synthesis of acetylenes, allenes and cumulenes || silylation, stannylation and phosphorylation

[13.1.2004–9:58pm] [161–174] [Page No. 161]

E:/Archive files/4188-Brandsma/Printer-Files/4188-Chapter-07.3d

7Silylation, Stannylation and

Phosphorylation

7.1 INTRODUCTION

Silylated acetylenes are useful synthetic intermediates. Numerous examples are

mentioned in the reviews [1,2]. One can subdivide the applications. In the first

group, the silyl function merely serves as a protector, removed in the last step

of the synthesis. An example is the silylation of a diyne [3], RC�CC�CH, to

give RC�CC�CSiMe3, which by partial reduction with Pd/H2 or activated

zinc in ethanol gives (Z)-RCH¼CHC�CSiMe3. Treatment of this enyne with

alkali hydroxide in methanol or silver nitrate and cyanide [4] finally gives (Z)-

RCH¼CHC�CH. A second type of application concerns reactions in which

the silyl group is substituted by another functionality, e.g. RC(¼O) or halogen.

These transformations are often catalysed by Lewis acids [2]. In the third

category, there can be placed conversions in which silyl substituents facilitate

deprotonation of structure systems CHC�CSi, C�CCHSi, SiC¼C¼CH and

SiCH¼C¼C.

Stannylated and phosphorylated acetylenes have, so far, found fewer appli-

cations as synthetic intermediates. One disadvantage of many organotin com-

pounds is their low volatility and poor propensity to crystallise making

purification by column chromatography necessary. This makes them less

attractive for working on a larger scale.

Silylation, stannylation and phosphorylation of lithium and Grignard deri-

vatives can be carried out under mild conditions in diethyl ether as well as in

tetrahydrofuran.

A survey on the silylation and stannylation of mesomeric acetylenic–allenic

anions can be found on pp. 158–161 of the review [5], for applications of sily-

lated allenes in organic synthesis pp. 252–259 of the monograph [6] may be

referred. Like in the case of other functionalisations, silylation and stannyla-

tion of acetylenic-allenic anions can give either the acetylenic or allenic deriva-

tive as the only product, or afford mixtures of the isomers. The product

161

[13.1.2004–9:58pm] [161–174] [Page No. 162]


composition is determined by the counter ion, solvent and substituents in the

anionic species and in the silylation and stannylation reagents [5]. Reaction of

allenylmagnesium bromide, H2C¼C¼CHMgBr, with chloro(tributyl)stannane,

Bu3SnCl, for example, gives a 95:5 mixture of the allenic and acetylenic stan-

nane, whereas with Ph3SnCl the ratio allenic:acetylenic stannane is 10:90 and

with Me3SnCl 70:30 [7].

Reaction of 1,3-dilithiated acetylenes, LiC�CCH(Li)R (R ¼ Alkyl, Phenyl,

SMe) with one equivalent of chloro(trimethyl)silane occurs at the most

strongly basic propargylic site [8].

7.2 EXPERIMENTAL SECTION

Notes

a. In most of the procedures the reaction mixture is kept under inert gas.

b. Pure chloro(trimethyl)silane is obtained by distillation from � 10%

PhNEt2.

c. Chloro(trimethyl)silane is best stored at room temperature in flasks or bot-

tles with regularly greased ground-glass stoppers. The reagent should never

be stored in screw-capped bottles in the refrigerator, not even when recom-

mended by the supplier.

7.2.1 Ethynyl(trimethyl)silane from ethynylmagnesium bromideand chloro(trimethyl)silane in tetrahydrofuran

Scale: 0.40 molar; Apparatus: Figure 1.1, 1 litre

7.2.1.1 Procedure [9] (cf. [10,11])

Chloro(trimethyl)silane (0.40 mol) is added in two portions over two minutes

(Note) to a vigorously stirred suspension (partly solution) of ethynylmagne-

sium bromide prepared starting from 0.60 mol of ethyl bromide (corresponding

to an excess, Chapter 3, exp. 3.9.7). During and for 30 min after this addition,

the temperature of the reaction mixture is kept between 15 and 20 �C, subse-

quently for 30 min at � 35 �C. The heating effect is not strong. High-boiling

petroleum ether (150 ml, bp > 170 �C) is then added and the slurry is poured

into a cold (–5 �C) solution of 75 g of ammonium chloride in 1 litre of water.

