHN-pyrrolyl

HC�CCH2N-imidazolyl t-BuOK, liq. NH3, �33 H2C¼C¼CHN-imidazolyl

HC�CCH2N-pyrazolyl t-BuOK,1iq. NH3, �33 H2C¼C¼CHN-pyrazolyl

HC�CCH2OMe t-BuOK, DMSO,

30! 55fH2C¼C¼CHOMe

HC�CCH2O-t-Bu t-BuOK, no solvent, 55 H2C¼C¼CHO-t-Bu

HC�CCH2OCH(Me)OEt t-BuOK, DMSO, 30–35f H2C¼C¼CHOCH(Me)OEt

EtOCH2C�CCH2OEt t-BuOK, liq. NH3, �33 EtOCH¼C¼CHCH2OEt

EtOCH(Me)C�CCH2OMe t-BuOK, liq. NH3, �33 EtOCH(Me)CH¼C¼CHOMe

EtOCH2C�CCH(OEt)2 t-BuOK, DMSO, 30–35 EtOCH¼C¼CHCH(OEt)2n-PrC�CCH(OEt)2 t-BuOK, DMSO, rt! 40 EtC�CCH2CH(OEt)2MeC�CCH(SEt)2 NaOEt, liq. NH3,

�33gMeCH¼C¼C(SEt)2

HC�CCH2SEt NaOEt, liq. NH3, �33 MeC�CSEt

HC�CCH2CH¼CH2 NaOH, EtOH, 35 H2C¼C¼CHCH¼CH2

HC�CCH2C�CH PhOLi, MeOH, rt! 50 H2C¼C¼CHC�CH

HC�CCH¼CHCH2R t-BuOK, DMSO,

rt, 1 min

MeC�CCH¼CHR

H2C¼C(Me)C�CCH2OMe t-BuOK, HMPT, 25 H2C¼C(Me)CH¼C¼CHOMe

H2C¼CHC�CCH2NEt2 t-BuOK, DMSO, 30–35h MeCH¼CHC�CNEt2H2C¼C(Me)C�CCH2NEt2 t-BuOK, DMSO, 30–35 Me2C¼CHC�CNEt2HC�CC�CCH2NEt2 t-BuOK � t-BuOH,

HMPT, 10

MeC�CC�CNEt2i

HC�CCH2C(¼O)Et NaHCO3, H2O, rt H2C¼C¼CHC(¼O)Et

HC�CCH¼CHCH2C�N K2CO3, H2O, EtOH, 60–80 H2C¼C¼CHCH¼CHC�N

aAll reactions were carried out in the author’s laboratory.bTemperatures in �C.c�10% MeC�CNMe2 present in the equilibrium mixture.d�20% H2C¼C¼CHNEt2 present in equilibrium mixture.

eThe acetylenic isomer is formed in situ from pyrrole, KOH and propargyl chloride [6].fDMSO is added in relatively small amounts [1].gRef. 8.h�15% of N,N-Diethyl-l-penten-3-yn-l-amine, MeC�CCH¼CHNEt2, is formed [7]. The two

isomeric products can be separated by distillation.iUsing DMSO, yields are much lower [1].

17.2 EXPERIMENTAL SECTION 321

[13.1.2004–9:55pm] [319–340] [Page No. 322]


17.2.1.1 Procedure

Dry DMSO (100 ml) and t-BuOK (3 g) are placed in the flask. Stirring is

started and the solution is brought at a temperature of �20 �C. Liquefied

1-butyne (0.30 mol, Chapter 10, exp. 10.2.3) or 1-hexyne (0.30 mol, Chapter

4, exp. 4.5.8) is added in portions of �5 g with intervals of 3 to 5 min, while

keeping the temperature of the mixture between 25 and 30 �C (bath at �15 �C).

After an additional 30-min period of stirring at �30 �C the 2-alkynes are iso-

lated. In the case of 2-butyne the flask is connected (via a vacuum tube) to a

trap cooled in a bath with liquid nitrogen. The connection is made in such a

way that during the evacuation with the water aspirator, the vapour of

2-butyne enters the large annular space of the trap: in this way, clogging

being avoided. During the evacuation, the temperature of the bath is gradually

raised to 50 �C. Air is then admitted to the system and the solid 2-butyne is

allowed to melt. Subsequent distillation at atmospheric pressure using a short

Vigreux column and a receiver, cooled below 0 �C gives pure 2-butyne, bp

�27 �C, in >75% yield. For the isolation of 2-hexyne, the reaction flask is

equipped for a vacuum distillation: 40-cm Vigreux column, condenser and

receiver cooled in a bath at �70 �C (Figure 1.10). The system is evacuated

(water aspirator) and the flask gradually heated, until the DMSO begins to

reflux in the column. Redistillation of the contents of the receiver at atmo-

spheric pressure gives 2-hexyne, bp 85 �C, in �90% yield. The IR spectrum

shows the absence of 1-hexyne.

2-Heptyne and 2-octyne can be isolated in a similar way. In the case of less

volatile 2-alkynes it is more convenient to dilute the reaction mixture with

water (500 ml) and to extract with pentane.

17.2.2 Isomerisation of 10-undecyn-1-ol to 9-undecyn-1-ol

Scale: 0.10 molar; Apparatus: 250-ml round-bottomed flask and thermometer;

manual swirling

17.2.2.1 Procedure

10-Undecyn-1-ol (0.10 mol) is added in one portion to a solution of 2 g of

t-BuOK in 200 ml of dry DMSO. The temperature rises from 20 to �30 �C

within 1 to 2 min and a white precipitate is formed. The mixture is subse-

quently heated to 80 �C and held at this temperature for 2 min. The precipitate


[13.1.2004–9:55pm] [319–340] [Page No. 323]


dissolves completely. After cooling to rt, the solution is poured into 500 ml

of water and six extractions with a mixture (1:1) of Et2O and pentane are

carried out. The combined organic solutions are washed twice with water

and subsequently dried over MgSO4, after which the solvent is removed

under reduced pressure. Distillation of the remaining liquid through a short

Vigreux column gives 9-undecyn-1-ol, bp 100 �C/15 Torr, in >90% yield.

