synthesis of acetylenes, allenes and cumulenes || allenic compounds by 2,3- and 3,3-sigmatropic...

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E:/Archive files/4188-Brandsma/Printer-Files/4188-Chapter-18.3d

18Allenic Compounds by 2,3- and

3,3-Sigmatropic Rearrangements

18.1 2,3-SIGMATROPIC REARRANGEMENTS

An excellent method for the preparation of allenyl sulphoxides consists of

reacting a propargylic alcohol with a sulphenyl chloride in the presence of

triethylamine. The initially formed product undergoes a 2,3-sigmatropic rear-

rangement at low temperatures to afford the allenic sulphoxide. The formation

of the strong S–O bond is the driving force. Yields are generally high [1–6]

(Scheme 1).

Analogous reactions between propargylic alcohols and sulphinyl chlorides

[7–9] or trivalent phosphorus chlorides [10–19], exemplified by Schemes 2 and

3, respectively, are known.

341

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18.2 3,3-SIGMATROPIC REARRANGEMENTS

Schemes 4–10 represent approaches to the acetylenic starting systems and their

subsequent thermal rearragements [20–31].

There are several other examples of 3,3-sigmatropic rearrangements afford-

ing an allenic system [32–39]. This can be isolated as a relatively stable com-

pound, but in many cases one is concerned with a short-living molecule, which

polymerises or cyclises, unless it is trapped with a reactive reagent. Rearrange-

ments of allenic compounds to acetylenic isomers are less investigated [40].

342 18. 2,3- AND 3,3-SIGMATROPIC REARRANGEMENTS

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18.3 EXPERIMENTAL SECTION

18.3.1 Methyl 1,2-propadienyl sulphoxide from propargylalcohol and methanesulphenyl chloride

Reaction Scheme 1, R1¼H, R2¼Me

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

18.3.1.1 Procedure

To a mixture of 200 ml of dry dichloromethane, 0.22 mol of dry propargyl

alcohol and 0.22 mol of dry triethylamine a solution of 0.20 mol of methane–

sulphenyl chloride (Note 1) in 60 ml of dichloromethane is added with occa-

sional cooling between –95 and –100 �C. After the addition, which takes

� 10 min, 10 g of methyl iodide (Note 2) is added and the cooling bath is

18.3 EXPERIMENTAL SECTION 343

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removed. When the temperature has reached –20 �C, the salt is filtered off on a

sintered-glass funnel (G-2) and rinsed well with dichloromethane. To the resi-

due remaining after evaporation of the solvent in a water-aspirator vacuum is

added 100 ml of dry Et2O in order to precipitate some remaining salt.

Filtration and subsequent removal of the Et2O under reduced pressure gives

pure methyl 1,2-propadienyl sulphoxide in � 100% yield as an oily liquid.

Notes

1. Prepared by adding 0.10 mol of dimethyl disulphide, MeSSMe, at –30 �C

to a solution of 0.10 mol of chlorine in dichloromethane and subsequently

raising the temperature to 0 �C.

2. Traces of unconverted triethylamine might cause partial isomerisation of

the allenyl sulphoxide to the propargyl sulphoxide. The methyl iodide is

added to ensure that no triethylamine remains.

18.3.2 Phenyl 1,2-propadienyl sulphoxide from benzenesulphenylchloride and propargyl alcohol

Reaction Scheme 1, R1¼H, R2¼Ph

Scale: 0.20 molar; Apparatus: Figure 1.1, 500 ml

18.3.2.1 Procedure

In the flask are placed 0.22 mol of the propargyl alcohol, 0.22 mol of triethyl-

amine and 200 ml of dichloromethane (Note 1). To this mixture a solution of

0.20 mol of benzenesulphenyl chloride in 75 ml of dichloromethane (Note 2) is

added in 10 min with occasional cooling between –90 and –100 �C. Five min-

utes after this addition 10 g of methyl iodide is added (Note 3) and the cooling

bath is removed. When the temperature has reached 10–15 �C, the mixture

is poured into 200 ml of water to which 2 ml of 36% HCl has been added.