After cautious swirling and shaking, the layers are separated. The organic layer

is ‘washed’ 10 to 15 times with 250-ml portions of ice water in order to remove

162 7. SILYLATION, STANNYLATION AND PHOSPHORYLATION

[13.1.2004–9:58pm] [161–174] [Page No. 163]


the THF. After drying over magnesium sulphate, the ethynylsilane is distilled

off at normal pressure (30-cm Vigreux column). The fraction, collected

between � 45 and 110 �C, still contains some THF. This can be removed by

shaking 5 times with cold dilute hydrochloric acid in a small (100-ml) separat-

ing funnel. Redistillation after drying over a small amount of magnesium

sulphate gives ethynyl(trimethyl)silane, bp 55 �C/760 Torr, in 75–80% yield

(on a 1 molar scale).

Ethynyl(tributyl)stannane, bp 92 �C/1 Torr, is prepared in 85% yield by a

similar procedure using the same molar excess of ethynylmagnesium bromide.

Extraction is carried out with pentane. The synthesis from the LiC�CH.

1,2-ethanediamine complex and Bu3SnCl gave 31% yield only [12].

Note

Slow, dropwise addition involves the chance on formation of Me3SiC�CSiMe3by proton-metal exchange between BrMgC�CH and the kinetically very acidic

HC�CSiMe3 and subsequent silylation.

7.2.2 Procedures for the reaction of alkynyllithium andalkynylmagnesium bromides with chloro(trimethyl)silane

Scale: 0.10 molar; Apparatus: Figure 1.1, 500 ml, addition by syringe

7.2.2.1 General procedure for non-volatile silylacetylenes

Chloro(trimethyl)silane (0.12 mol) is added over a few minutes to a solution of

the metallated acetylene cooled at � –20 �C, then the cooling bath is removed

and the temperature is allowed rising to rt. After an additional 30 min the

reaction mixture (fine or thick suspension) is poured into 100 ml of an aqueous

solution containing 25 g of ammonium chloride. After extraction with Et2O or

pentane and drying over magnesium sulphate, the solvents are removed

under reduced pressure and the remaining liquid distilled in vacuo. Yields are

generally excellent.

7.2.2.2 Rather volatile silylacetylenes

(2-Ethoxyethynyl)(trimethyl)silane, EtOC�CSiMe3, bp 37 �C/10 Torr, is

obtained in >70% yield from the lithium compound (this being used in

7.2 EXPERIMENTAL SECTION 163

[13.1.2004–9:58pm] [161–174] [Page No. 164]


10% excess, Note) and Me3SiCl in Et2O (obtained by removing the greater part

of the hexane from the BuLi solution under reduced pressure subsequently

adding Et2O to the remaining very concentrated solution of BuLi). The silyla-

tion product is isolated by distillation of the greater part of the Et2O at normal

pressure (bath temperature <70 �C) followed by distillation of the remaining

liquid in vacuo. A similar procedure is followed for the isolation of 3-buten-1-

ynyl-(trimethyl)silane, H2C¼CHC�CSiMe3, bp 40 �C/25 Torr (receiving flask

cooled at –5 �C, Figure 1.10).

7.2.2.3 Volatile silylacetylenes

Trimethyl(1-propynyl)silane, MeC�CSiMe3, bp 96 �C/760 Torr, is prepared as

follows:

Chloro(trimethyl)silane (0.30 mol) is added in one portion at 0 �C to a sus-

pension of 0.35 mol of propynyllithium in � 300 ml of Et2O (prepared from an

excess of propyne, cf. Chapter 3, exp. 3.9.4, and BuLi�LiBr in Et2O (Chapter 2,

exp. 2.3.6). The thermometer is replaced with a reflux condenser. The mixture

is stirred at rt for 1 h and subsequently for 6 h under reflux. After cooling to

below 5 �C, the suspension is poured into 100 ml of ice water with occasional

swirling. The aqueous layer is extracted once with a small portion of Et2O, then

the organic solution is dried over magnesium sulphate. Careful fractionation

through an efficient column gives the desired silylation product, bp 95 �C/

760 Torr, in >70% yield.

A similar procedure may be applied to prepare EtC�CSiMe3.