17.2.3 Isomerisation of N,N-diethyl-2-propyn-1-amineto N,N-diethyl-1-propyn-1-amine


manual swirling

Treatment of a propargylic tertiary amine, HC�CCH2NR2, with a catalytic

amount of a basic reagent under suitable conditions generally affords an equi-

librium mixture of the allenic amine, H2C¼C¼CHNR2, and the 1-propynyl-

amine, MeC�CNR2. This cannot be separated into the components by

distillation because of the small difference in boiling points. There is, however,

a considerable difference in thermal stability of the yneamines and allenic

amines. If a mixture of N,N-diethyl-1-propyn-1-amine, MeC�CNEt2, and

N,N-diethyl-1-allenamine, H2C¼C¼CHNEt2, is heated for approximately half

an hour at a temperature above 100 �C, all allenic amine has dimerised. The

yneamine survives this treatment and can be obtained in a good yield by

vacuum distillation. Unfortunately, there are only a few cases in which the ynea-

mine is the main component in the equilibrium mixture. Amines, HC�

CCH2NR2, having one or both groups R ¼ Aryl give the yneamines in high

yields.

17.2.3.1 Procedure

N,N-Diethyl-2-propyn-1-amine (0.30 mol, Chapter 20, exp. 20.2.2) is added in

one portion to a solution of 5 g of t-BuOK in 50 ml of dry DMSO. The

temperature rises in a few minutes to above 45 �C but is kept between 50

and 55 �C by occasional cooling (with manual swirling) in a water bath at

�10 �C. After 30 min the flask is equipped for a vacuum distillation (water-

aspirator pressure, 40-cm Vigreux column, condenser and single receiver,

cooled in a bath at �10 �C, Figure 1.10) and the products are quickly distilled


[13.1.2004–9:55pm] [319–340] [Page No. 324]


off from the dark solution. The distillation is stopped after a few millilitres of

DMSO have passed over (bp �80 �C/15 Torr). The distillate is heated (under

N2) for 30 min in a bath at 120 �C. After cooling to below 30 �C, the yneamine

is distilled through an efficient column and collected in a single receiver, cooled

in a bath at 0 �C (Figure 1.10). N,N-Diethyl-1-propyn-1-amine, bp 27 �C/

12 Torr, is obtained in �75% yield. The residue, a mixture of DMSO and

the dimer of the allenic amine, is discarded. If the compound is stored in a well-

closed and dry bottle, no deterioration occurs at rt.

17.2.4 N,N-Dimethyl-1-allenamine from N,N-dimethyl-2-propyn-1-amine


manual swirling

17.2.4.1 Procedure

A clear solution of 10 mmol of t-BuOK and 10 mmol of t-BuOH in 10 ml

of dry DMSO is prepared by warming the mixture at 50 �C. The solution is

then cooled to 17 �C and added to 5.0 g of N,N-dimethyl-2-propyn-1-amine

(Chapter 20, exp. 20.2.3), in the 100-ml flask. The air in the flask is quickly

replaced by inert gas and the mixture is kept at 23 �C for 10 min (occasional

cooling in a bath of 15 �C may be necessary). During this period the flask is

occasionally swirled by hand. The flask is then connected to a distillation

apparatus (see Figure 1.10), consisting of a 30-cm Vigreux column, condenser

and receiver, cooled at �78 �C. Between the receiver and the water aspirator is

placed a tube filled with KOH pellets. The system is evacuated and the dis-

tillation flask gradually warmed at �80 �C. After this operation nitrogen

is admitted. The receiver contains reasonably pure (�90–95%) N,N-dimethyl-

1-allenamine, yield 85–90%. The NMR spectrum indicates the presence of

5–10% ofN,N-dimethyl-1-propyn-1-amine, MeC�CNMe2 (Note). The product

can be stored under pure nitrogen at �25 �C for at least 24 h.

The equilibrium mixture consists of �20% of MeC�CNMe2 and �80% of

H2C¼C¼CHNMe2. The isomerisation method is therefore unsuitable for the

preparation of the yneamine. In the case of the isomerisation of N,N-diethyl-

2-propyn-1-amine, HC�CCH2NEt2, the equilibrium ratio, allenic amine:ynea-

mine, is �1:4 (cf. exp. 17.2.3).


[13.1.2004–9:55pm] [319–340] [Page No. 325]


Note

All operations of the isolation procedure must be carried out without delay.

The distillation apparatus must be made perfectly dry, as allenic amines are

extremely water-sensitive.

17.2.5 1-(1,2-Propadienyl)morpholine from 4-(2-propynyl)morpholine

Scale: 0.10 molar; Apparatus: 200-ml round-bottomed, three-necked flask pro-

vided with a gas inlet, a thermometer and a gas outlet; magnetic stirring

17.2.5.1 Procedure

In the flask is placed 0.10 mol of the 4-(2-propynyl)morpholine (cf. Chapter 20,

exp. 20.2.2). The air in the flask is replaced by nitrogen and a solution of

10 mmol of t-BuOK in 10 ml of THF is added. The mixture is warmed at

�40 �C. A weakly exothermic reaction is observed and the temperature rises to

�45 �C. After 1–2 min the gel originally present (presumably the potassiated

acetylenic amine) has disappeared almost completely and a brown solution has

formed. The refractive index of the solution (Note 1) is measured after intervals

of �2 min. After the maximum value (nD �1.464) has been reached, heating at

40 �C is continued for another 2 min. t-Butylalcohol (10 mmol) is then added

(Note 2) and the mixture is cooled to rt. The THF is removed in a water-

aspirator vacuum and the residue is distilled (bp 30–40 �C) in a high vacuum

(pressure < 0.5 Torr), the (single) receiver being cooled at 0 �C (Figure 1.10).