After vigorous shaking, the lower layer is separated. The aqueous layer is

extracted with 50 ml of dichloromethane. The combined organic solutions

are washed with water and dried over magnesium sulphate. The oily residue

remaining after evaporation of the solvent under reduced pressure appears to

be reasonably pure phenyl 1,2-propadienyl sulphoxide. The yield is almost

quantitative. Small amounts of diphenyl disulphide, which are sometimes pre-

sent, can be removed by shaking the oil with 50 ml of pentane. The disulphide

is extracted in this way. The n20D of phenyl 1,2-propadienyl sulphoxide,

PhS(¼O)CH¼C¼CH2, obtained after this purification is 1.6180.


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1,2-Butadienyl phenyl sulphoxide, PhS(¼O)CH¼C¼CHMe, n20D 1.5993, is

obtained by a similar procedure from 3-butyn-2-ol, HC�CCH(Me)OH, and

benzenesulphenyl chloride, PhSCl.

Notes

1. All reagents and solvents must be thoroughly dry.

2. Prepared by adding at –20 �C a cold (–30 �C) solution of 7.2 g (0.10 mol) of

chlorine in 20 ml of CCl4 to 0.10 mol of diphenyl disulphide in CH2Cl2.

After the addition, which is carried out in 15 min, the temperature is

allowed to rise to 0 �C.

3. See exp. 18.3.1, Note 2.

18.3.3 Methyl 3-methyl-1,2-butadienyl sulphone from2-methyl-3-butyn-2-ol and methanesulphinyl chloride

Reaction Scheme 2, R ¼ Me

Scale: 0.10 molar; Apparatus: Figure 1.1, 500 ml for the preparation of the

sulphinate; 250-ml two-necked flask with a thermometer and a reflux conden-

ser for the rearrangement.

18.3.3.1 Procedure

To a mixture of 0.10 mol of dry 2-methyl-3-butyn-2-ol (commercially avail-

able), 0.12 mol of dry triethylamine and 150 ml of dry dichloromethane

0.12 mol of methanesulphinyl chloride is added over 10 min with cooling at

–50 �C. The cooling bath is removed and after 15 min a mixture of 3 ml of 36%

HCl and 200 ml of water is added with vigorous stirring. The lower layer is

separated, washed with water and dried over magnesium sulphate. The residue

remaining after evaporation of the solvent under reduced pressure is dissolved

in 80 ml of xylene. The solution is heated under reflux for 15 min, then the

xylene is distilled off at 10–20 Torr. The residue is warmed for a few minutes

with 75 ml of dry Et2O. After cooling to 20 �C, the brown solution is decanted

from the small amount of insoluble material. Evaporation of the Et2O

under reduced pressure gives reasonably pure methyl 3-methyl-1,2-butadienyl

sulphone as a brown oil, in a yield of � 85%.

2-Propynyl methanesulphinate, HC�CCH2OSOMe, did not rearrange upon

heating at 130–140 �C in xylene.


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18.3.4 1,2-Propadienyl diphenylphosphinate from propargylalcohol and chlorodiphenylphosphane

Reaction Scheme 3, R ¼ Ph

Scale: 0.10 molar; Apparatus: 500-ml, three-necked, round-bottomed flask

with thermometer, mechanical stirrer and outlet; addition by syringe.

18.3.4.1 Procedure

To a mixture of 100 ml of dry dichloromethane, 0.10 mol of propargyl alcohol

and 0.11 mol of triethylamine is added in 3 min, a solution of 0.10 mol of

diphenylphosphinous chloride, Ph2PCl, in 75 ml of dichloromethane with

cooling between –80 and –90 �C. The cooling bath is removed. When the tem-

perature has reached rt, the reaction mixture is poured into a solution of 2.5 ml

of 36% HCl in 100 ml of water. After vigorous shaking and separation of the

layers, the aqueous layer is extracted twice with 25-ml portions of dichloro-

methane. The combined solutions are washed twice with water, dried

over magnesium sulphate and then concentrated under reduced pressure

giving almost pure 1,2-propadienyl diphenylphosphinate as a white solid,

mp 98–100 �C, in almost 100% yield.

18.3.5 N,N-Diethyl-2-methyl-3,4-pentadienamide from the borontrifluoride-catalysed reaction of propargyl alcohol withN,N-diethyl-1-propyn-1-amine

Reaction Scheme 4

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

condenser.