Note

1-Alkynyl ethers very easily react with water in the presence of acid to give

esters. The use of an excess of the lithiated acetylenic ether guarantees the

absence of acid during the work-up.

7.2.3 Reaction of lithiated propargyl chloride withchloro(trimethyl)silane

Scale: 0.10 molar; Apparatus: Figure 1.1 , 500 ml, addition by syringe


[13.1.2004–9:58pm] [161–174] [Page No. 165]


7.2.3.1 Procedure

Freshly distilled chloro(trimethyl)silane (0.09 mol, less than the equivalent

amount, Note 1) is added at –90 �C to a solution of 0.10 mol of lithiated

propargyl chloride in a mixture of THF (Note 2) and hexane (Chapter 3,

exp. 3.9.6). Dry DMSO (25 ml) is added over 1–2 min at –90 �C, after which

the cooling bath is removed and the temperature allowed rising to rt. Water

(100 ml) is added, followed by extraction with pentane. The organic solution is

dried over magnesium sulphate. The greater part of the solvents is distilled off

under atmospheric pressure. (3-Chloro-1-propynyl)(trimethyl)silane, bp 45 �/

15 Torr, is obtained in >70% yield.

Notes

1. There should be no risk that any Me3SiCl remains unconverted. This will

form hexamethyldisiloxane, Me3SiOSiMe3, during the aqueous work-up.

Complete separation of this compound and the product is not possible.

2. Et2O presumably also can be used and addition of DMSO is probably

unnecessary when THF is used as the main solvent.

7.2.4 Reaction of lithiated propargyl bromide withchloro(trimethyl)silane


7.2.4.1 Procedure [13]

Chloro(trimethyl)silane (0.30 mol, excess) is added over 5 min to a solution

of 0.20 mol of lithiated propargyl bromide in 200 ml of Et2O and 126 ml

of hexane (Chapter 3, exp. 3.9.6) cooled to between –80 and –90 �C.

Subsequently a mixture of 25 ml of dry HMPT or DMSO and 30 ml of

Et2O is added dropwise over 5 min with efficient stirring while carefully

keeping the temperature within this range. After this addition the cooling

bath is occasionally removed and the temperature is allowed to rise gradually

over 30 min to –40 �C, and subsequently to 10 �C. The white suspension is then

poured into 500 ml of 2 N aqueous HCl and the product is isolated as described

in exp. 7.2.3 (the solvent and volatile components are removed under reduced

pressure). Careful distillation through a 40-cm Vigreux column gives (3-bromo-

1-propynyl)(trimethyl)silane, bp 58 �C/15 Torr, in � 80% yield. Possibly, good


[13.1.2004–9:58pm] [161–174] [Page No. 166]


results can be obtained also when a smaller amount or no co-solvent is used: in

this case the mixture of lithiated propargyl bromide and chloro(trimethyl)si-

lane has to be stirred for at least 2 h at � –80 �C.

7.2.5 Trimethyl[(2-trimethylsilyl)ethynyl]silane fromacetylene-1,2-bis(magnesium bromide) andchloro(trimethyl)silane

Scale: 0.50 molar (Me3SiCl); Apparatus: Figure 1.1, 1 litre

The trimethylsilylation of the di-Grignard derivative of acetylene has to be

carried out at temperatures that are considerably higher than necessary for

the silylation of ethynyl mono-magnesium bromide. This decreased reactivity

may be ascribed to the slight solubility of the intermediate.

7.2.5.1 Procedure

Chloro(trimethyl)silane (0.60 mol) is added dropwise over 20 min to a suspen-

sion of 0.25 mol of acetylene dimagnesium bromide in � 500 ml of THF

(cf. Chapter 3, exp. 3.9.8) kept between 50 and 55 �C by occasional cooling

or heating. The suspension disappears gradually. The mixture is heated to

50–55 �C for an additional period of 2 h, then cooled to � 30 �C and subse-

quently poured into a solution of 25 g of NH4Cl in 200 ml of water. After

vigorous shaking, the aqueous layer is extracted twice with 75-ml portions of

pentane. The combined organic solutions are washed 10 times with 50-ml

portions of an aqueous solution of NH4Cl (150 g/litre) in order to remove as

much of THF as possible. The organic layer is dried over MgSO4. Distillation

of the remaining liquid through a 40-cm Vigreux column gives trimethyl

[2-(trimethylsilyl)ethynyl]silane, Me3SiC�CSiMe3, bp 128–138 �C/ 760 Torr

in greater than 80% yield. The product solidifies slowly at rt.