Towards the end of the distillation the temperature of the heating bath is

increased to 60–70 �C in order to minimise the hold-up. The yield of 1-(1,2-

propadienyl)morpholine is �85%. The NMR spectrum indicates the presence

of �4% of 4-(1-propynyl)morpholine, MeC�C-Morpholine. The product

rapidly turns yellow upon exposure to the air and polymerises at rt within a

few hours.

A similar procedure with 1-(2-propynyl)piperidine (reaction temperature

45–55 �C) leads to a mixture of 92% of the 1-(1,2-propadienyl)piperidine and

8% of the 1-(1-propynyl)piperidine. During the high-vacuum distillation the

receiver is cooled at –30 �C. The product mixture, bp 30 �C/0.5 Torr, is

obtained in a yield of �80%.


[13.1.2004–9:55pm] [319–340] [Page No. 326]


The equilibrium mixture obtained in this isomerisation under the influence

of t-BuOK in DMSO consists of �70% of allenic and 30% of yneamine.

Base-catalysed isomerisation is therefore not a suitable method to prepare

the 1-(1-propynyl)piperidine.

Notes

1. A small sample is taken by means of a Pasteur pipette and the liquid is

placed on the prism. Care should be taken that no evaporation of THF

takes place as this will result in measuring of a too high refractive index.

2. Conversion into 1-(1-propynyl)morpholine is repressed by the addition of

t-BuOH, which forms the less active 1:1 complex with t-BuOK. If the

isomerisation with t-BuOK is carried out in DMSO, an equilibrium mix-

ture of �80% of the allenic amine and 20% of the yneamine is formed

after 1–2 min at 30 �C.

17.2.6 Isomerisation of N,N-diethyl-4-penten-2-yn-1-amine toN,N-diethyl-3-penten-1-yn-1-amine

Scale: 0.10 molar; Apparatus: 500-ml round-bottomed flask and thermometer

(manual swirling)

The conditions for the base-catalysed isomerisation of N,N-diethyl-4-penten-

2-yn-1-amine, H2C¼CHC�CCH2NEt2, are similar to those applied in

exp. 17.2.3. The work-up cannot be carried out in the same way, because the

bp of the product is too close to that of DMSO. An aqueous work-up seems

risky, since enyne amines have shown to be water-sensitive [1]. The somewhat

peculiar manner in which the product is isolated is based on the fact that

DMSO is slightly soluble in the non-polar pentane. Extraction with this solvent

alone presumably would be not very effective, therefore a 1:1 mixture of pen-

tane and Et2O is used. The small amount of DMSO, which is co-extracted, can

be easily removed by strongly cooling the extract, during which operation the

DMSO crystallises out.

Interestingly, the isomerisation with t-BuOK also gives a small amount of

the amine with the reversed order of the double and triple bond. Its boiling


[13.1.2004–9:55pm] [319–340] [Page No. 327]


point is by 20 to 30 �C higher than that of the predominant product and careful

fractional distillation results in a satisfactory separation of these isomers.

17.2.6.1 Procedure

N,N-Diethyl-4-penten-2-yn-1-amine (0.10 mol, prepared by Mannich reaction

of vinylacetylene, Chapter 13) is added in one portion to a solution of 3 g of

t-BuOK in 45 ml of dry DMSO. The temperature (initially rt) rises within 1 to

2 min to 35 �C, but is kept between 30 and 35 �C by occasional cooling (with

manual swirling) in a water bath at 10 �C. After 30 min the brown reaction

mixture is extracted eight times with a 1:1 mixture of Et2O and pentane (1� 70

ml, 7� 40 ml). The combined extracts are cooled to �80 �C (with continuous

swirling). Fifteen minutes after this temperature has been reached, the cold

mixture is quickly filtered on a sintered-glass funnel (with suction) and the

DMSO on the filter rinsed with a very limited amount of the cold (�80 �C)

Et2O–pentane mixture. After concentration of the extract in vacuo, the remain-

ing liquid is carefully fractionated through an efficient column to give N,N-

diethyl-3-penten-1-yn-1-amine, MeCH¼CHC�CNEt2 ((E):(Z) �70:30), bp

70–75 �C/12 Torr, in �80% yield. The small brown residue consists mainly

of N,N-diethyl-1-penten-3-yn-1-amine, MeC�CCH¼CHNEt2.

N,N-Diethyl-4-methyl-4-penten-2-yn-1-amine, H2C¼C(Me)C�CCH2NEt2,

bp 70 �C/12 Torr, is converted by a similar procedure into N,N-diethyl-

4-methyl-3-penten-1-yn-1-amine, (Me)2C¼CHC�CNEt2, bp 90 �C/12 Torr,

with an excellent yield.

Amines with a longer carbon chain, e.g. N,N-dialkyl-4-hexen-2-yn-1-amine,

MeCH¼CHC�CCH2NR2, give 1,3,5-trienylamines, e.g. N,N-dialkyl-1,3,5-

hexatrien-1-amine, H2C¼CHCH¼CHCH¼CHNR2, under the isomerisation

conditions described above [7].

17.2.7 N,N-diethyl-1,3-pentadiyn-1-amine fromN,N-diethyl-2,4-pentadiyn-1-amine

Scale: 0.20 molar; Apparatus: Figure 1.1, 250 ml, addition by syringe

When N,N-diethyl-2,4-pentadiyn-1-amine, HC�CC�CCH2NEt2, is sub-

jected to the isomerisation conditions of exp. 17.2.4, a vigorous reaction

takes place and a very dark solution is formed from which only tarry products

can be isolated. A moderate yield of N,N-diethyl-1,3-pentadiyn-1-amine,


[13.1.2004–9:55pm] [319–340] [Page No. 328]


MeC�CC�CNEt2, is obtained, when the basic catalyst is ‘poisoned’ by addi-

tion of t-butyl alcohol (ratio t-BuOK/t-BuOH �1:3 by weight). Replacement

of DMSO by HMPT, however, gives good results, provided that during the

isomerisation the temperature is carefully maintained around 10 �C, and the

concentration of the base is not too high. Since HMPT and pentane or Et2O

are completely mixable, a ‘dry’ extraction procedure as described in

exp. 17.2.4 cannot be applied. Fortunately, the diyne amine appears to be

reasonably stable at pH>9 in water at ambient temperature, so that the

compound can be isolated by the usual extraction procedure.