18.3.5.1 Procedure

To a mixture of 65 ml of dry benzene and 0.10 mol of freshly distilled N,N-

diethyl-1-propyn-1-amine are added 3 drops of BF3-etherate and 0.12 mol of

dry propargyl alcohol is added to the reddish solution in 5 min. The tempera-

ture rises in 5–10 min to � 45 �C, remained at this level for �10 min and

then begins to drop. The mixture is warmed to 60 �C. The temperature rises

in a few minutes to � 85 �C. This level is maintained by occasional cooling.

After the exothermic reaction (3,3-sigmatropic rearrangement) has subsided,

the mixture is heated for an additional 10 minute at 80 �C, then the benzene

is removed under reduced pressure. The red residue is practically pure

carboxamide (NMR). Distillation through a 10-cm Vigreux column gives


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pure N,N-diethyl-2-methyl-3,4-pentadienamide, bp � 70 �C/0.5 Torr, in �85%

yield. A small brown residue remains.

18.3.6 6-Methylhepta-4,5-heptadien-2-one from the acid-catalysedreaction of 2-methyl-3-butyn-2-ol with methylisopropenyl ether

Reaction Scheme 5

Scale: 0.50 molar; Apparatus: Figure 1.1, 500 ml; after the addition of

2-methoxy-1-propene the dropping funnel is replaced with a thermometer

and a reflux condenser is placed on the flask.

18.3.6.1 Procedure

In the flask are placed 1.50 mol (large excess) of 2-methoxy-1-propene

(commercially available) and 0.10 mol of (dry) 2-methyl-3-butyn-2-ol (also

commercially available), and in the dropping funnel 0.40 mol of the latter

compound. The mixture is cooled to 0 �C and 100 mg of anhydrous p-tolue-

nesulphonic acid is added with stirring. An exothermic reaction starts imme-

diately and the temperature rises by several degrees. When this reaction has

subsided, the mixture is cooled to � 10 �C and the remaining 0.40 mol of the

acetylenic alcohol is added from the dropping funnel over 15 min, whilst

keeping the temperature between 10 and 20 �C. The apparatus is then modified

as indicated above and the solution is heated under reflux. In order to maintain

refluxing the bath temperature has to be increased gradually. After 2 h the

temperature in the boiling liquid has become constant (� 95 �C). The brown

solution is cooled, then the volatile components (mainly 2,2-dimethoxypro-

pane) are removed on the rotary evaporator. Subsequent distillation of the

remaining liquid through a 30-cm Vigreux column gives 6-methyl-4,5-hepta-

dien-2-one, bp 65 �C/15 Torr, in �75% yield (Note). There is � 8 g of viscous

residue.

Note

This yield is lower than that reported in the literature. In our procedure no low-

boiling petroleum ether is used as co-solvent so that the temperature of the

boiling reaction mixture can become considerably higher. This may give rise to

the formation of polymeric products and tars. Our reaction time is much

shorter than that in the literature. The reaction with 2-propyn-1-ol,

HC�CCH2OH, and 3-butyn-2-ol, HC�CCH(Me)OH, failed.


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18.3.7 Ethyl 3,4-pentadienoate from the acid-catalysed reaction ofpropargyl alcohol with ethyl orthoacetate

Reaction Scheme 7, R ¼ H

Scale: 0.50 molar; Apparatus: 500-ml three-necked flask equipped with a

dropping funnel, a thermometer dipping in the liquid and an efficient

column connected to a condenser and receiver.

18.3.7.1 Procedure

A mixture of 0.50 mol of 1,1,1-triethoxyethane, 3 g of propionic acid and

0.22 mol of propargyl alcohol is gradually heated in an oil bath. When

� 5 ml of ethanol has passed over (between 75 and 85 �C), another amount

of 0.30 mol of propargyl alcohol is added dropwise over a period of 15 min.

When the temperature of the liquid in the reaction flask has reached 150 �C, the

heating bath is removed and the liquid is allowed to cool to 120 �C. The ethanol

in the receiver is placed in the dropping funnel and mixed with 2 g of propionic

acid, after which the flask is heated again. The mixture of ethanol and acid is

added gradually in 20 min. After the greater part of the ethanol has been

distilled off (� 50 g), the internal temperature can rise to 155 �C. This tempera-

ture is maintained for 30 min, The contents of the flask are allowed to cool to

rt. Very careful fractionation gives ethyl 3,4-pentadienoate, bp 54 �C/17 Torr,

in �60% yield.