7.2.6 1,3-Butadiynyl(tributyl)stannane from butadiynyllithiumand chloro(tributyl)stannane

Scale: 0.10 molar (Bu3SnCl); Apparatus: Figure 1.1, 500 ml


[13.1.2004–9:58pm] [161–174] [Page No. 167]


In some derivatisation reactions with mono-metallated butadiyne consider-

able amounts of disubstituted diacetylene are formed. Their presence can

hamper the purification of the desired mono-substitution products, particu-

larly when the boiling point is high and the thermal stability limited. The for-

mation of disubstitution products can be effectively suppressed, however, by

using a large excess of butadiyne. The preparation of butadiynyl tributyltin

is an illustrative example.

7.2.6.1 Procedure

A solution of 0.13 mol of BuLi in 82 ml of hexane is added dropwise over

20 min to a mixture of 0.25 mol of diacetylene (freshly prepared, or stored

as a THF solution at –80 �C, see Chapter 10, exp. 10.2.7) and 100 ml of THF.

During this addition the temperature is kept below –40 �C.

Chloro(tributyl)stannane (0.10 mol) is then added at –30 �C over 2 min, after

which the cooling bath is removed. The mixture is stirred for an additional 2 h

at 0 �C, then it is poured into a solution of 25 g of NH4Cl in 200 ml of water.

After separation of the layers, one extraction with pentane is carried out.

The organic solutions are dried over MgSO4 and subsequently concentrated

in vacuo. The last traces of volatile components are removed in a vacuum of

0.5 Torr or less. The residue is � 100% pure 1,3-butadiynyl(tributyl)stannane,

as indicated by 1H NMR. Distillation is not carried out.

7.2.7 Reaction of allenylmagnesium bromide withchloro(trimethyl)silane and chloro(tributyl)stannane

Scale: 0.10 molar; Apparatus: Figure 1.1, 500 ml

7.2.7.1 Procedure

A solution of allenylmagnesium bromide in � 150 ml of Et2O, prepared from

0.15 mol of propargyl bromide (Chapter 2, exp. 2.3.9) is cooled to –10 �C.

Freshly distilled chloro(trimethyl)silane (0.10 mol) or chloro(tributyl)stannane

(0.10 mol) is added dropwise over 20 min with efficient stirring while main-

taining the temperature at the level mentioned. A thick suspension is formed in


[13.1.2004–9:58pm] [161–174] [Page No. 168]


the case X ¼ Si. After an additional 15 min, as much of the suspension as

possible is poured into a solution of 20 g of ammonium chloride in 100 ml of

water. The suspension remaining in the flask is hydrolysed by cautious addition

of aqueous NH4Cl. After vigorous shaking, the layers are separated. The com-

bined organic layer and one extract, using only a small amount of Et2O, are

dried over MgSO4, after which a very careful distillation through an efficient

column is carried out. Trimethyl(2-propynyl)silane (containing � 8% of tri-

methyl(1,2-propadienyl)silane), bp � 92 �C/760 Torr, is obtained in a fair

yield (>75% in 0.5 molar-scale experiments).

In the case of X ¼ Sn, the reaction mixture is kept at rt during the night,

followed by the work-up described above. Removal of the Et2O under

reduced pressure gives an � 95:5 mixture of tributyl(1,2-propadienyl)stannane

and tributyl(2-propynyl)stannane in quantitative yield.

7.2.8 Trimethylsilylation of lithiated N,N-diethyl-1-allenamine



A solution of 0.12 mol of anhydrous lithium bromide in 40 ml of THF is

added at � – 50 �C to a solution of 0.10 mol of the potassiated N,N-diethyl-

1-propyn-1-amine in THF and hexane prepared as described in Chapter 3,

exp. 3.9.18. Subsequently, Me3SiCl (0.12 mol) is added over 10 min at

–60 �C to the resulting gel-like suspension. The cooling bath is removed and

when the temperature has reached 10 �C, the mixture is poured into 150 ml of

an aqueous solution of 5 g of potassium carbonate. After shaking, extraction

with Et2O (3 times) and drying over potassium carbonate, the solvents are

removed under reduced pressure. Distillation of the crude product gives

N,N-diethyl-3-(trimethylsilyl)-1-propyn-1-amine, bp 75 �C/15 Torr, in greater

than 80% yield.