17.2.7.1 Procedure

(Note) Dry HMPT (40 ml) is placed in the flask. A solution of 1 g of t-BuOK

and 3 g of t-BuOH in 5 ml of HMPT is added and the mixture is cooled to 7 �C

(ice-water bath). A mixture of 0.10 mol of N,N-diethyl-2,4-pentadiyn-1-amine,

(Chapter 3, exp. 3.9.33) and 15 ml of dry HMPT, pre-cooled to �5 �C,

is added in 5 equal portions with intervals of �3 min. The temperature of

the dark mixture is maintained between 8 and 12 �C (occasional cooling).

Ten minutes after this addition, a same amount of the solution of the basic

catalyst in HMPT is added and stirring at 10 �C is continued for an additional

10 min. The very dark solution is then poured into 300 ml of ice water and

seven extractions with a 1:1 mixture of Et2O and pentane are carried out as

quickly as possible. The combined solutions are washed twice with ice water

and dried over K2CO3. The liquid remaining after concentration of the solu-

tion in vacuo, is distilled through a short Vigreux column and the distillate

collected in a single receiver cooled in a bath at 0 �C (Figure 1.10). N,N-

Diethyl-1,3-pentadiyn-1-amine, bp�50 �C/0.1 Torr, is obtained in�75% yield.

Note

Possibly, good results are obtained also when using t-BuOK in DMSO,

provided that more than one equivalent of t-butyl alcohol is used to ‘tame’

this base.

17.2.8 Methoxyallene from 3-methoxy-1-propyne

Scale: 1.0 molar; Apparatus: 500-ml two-necked, round-bottomed flask,

provided with a reflux condenser and a thermometer


[13.1.2004–9:55pm] [319–340] [Page No. 329]


17.2.8.1 Procedure

In the flask is placed 1.0 mol of dry freshly distilled 3-methoxy-1-propyne

(Chapter 20, exp. 20.6.1). A solution of 5 g of t-BuOK in 35 ml of DMSO is

added with manual swirling. The temperature of the mixture gradually rises

from 25 �C and after about half an hour a gentle reflux starts. The reaction may

be followed by taking small samples of the reaction mixture at intervals of

�10 min and determining the refractive index. After refluxing has subsided, the

mixture is heated for an additional 30 min in a bath at �70 �C (the maximum

value of nD is �1.427). The flask is cooled to rt and equipped for a distilla-

tion: 30-cm Vigreux column, condenser and receiver. Most of methoxyallene is

distilled off at 760 Torr, care being taken that the temperature of the

heating bath remains below 90 �C. A small amount of allenic ether may be

obtained by evacuation (water-aspirator pressure, receiver cooled in a bath at

�70 �C, Figure 1.10). Pure methoxyallene, bp 52 �C/760 Torr, is obtained in

>85% yield.

17.2.9 t-Butoxyallene from 3-t-butoxy-1-propyne

Scale: 0.50 molar; Apparatus: Figure 1.1, 250 ml, no dropping funnel is used

17.2.9.1 Procedure

In the flask are placed 0.50 mol of freshly distilled and dry (Note 1) 3-(t-

butoxy)-1-propyne (Chapter 20, exp. 20.6.8) and 4 g of powdered t-BuOK.

The mixture is warmed to 54 �C and is kept at this temperature (Note 2) by

occasional cooling or warming until the refractive index (nD) has increased to

1.444 (�70 min, Note 3). The flask is then connected to a 40-cm Vigreux

column, condenser and receiver, cooled at �75 �C (Figure 1.10). A few boiling

stones are added and most of the liquid is distilled at 15–20 Torr. The bath

temperature is gradually increased to �60 �C. When the distillation has

stopped, nitrogen is admitted and the receiver is replaced with an empty one.

The last traces of the allenic ether are subsequently distilled off from the brown

mass at 0.5 Torr or lower pressure, while the flask is warmed in a bath at 50 �C

and the receiver is cooled at �75 �C (Figure 1.10). The yield of tert-butoxyal-

lene is at least 90%.


[13.1.2004–9:55pm] [319–340] [Page No. 330]


Notes

1. If not kept under nitrogen in well closed bottles, 3-(t-butoxy)-1-propyne

is gradually converted into 3-(t-butoxy)-1-propynyl hydroperoxide,

HC�CCH(OOH)O-t-Bu, even during storage at �20 �C. Small amounts

of this peroxide as well as moisture will lead to inactivation of the base. As

a result, the isomerisation is very slow or does not take place. The presence

of hydroperoxide appears from an increase of the nD and from a KI test:

brown colour after shaking a small sample with an aqueous solution of KI.

This colour disappears if shaking is continued for some minutes. The

impure 3-(t-butoxy)-1-propyne can be freed from hydroperoxide by

adding some paraffin oil and subsequently distilling the product at <1

Torr, using a receiver cooled at �70 �C (Figure 1.10) and keeping the bath

temperature below 30 �C.

2. Especially at temperatures higher than 60 �C further conversion of the

allenic ether to 1-(t-butoxy)-1-propyne, MeC�CO-t-Bu, takes place. This

ether splits off isobutene under these conditions and the resulting

ketene. 1-propen-1-one, MeCH¼C¼O, reacts with the allenic ether and

the 1-propynyl ether. The yield of t-butoxyallene is then much lower.

3. Although the nD of the pure allenic ether at 20 �C is 1.4418, the final value

for the reaction mixture is higher, since the t-BuOK partly dissolves in the

allenic ether.

17.2.10 1-Ethoxyethoxyallene starting from propargylalcohol and ethoxyethene

Scale: 1.0 molar; Apparatus: Figure 1.1, 500 ml

17.2.10.1 Procedure

In the flask is placed 100 g of freshly distilled ethyl vinyl ether. After cooling

to –25 �C, a solution of 100 mg of p-toluenesulphonic acid in 5 ml of THF

is added, immediately followed by �5 ml of the total amount of 1.0 mol of

freshly distilled (bp �50 �C in a partial vacuum) propargyl alcohol. After the

evolution of heat (rising of the temperature by several �C) has ceased, the


[13.1.2004–9:55pm] [319–340] [Page No. 331]


remainder of the alcohol is added in 5-ml portions with intervals of a few

minutes, care being taken that the temperature of the solution remains between

�20 and �10 �C. After the addition the temperature is allowed rising to �5 �C

and kept at this level for an additional 15 min. A solution of 0.10 mol of

t-BuOK in 100 ml of DMSO is then added and the mixture is brought at

25 �C. The temperature is allowed rising, but is kept between 35 and 40 �C

by occasional cooling. Stirring is stopped when, after subsiding of the

weakly exothermic reaction, the temperature has dropped again to below

32 �C. A solution of 30 g of ammonium chloride in 300 ml of water is

added, after which the organic layer is washed five times with 50-ml portions

of ammonium chloride solution of the same concentration. The combined

washings are extracted once with 50 ml of pentane and this extract is washed

three times with water. The combined organic solutions are dried over potas-

sium carbonate, after which 1-ethoxyethoxyallene, bp 40 �C/15 Torr (receiver

cooled in a bath at 0 �C), is isolated in an excellent overall yield.

17.2.11 Isomerisation of 1,4-bis(alkoxy)-2-butynesto the corresponding allenes

Scale: 0.20 molar; Apparatus: Figure 1.1, 500 ml, no dropping funnel, no

inert gas

17.2.11.1 Procedure

In 150 ml of anhydrous liquid ammonia (water content<0.1%) 8 g of t-BuOK

is dissolved. 1,4-Dimethoxy-2-butyne (Chapter 20, exp. 20.6.2) (0.20 mol) is

poured into the solution. The reaction mixture is stirred for 25 min after which

20 g of powdered ammonium chloride is introduced over 5 min. The ammonia

is removed by placing the flask in a water bath at 40 �C. Water (200 ml) is then

added and five extractions with 40-ml portions of pentane are carried out. The

combined solutions are freed from t-BuOH by shaking four times with 100-ml

portions of water. The washings are combined and subsequently extracted

twice with small amounts of pentane. The extracts are shaken two times with

water. After drying the solution over potassium carbonate, the greater part of

the pentane is distilled off on a water bath at 70 �C at normal pressure through

an efficient column. The remaining liquid is carefully fractionated to afford

1,4-dimethoxy-1,2-butadiene, bp 38 �C/15 Torr, in �85% yield.


[13.1.2004–9:55pm] [319–340] [Page No. 332]


The isomerisation of 1,4-diethoxy-2-butyne proceeds more slowly. A mixture

of 0.20 mol of t-BuOK, 0.20 mol of the bis-ether and 250 ml of liquid

ammonia is stirred for 2 h, then solid ammonium chloride (20 g) is added

portionwise and the ammonia is removed by evaporation. 1,4-Diethoxy-1,2-

butadiene, bp 59 �C/15 Torr, is obtained in an excellent yield.

4-Ethoxy-1-methoxy-2-pentyne, EtOCH(Me)C�CCH2OMe (obtained by

reaction of 3-methoxy-1-propyne, HC�CCH2OMe, with BuLi followed by

addition of 1-chloro-1-ethoxyethane, MeCH(Cl)OEt), can be converted into

4-ethoxy-1-methoxy-1,2-pentadiene, EtOCH(Me)CH¼C¼CHOMe, by stirring

a mixture of 0.10 mol of t-BuOK, 0.10 mol of the bis-ether and 300 ml of liquid

ammonia for 4 h. The allenic ether, bp 52 �C/15 Torr, is obtained in an excel-

lent yield.

Conversion of 1,1,4-triethoxy-2-butyne, EtOCH2C�CCH(OEt)2, into

1,4,4-triethoxy-1,2-butadiene, EtOCH¼C¼CHCH(OEt)2, with �80% yield is

achieved by adding 1.5 g of powdered t-BuOK in 5 portions with 3-min-inter-

vals to a solution of 0.10 mol of the substrate in 40 ml of DMSO. After 15 min

at 30–35 �C the product, bp 92 �C/15 Torr, is isolated via an aqueous work-up.

17.2.12 1,2,4-Pentatriene from 1-penten-4-yne

Scale: 0.30 molar; Apparatus: 250 ml one-necked flask and thermometer

17.2.12.1 Procedure [9]

Sodium hydroxide (8.0 g) is dissolved in 100 ml of 96% ethanol (Note 1) and

0.30 mol of freshly distilled 1-penten-4-yne (Chapter 19, exp. 19.1.7) is added at

35 �C. After swirling, the refractive index (Note 2) of the solution is measured

(nD �1.387). The solution is kept at 35 �C for 45 min, by which time the

refractive index (nD) had reached its maximal value (�1.396) (Note 3). The

flask is equipped for a distillation and the product is distilled off, together with

a small amount of alcohol and water, and collected in a receiver, cooled below

0 �C (Figure 1.10). The distillation, which takes �15 min (Note 3), is stopped

when the temperature in the head of the column has reached 78 �C. The dis-

tillate is transferred into a small separating funnel and shaken three times with

20-ml portions of a cold (–10 to 5 �C) concentrated ammonium chloride

solution. The upper layer is dried over a small amount of magnesium sulphate.

The refractive index (nD) is 1.470, corresponding to pure 1,2,4-pentatriene.