A similar procedure, carried out without preceding addition of lithium

bromide, gives a 2:1 mixture of the silylated acetylenic amine and N,N-

diethyl-3-(trimethylsilyl)-1-allenamine. The lithium derivative H2C¼C¼

C(Li)NMe2 and Me3SiCl give equal amounts of the acetylenic and the allenic

silane [14].


[13.1.2004–9:58pm] [161–174] [Page No. 169]


7.2.9 Trimethylsilylation of a lithiated 2-alkyne


7.2.9.1 Procedure

Chloro(trimethyl)silane (0.12 mol) is added in one portion to a solution of

lithiated 2-nonyne (Chapter 3, exp. 3.9.16 and Table 3.3) cooled at � –60 �C,

after which the cooling bath is removed. After 10 min water is added, followed

by extraction of the aqueous layer. The organic solution is dried and concen-

trated under reduced pressure. Trimethyl(2-nonynyl)silane, bp 95 �C/15 Torr,

is obtained in an excellent yield.

Lithiated 2-alkynyl ethers, RC�CCH(Li)OR1, can be silylated under similar

conditions to give pure allenic derivatives [15], RC(SiMe3)¼C¼CHOR1.

7.2.10 Trimethylsilylation of a lithiated cumulenic amine


7.2.10.1 Procedure [18]

Chloro(trimethyl)silane (0.05 mol) is added over a few seconds to a solution of

the lithiated N,N,4-trimethyl-1,2,3-pentatrien-1-amine (Chapter 3, exp. 3.9.32)

in THF–hexane cooled at � –80 �C, after which the cooling bath is removed.

When the temperature has reached –30 �C, water (100 ml) is added with vigor-

ous stirring, care being taken to keep the temperature below 5 �C. The organic

layer and two ethereal extracts are dried over potassium carbonate and

concentrated under reduced pressure. Distillation of the crude product

through a very short column gives [N,N,4-trimethyl-1-(trimethylsilyl)-1,2,3-

pentatrien-1-amine, bp 52 �C/0.2 Torr, in �65% yield. The product is extre-

mely oxygen-sensitive.


[13.1.2004–9:58pm] [161–174] [Page No. 170]


7.2.11 Trimethylsilylation of lithiated methoxyallene

Scale: 0.10 molar (Me3SiCl); Apparatus: Figure 1.1, 500 ml, addition by syringe

7.2.11.1 Procedure

Chloro(trimethyl)silane (0.10 mol) is added over a few minutes at –30 �C to a

solution of 0.12 mol of 1-lithio-1-methoxyallene (excess, Note) prepared as

indicated in Chapter 3, exp. 3.9.15 and Table 3.3 from methoxyallene and

BuLi�LiBr in Et2O (Chapter 2, exp. 2.3.6). The cooling bath is removed and

the suspension is allowed to reach rt, then 100 ml of an aqueous solution of 20

g of ammonium chloride is added with vigorous stirring. After extraction with

Et2O, the organic solution is dried over magnesium sulphate and the Et2O is

distilled off under normal pressure (bath temperature <90 �C) through a

40-cm Vigreux column. Distillation of the remaining liquid gives (1-methoxy-

1,2-propadienyl) (trimethyl)silane, bp � 25 �C/15 Torr, (receiver cooled in a

bath at –5 �C, Figure 1.10) in � 70% yield.

Stannylation of lithiomethoxyallene (10% excess) with Bu3SnCl (–30�C!

rt) gives tributyl(1-methoxy-1,2-propadienyl)stannane (not distilled) contami-

nated with � 10% of tributyl(3-methoxy-2-propynyl)stannane, Bu3SnCH2C�

COMe, in almost 100% yield.

Note

Allenic ethers react with water in the presence of acid. The use of an excess

of the lithiated allenic ether ensures the absence of acid during the aqueous

work-up.