[13.1.2004–9:55pm] [319–340] [Page No. 333]


The yield is 85–90%. The compound can be stored for a limited period (a few

weeks) at –25 �C.

Notes

1. With NaOH in methanol the isomerisation is markedly slower.

2. A small amount (0.1–0.2 ml) of the solution is sucked into a Pasteur pipette

and the refractive index is measured immediately. The liquid should be

transferred between the prisms in such a way that there is no opportunity

for evaporation as this would result in measuring of a too low value.

3. The ultimate result is a mixture of 1,2,4-pentatriene, H2C¼C¼

CHCH¼CH2, and 3-penten-1-yne, HC�CCH¼CHMe (�9:1). Since the

refractive index of these compounds is between those of vinylallene and

allylacetylene, longer reaction times will result in a decrease of the nD.

Although, the further conversion of vinylallene under the described reac-

tion conditions is much slower, it is safer to keep the reaction time and the

time used for the distillation as short as possible.

17.2.13 1,2-Pentadien-4-yne from 1,4-pentadiene

Scale: 0.10 molar; Apparatus: 100-ml round-bottomed flask and thermo-

meter

17.2.13.1 Procedure [1]

Lithium (0.10 mol) is dissolved in 100 ml of methanol and 0.11 mol of pure

phenol is added (Note 1). From the obtained solution of lithium phenolate,

15 ml is mixed at rt with 0.10 mol of freshly distilled 1,4-pentadiyne (Chapter 4,

exp. 4.5.31). The refractive index (nD) determined immediately after mixing is

1.381 (Note 2). The mixture is then rapidly warmed to 48 �C and kept at this

temperature for 15 min. The nD is now 1.391 (Note 3). Water (100 ml) is then

added and three extractions with 20-ml portions of high-boiling petroleum

ether (bp>180 �C) are carried out. The organic solution is washed with 1 N

hydrochloric acid and subsequently dried over magnesium sulphate. The

extract is warmed in a distillation apparatus, using a water aspirator vacuum


[13.1.2004–9:55pm] [319–340] [Page No. 334]


of 10–15 Torr. The vapour of the yneallene is collected in a receiver cooled at

�75 �C (Figure 1.10). As soon as the petroleum ether begins to pass over,

nitrogen is admitted to the apparatus. This evacuation procedure is repeated

once with the contents of the receiver, now with only slight external heating, so

that the petroleum ether does not boil. In the receiver is collected 3.5 g of

product, consisting of a 9:1 mixture of 1,2-pentadien-4-yne and 1,3-pentadiyne.

This is the best result obtained from several experiments, using various solvents

and bases.

Sodium phenolate gave considerably more 1,3-pentadiyne, and with lithium

p-nitrophenolate as a base the isomerisation to 1,2-pentadien-4-yne was

too slow.

Notes

1. A slight excess of phenol is used. With a stoichiometric amount the solu-

tion may be too strongly basic so that the further isomerisation will

become too fast.

2. A very exact determination is not possible because of the dark brown

colour of the solution.

3. Heating for longer periods gives more 1,3-pentadiyne.

17.2.14 Isomerisation of 3-ethylthio-1-propyne to1-ethylthio-1-propyne

Scale: 0.20 molar; Apparatus: Figure 1.1, 1 litre

Base-catalysed isomerisation of 2-propynyl sulphides, HC�CCH2SR, has

been carried out in ethanol at slightly elevated temperatures. The intermediary

allenic sulphides, H2C¼C¼CHSR, were found to isomerise relatively slowly

to 1-propynyl sulphides, MeC�CSR, under the influence of sodium ethoxide

[5]. We observed an extremely fast isomerisation of propargylic sulphides to

1-propynyl sulphides in boiling liquid ammonia (�33 �C) using sodium ethox-

ide as a catalyst [4]. This base can be prepared by adding an equivalent amount

of ethanol to a solution of sodium or a suspension of sodamide in liquid


[13.1.2004–9:55pm] [319–340] [Page No. 335]


ammonia. Sodium ethoxide prepared in this way is not solvated by ethanol,

which explains its high reactivity. Alternatively, a catalytic amount of t-

BuOK (commercially available) may be added to a mixture of a propargyl

sulphide and liquid ammonia. The propargyl sulphides can be conveniently

prepared in situ by adding propargyl chloride to an ammoniacal solution

of sodium alkanethiolate, formed by adding the thiol to a solution of

sodium in liquid ammonia. Thiols often contain small amounts of disulphides

formed by oxidation. For the preparation of thiolates from thiols and sodium

in ammonia it is not necessary to remove the disulphide by distillation

(complaints about the stench!), as also the disulphide is converted by the

alkali metal into thiolate. Methanethiol is very volatile (bp �6 �C) and it is

experimentally not very attractive to prepare a solution of sodium metha-

nethiolate in liquid ammonia from the thiol. This solution is conveniently

obtained, however, by adding the commercially available dimethyl disulphide,

MeSSMe, to the double equivalent amount of sodium in liquid ammonia

(MeSSMe þ 2 Na ! 2 MeSNa).

17.2.14.1 Procedure

Anhydrous liquid ammonia (300 ml) is placed in the flask and 0.25 mol of

sodium is added in pieces of �0.5 g. After 10 min ethanethiol is added dropwise

over 20 min, while cooling the reaction mixture between �35 and �40 �C. After

the blue colour has vanished, 0.20 mol of propargyl chloride is added over

15 min, likewise with cooling below the bp of ammonia. Salt separates imme-

diately from the solution. After an additional 25 min, a solution of 5 g of t-

BuOK in 50 ml of liquid ammonia (prepared by adding the base to ammonia in

a small round-bottomed or conical flask) is cautiously poured into the reaction

flask (Note). The mixture is vigorously stirred for 5 min, after which the

ammonia is allowed to evaporate overnight (Figure 1.7). Water (�200 ml) is

added with vigorous stirring. After dissolution of the salt, four extractions with

small portions of pentane are carried out. The combined organic solutions are

washed three times with water and subsequently dried over MgSO4. The great-

er part of the pentane is distilled off at atmospheric pressure (40-cm Vigreux

column, bath temperature not higher than 90 �C). Distillation of the remaining

liquid, using a single receiver cooled in a water bath at 0 �C (Figure 1.10)

gives 1-ethylthio-1-propyne, bp �30 �C/15 Torr, in �80% yield.

1-Methylthio-1-propyne, MeC�CSMe, bp �70 �C/100 Torr, is obtained in

slightly lower yield (between 70 and 75%) from MeSNa and HC�CCH2Cl.

The required solution of 0.20 mol of MeSNa is obtained by adding �0.10

mol of dimethyldisulphide, MeSSMe, to a solution of 0.20 mol of sodium in

�300 ml of liquid ammonia, cooled to between –35 and –40 �C.


[13.1.2004–9:55pm] [319–340] [Page No. 336]


Note

If no t-BuOK is available, a solution of 0.10 mol of sodium ethoxide in �100 ml

of liquid ammonia may be added. This solution is obtained in a 1-litre round-

bottomed flask by cautious addition of 0.10–0.13 mol of absolute ethanol to

a solution of 0.10 mol of sodium or to a suspension of 0.10 mol of sodamide

in �150 ml of ammonia.

17.2.15 Isomerisation of 1-(phenylthio)-3-propyne to1-(phenylthio)-1-propyne

Scale: 0.30 molar; Apparatus: 1-litre round-bottomed, three-necked flask,

provided with a dropping tunnel, a mechanical stirrer and a reflux condenser

17.2.15.1 Procedure [5]

A solution of 0.30 mol of sodium ethoxide is prepared by dissolving 0.30 mol of

sodium in 300 ml of 100% ethanol. Thiophenol and propargyl chloride (0.30

mol) are successively added over 15 min without external cooling. Five minutes

later a solution of sodium ethoxide in 100 ml of 100% ethanol, prepared from

3 g of sodium, is run in. The suspension is heated under reflux for an additional

1 h. The reaction mixture is cooled to rt and subsequently poured into 500 ml

of ice water. The product is isolated by extracting five times with Et2O, wash-

ing the extract with water, drying over magnesium sulphate and concentrating

the extract in a water-aspirator vacuum. Distillation through a short column

gives 1-(phenylthio)-1-propyne, bp 100 �C/1 Torr, in an excellent yield.

17.2.16 1,1-Diethoxy-3-heptyne from 1,1-diethoxy-2-heptyne

Scale: 0.10 molar; Apparatus: 250-ml round-bottomed flask and thermometer,

manual swirling


[13.1.2004–9:55pm] [319–340] [Page No. 337]


17.2.16.1 Procedure (cf. [13])

A solution of 1 g of t-BuOK in 8 ml of DMSO is added at rt to a mixture

of 0.10 mol of 1,1-diethoxy-2-heptyne and 30 ml of DMSO. The temperature

rises by a few degrees only. After 10 min a second portion of the solution of

t-BuOK in DMSO is added. After warming the solution for 15 min at 40 �C,

150 ml of ice water is added, followed by extraction with Et2O. The extracts

are dried over magnesium sulphate after washing with water. Careful distilla-

tion of the residue remaining after removal of the solvent under reduced

pressure gives the isomeric acetal, 1,1-diethoxy-3-heptyne, bp 91 �C/10 Torr,

in �70% yield. The small first fraction consists mainly of 1-ethoxy-1-hepten-

3-yne, n-PrC�CCH¼CHOEt.

17.2.17 3-Vinylidene-1-cyclohexene from 1-ethynylcyclohexene

Scale: 0.10 molar; Apparatus: Figure 1.1, 250 ml, without dropping funnel

17.2.17.1 Procedure (cf. [10])

In the flask are placed 40 ml of dry HMPT and 3 g of finely powdered

t-BuOK. The mixture is warmed until all suspended material has dissolved,

then 7.5 g of t-BuOH and 0.10 mol of 1-ethynylcyclohexene are successively

added. Immediately after these additions, the temperature is adjusted at 55 �C.

After stirring for 10 min at 54–56 �C (Note) the brown mixture is poured into

200 ml of ice water and 5 extractions with pentane are carried out. The extracts

are washed with water, dried over magnesium sulphate and then concentrated

under reduced pressure. The isomerisation product, 3-ethenylidene-1-cyclohex-

ene, is collected between 35 and 40 �C/17 Torr in �80% yield. The contamina-

tion of ethylbenzene may vary between 5 and 20% (Note).

Note

Heating for longer periods or at higher temperature gives more ethyl-

benzene.


[13.1.2004–9:55pm] [319–340] [Page No. 338]


17.2.18 Sodamide-catalysed isomerisation of 2-alkynyl ethersto allenic ethers

Scale: 0.20 molar; Apparatus: Figure 1.1, 500 ml, no dropping funnel is used

17.2.18.1 Procedure [11]

The 2-alkynyl ether (0.20 mol) is added in a few seconds to a suspension of

0.40 mol (excess) of sodamide in 250 ml of liquid ammonia. After 15 min the

thermometer is replaced with a powder funnel and 30 g of powdered NH4Cl is

added as quickly as possible. The ammonia is removed by placing the flask in a

bath at 40 �C. Water is added and extraction with Et2O or pentane is carried

out. The extracts are dried and concentrated under reduced pressure. Careful

distillation of the remaining liquid gives 1-ethoxy-4,4-dimethyl-1,2-pentadiene,

bp 46 �C/15 Torr, in >80% yield. The ethers RC�CCH2OEt, R¼ i-Pr,

c-Pentyl and c-Hexyl, can be converted into the corresponding allenic ethers

with high yields, but purities are between 80 and 90% only.

With potassium amide the predominating reaction is 1,4-elimination of etha-

nol with formation of R12C¼CHC�CH through the intermediary cumulenes,

R12C¼C¼C¼CH2 (R

12C ¼ Me2C, (CH2)4C, (CH2)5C, cf. [12]). This elimination

is not possible with the t-butyl derivative.