7.2.12 3-(Trimethylsilyl)-2-propyn-1-ol



[13.1.2004–9:58pm] [161–174] [Page No. 171]


7.2.12.1 Procedure

Freshly distilled (under � 100 Torr) propargyl alcohol (0.10 mol) is added

over a few minutes to a solution of 0.20 mol of BuLi �LiBr (Chapter 2,

exp. 2.3.6) in � 200 ml of Et2O with cooling between –10 and –30 �C.

Subsequently, 0.22 mol of chloro(trimethyl)silane is added over 15 min at

� –10 �C. The suspension is stirred for an additional 2 h at rt, then a mixture

of 10 g of acetic acid and 70 ml of water is added with vigorous stirring.

Stirring is continued for 4 h at rt. The aqueous layer is extracted four times

with Et2O. The combined organic solutions are shaken with a saturated aqu-

eous solution of NaHCO3 in order to remove the acetic acid. After drying over

magnesium sulphate, the Et2O is removed under reduced pressure. 3-

(Trimethylsilyl)-2-propyn-1-ol, bp 71 �C/15 Torr, is obtained in a high yield.

If the disilyl compound appears to be present, the product should be stirred for

a few minutes with 1 M hydrochloric acid.

The dilithiation of propargyl alcohol can be carried out also with a mixture

of commercial BuLi in hexane and THF.

7.2.13 Regioselective monosilylation of 1,3-dilithiated alkynes



Chloro(trimethyl)silane (0.10 mol) is added dropwise over 30 min to a solution

of the 1,3-dilithiated acetylene in THF and hexane (Chapter 3, exp. 3.9.11) with

cooling at –70 �C, then the cooling bath is removed. After an additional 30 min

ice water is added, followed by extraction. The organic solution is dried over

magnesium sulphate and concentrated under reduced pressure. Trimethyl

(1-phenyl-2-propynyl)silane, HC�CCH(SiMe3)Ph, bp 102 �C/18 Torr,

trimethyl[1-methylthio-2-propynyl]silane, HC�CCH(SiMe3)SMe, bp 65 �C/

18Torr, and (1-butyl-2-propynyl)(trimethyl)silane, HC�CCH(SiMe3)Bu, bp

55 �C/17 Torr, are obtained in >70% yields.

7.2.14 Dibutyl(ethynyl)phosphane


[13.1.2004–9:58pm] [161–174] [Page No. 172]



7.2.14.1 Procedure [16]

(Note 1) Into a solution of � 0.2 mol of ethynylmagnesium bromide in � 200ml

of THF (Chapter 3, exp. 3.9.7) acetylene is introduced (100 ml/min) for 15 min

with cooling at –15 �C. The resulting suspension is cooled to � –25 �C, after

which dibutylphosphinous chloride [17] (0.10 mol) is added over 15 min. After

this addition, the cooling bath is removed and the temperature is allowed rising

to þ10 �C. A solution of 20 g of NH4Cl in 200 ml of water is then added over a

few minutes with vigorous stirring. After separation of the layers and extrac-

tion of the aqueous layer with Et2O, the extracts are dried over MgSO4 (Note 2)

and subsequently concentrated under reduced pressure. Distillation through a

30-cm Vigreux column gives dibutyl(ethynyl)phosphane, bp 85 �C/10 Torr, in

�75% yield (Note 3). Crystallisation of the solid residue from Et2O gives a

small amount of Bu2PC�CPBu2, mp 32–33 �C.

Notes

1. In view of the oxygen-sensitivity of phosphanes all operations must be

carried out in a nitrogen atmosphere.

2. The amount of MgSO4 should be as small as possible. Instead of being

filtered, the organic solution is carefully decanted from the drying agent,

which is rinsed a few times with Et2O.

3. After termination of the distillation nitrogen must be admitted!

7.2.15 Diethynyl(phenyl)phospane

Scale: 0.10 molar (PhPCl2); Apparatus: Figure 1.1, 500 ml

7.2.15.1 Procedure (cf. exp. 7.2.14)

(Note 1) Acetylene (� 300 ml/min) is introduced for 5 min into a suspension of

0.25 mol of ethynylmagnesium bromide in 300 ml of THF (Chapter 3, exp.

3.9.7) cooled to between –20 and –30 �C. Subsequently dichlorophenylpho-

sphane (0.10 mol, commercially available) is added dropwise over 15 min

while keeping the temperature between –10 and –20 �C. After an additional


[13.1.2004–9:58pm] [161–174] [Page No. 173]


30 min the cooling bath is removed and the temperature allowed rising to 0 �C.