17.2.19 4,5-Hexadien-3-one from 5-hexyn-2-one

Scale: 0.20 molar; Apparatus: 100-ml round-bottomed flask closed with a

rubber stopper

17.2.19.1 Procedure

A mixture of 0.20 mol of the crude 5-hexyn-3-one (purity �80%, Chapter 20,

exp. 20.4.3), 5 g of sodium hydrogen carbonate and 10 ml of water is shaken

vigorously at rt on a vibrator (or agitated vigorously with a mechanical stirrer).

The isomerisation is followed by determining the refractive index of the upper

layer (shaking or stirring is interrupted for a few minutes). When this has


[13.1.2004–9:55pm] [319–340] [Page No. 339]


reached its maximum value (�1.464) (Note) shaking or stirring is stopped and

the mixture is extracted five times with small portions of diethyl ether. The

extracts are dried (without washing) over magnesium sulphate and, after

removing the solvents in a water-aspirator vacuum, 4,5-hexadien-3-one is

distilled, bp 35–40 �C/15 Torr, yield �85%. The product may contain �15%

of an unknown impurity.

Note

The reaction time at rt is 2–3 h. At 40 �C the isomerisation is finished within

30 min. With a dilute (1 g per 10 ml) aqueous solution of K2CO3 only �5 min

is required.

17.2.20 2,4,5-Hexatrienenitrile from 5-bromo-3-penten-1-yneand potassium cyanide

Scale: 0.10 molar; Apparatus: 250-ml f1ask. Figure 1.1, no dropping funnel

is used

17.2.20.1 Procedure

In the flask is placed 2.0 g of copper(I) cyanide, 15 ml of water, 25 ml of

ethanol and 0.10 mol of 5-bromo-3-penten-1-yne (see below). The mixture is

heated to 60 �C and a solution of 0.11 mol of potassium cyanide in 40 ml of

water is added over 20 min, while keeping the temperature between 60 and

65 �C (occasional cooling may be necessary). After the addition the mixture is

heated for an additional 10 min at 80 �C, then cooled to rt and 200 ml of water

is added. The reaction product is extracted seven times with Et2O. The com-

bined extracts are washed once with a concentrated NH4Cl solution and dried

over magnesium sulphate. Removal of the Et2O by evaporation in a water-

aspirator vacuum gives �9 g of a residue, consisting of equal amounts of

3-hexen-5-ynenitrile and 2,4,5-hexatrienenitrile. This mixture is dissolved in


[13.1.2004–9:55pm] [319–340] [Page No. 340]


25 ml of Et2O and 2 g of potassium carbonate is added. The temperature rises

in a few minutes from 20 to �30 �C. The mixture is shaken for an additional

15 min (by hand or mechanically) and is subsequently poured with swirling

into 50 ml of 2 N hydrochloric acid saturated with ammonium chloride.

After separation of the layers, two extractions with Et2O are carried out.

The combined ethereal solutions are washed once with 50 ml of concentrated

NH4Cl solution and dried over magnesium sulphate. Removal of the solvent

and subsequent distillation through a 30-cm Vigreux column affords the pure

2,4,5-hexatrienenitrile (equal amounts of (E)- and (Z)-isomers), bp 55 �C/15

Torr, in a high yield.

Note

Prepared by addition of the required amount of PBr3 at –10�C to an ethereal

solution of 2-penten-4-yn-1-ol, HC¼CCH¼CHCH2OH (Chapter 4, exp.

4.5.14), to which 5 ml of pyridine has been added. After standing for 2 h at

rt, the mixture is poured into water. 5-Bromo-3-penten-1-yne, bp 40 �C/

15 Torr, is obtained in �75% yield.

REFERENCES

1. Unpublished observations and results from the author’s laboratory.

2. H. D. Verkruijsse, H. J. T. Bos, L. J. de Noten and L. Brandsma, Recl. Trav. Chim., Pays-Bas

100, 244 (1981).

3. S. Hoff, L. Brandsma and J. F. Arens, Recl. Trav. Chim., Pays-Bas 87, 916 (1968).

4. L. Brandsma, H. E. Wijers and J. F. Arens, Recl. Trav. Chim., Pays-Bas 82, 1040 (1963).

5. G. Pourcelot and P. Cadiot, Bull. Soc. Chim. France, 3016 (1966).

6. O. A. Tarasova, F. Taherirastgar, H. D. Verkruijsse, A. G. Mal’kina, L. Brandsma and B. A.

Trofimov, Recl. Trav. Chim., Pays-Bas 115, 145 (1996).

7. W. G. Galesloot, M. J. A. de Bie, L. Brandsma and J. F. Arens, Recl. Trav. Chim., Pays-Bas

89, 575 (1970).

8. G. A. Wildschut, J. H. van Boom, L. Brandsma and J. F. Arens, Recl. Trav. Chim., Pays-Bas

87, 1447 (1968).

9. J. Grimaldi and M. Bertrand, Bull. Soc. Chim. France, 947 (1971).

10. J. P. C. M. van Dongen, A. J. de Jong, H. A. Selling, P. P. Montijn, J. H. van Boom and

L. Brandsma, Recl. Trav. Chim., Pays-Bas 86, 107 (1967).

11. J. H. van Boom, P. P. Montijn, L. Brandsma and J. F. Arens, Recl. Trav. Chim., Pays Bas 84,

31 (1965).

12. P. P. Montijn, H. M. Schmidt, J. H. van Boom, H. J. T. Bos, L. Brandsma and J. F. Arens,

Recl. Trav. Chim., Pays Bas 84, 271 (1965).

13. R. Mantione, M. L. Martin, J. Martin and H. Normant, Bull. Soc. Chim. France, 2912 (1967).


synthesis of acetylenes, allenes and cumulenes || base-catalysed isomerisations of acetylenic...

Documents