The suspension is then treated with a solution of NH4Cl in water as described

in exp. 7.2.14. The work-up is also carried out in a similar way. Distillation of

the remaining brown liquid through a very short and wide column (preferably

B-29 glass joints) in a high vacuum (mercury-diffusion pump, pressure

0.01 Torr or lower) gives the acetylenic phosphine, bp � 50–60 �C/0.01 Torr,

in �50% yield. The temperature of the heating bath should not exceed 80 �C

since the residue may decompose vigorously upon excessive heating.

7.2.16 Tri(1-propynyl)phosphane

Scale: 0.10 molar (PCl3); Apparatus: Figure 1.1, 1 litre

7.2.16.1 Procedure [16]

(Note) A solution of 0.45 mol of propynylmagnesium bromide (Chapter 3,

exp. 3.9.9, note) in 350 ml of THF is added dropwise or portionwise over

30 min to a mixture of 0.10 mol of freshly distilled PCl3 and 100 ml of THF

while keeping temperature between –70 and –90 �C by occasional cooling in a

bath with liquid N2. After the addition, the temperature of the reaction mixture

is allowed to rise gradually over 3–4 h to 0 �C. Stirring at 0 �C is continued for

another 1 h. The brown suspension is then poured into a concentrated aqueous

solution of NH4Cl. After vigorous shaking and separation of the layers, the

aqueous layer is extracted with Et2O. The organic solution is dried over MgSO4

and subsequently concentrated under reduced pressure, giving reasonably pure

(94%) tri(1-propynyl)phosphane. Recrystallisation from Et2O gives the pure

compound in � 80% yield, mp 95–96 �C.

Note

All operations, including the work-up, must be carried out under nitrogen.

REFERENCES

1. D. R. M. Walton, in Protective Groups in Organic Chemistry (ed. J. F. W. McOmie). Plenum

Press, 1973, p. 2.

2. E. W. Colvin, Silicon in Organic Synthesis. Butterworths, 1981.

REFERENCES 173

[13.1.2004–9:58pm] [161–174] [Page No. 174]


3. M. H. P. J. Aerssens, R. van der Heiden, M. Heus and L. Brandsma, Synth. Commun. 20, 3421

(1990).

4. H. M. Schmidt and J. F. Arens, Recl. Trav. Chim., Pays-Bas 86, 1138 (1967).

5. R. Epzstein, review in Comprehensive Carbanion Chemistry, Part B (eds. E. Buncel and

T. Durst). Elsevier, Amsterdam, 1984, p. 99.

6. H. E. Schuster and G. M. Coppola, Allenes in Organic Synthesis. Wiley-Interscience, New

York, 1984, p. 252.

7. M. le Quan and P. Cadiot, Bull. Soc. Chim. France, 45 (1965); J.-C. Masson, M. le Quan and

P. Cadiot, Bull. Soc. Chim. France, 777 (1967).

8. H. Hommes, H. D. Verkruijsse and L. Brandsma, Recl. Trav. Chim. Pays- Bas 99, 113 (1980).

9. L. Brandsma and H. D. Verkruijsse, Synthesis, 1727 (1999).

10. E. R. H. Jones, L. Skattebøl and M. C. Whiting, Org. Synth., Coll. Vol. 4, 792.

11. A. B. Holmes and C. N. Sporikou, Org. Synth., Coll. Vol. 8, 606 (1993).

12. A. F. Renaldo, J. F. Labadie and J. K. Stille, Org. Synth., Coll. Vol. 8, 268 (1993).

13. H. D. Verkruijsse, L. Brandsma, Synth. Commun. 20, 3375 (1990).

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

15. Y. Leroux and C. Roman, Tetrahedron Lett., 2585 (1973).

16. W. Voskuil and J. F. Arens, Recl. Trav. Chim., Pays-Bas 88, 993 (1962); 83, 1301 (1964).

17. K. Issleib and W. Seidel, Chem. Ber. 92, 2681 (1959).

18. P. E. van Rijn and L. Brandsma, J. Organometal. Chem. 233, C25 (1982).


synthesis of acetylenes, allenes and cumulenes || silylation, stannylation and phosphorylation

Documents