18.3.8 Ethyl 3,4-pentadienedithioate from the reaction of ethylethanedithioate with lithium amide and propargyl bromide

Reaction Scheme 6

Scale: 0.30 molar; Apparatus: Figure 1.1, 1 litre for the preparation of the

enethiolate; 1-litre round-bottomed, three-necked flask with mechanical stirrer

and two open necks for the reaction of the enethiolate with propargyl bromide.

18.3.8.1 Procedure

Ethyl ethaneditioate (0.31 mol, prepared from MeMgBr, CS2 and ethyl bro-

mide [41]) is added over a few minutes to a suspension of 0.30 mol of lithium

amide in 250 ml of liquid ammonia (Chapter 2, exp. 2.3.1) with cooling at

� –50 �C. After an additional 5 min the resulting solution (��50 �C) of the

enethiolate is cautiously poured over 5 min through one of the open necks of

the other reaction flask, while keeping the temperature between –50 and

–60 �C. This flask contains a solution of 0.40 mol (excess) of propargyl bromide

in 250 ml of liquid ammonia, cooled to –60 �C which has been made just before


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(Note 1) by adding propargyl bromide to the ammonia pre-cooled at –60 �C.

Four minutes after the addition of the enethiolate to the solution of propargyl

bromide 10 g of powdered ammonium chloride is added. After stirring for an

additional 1 h (without cooling) the reaction mixture is poured onto 300 g of

finely crushed ice on the bottom of a large beaker. Extraction with pentane

(at least 5 times) is carried out as quickly as possible. The extracts are kept

below 0 �C and are washed three times with 1 N hydrochloric acid in order to

remove dissolved ammonia (Note 2). After drying over magnesium sulphate,

the combined organic solutions are concentrated under reduced pressure to a

volume of � 50 ml, care being taken that the bath temperature remains below

rt. The remaining pale yellow solution is brought to � 35 �C. The ensuing

exothermic reaction is kept under control by occasional cooling so that the

temperature does not rise above 45 �C. When, after about half an hour, the

reaction has subsided, the flask is heated for 30 min in a bath at 55 �C.

Removal of the pentane under reduced pressure gives an orange liquid,

being almost pure ethyl 3,4-pentadienedithioate. The yield is at least 75%.

Notes

1. Propargyl bromide reacts very fast with boiling liquid ammonia, therefore

the reaction of it with the enethiolate should be carried out without any

delay. For efficient cooling a bath with liquid nitrogen is indispensable.

2. Since ammonia may catalyse cyclisation of the allenic dithioate to a deriv-

ative of 2H-thiopyran, it seems desirable to neutralise it.

18.3.9 Ethyl 3,4-hexadienoate from the acid-catalysed reactionof 3-butyn-2-ol with ethyl orthoacetate

Reaction Scheme 7, R ¼ Me

Scale: 0.45 molar; Apparatus: same as for exp. 18.3.7

18.3.9.1 Procedure

In the flask are placed 100 g of 1,1,1-triethoxyethane and 2 ml of propionic

acid. From the dropping funnel, which contains 0.45 mol of 3-butyn-2-ol

(commercially available), is added 10 g of this acetylenic alcohol. The flask

is heated in an oil bath. The temperature of the boiling liquid, which initially

is 113 �C, rises to � 130 �C in 20 min, while ethanol distils off at 76–80 �C.

The remainder of the acetylenic alcohol is added dropwise over 30 min. After

heating for 40 min � 50 g of ethanol has passed over and the temperature of the


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liquid in the distillation flask has risen to � 150 �C. Heating at this temperature

is continued for an additional 30 min. After cooling to 30 �C, the remaining

liquid is carefully distilled. After the first fraction, consisting mainly of 1,1,1-

triethoxyethane, has passed over, ethyl 3,4-hexadienoate distils at 65 �C/

15 Torr, and is obtained in �70% yield.

18.3.10 Synthesis of 2,2-dimethyl-3,4-pentadienal starting frompropargyl alcohol and 2-methylpropanal

Reaction Scheme 9

Scale: 0.50 molar; Apparatus: Figure 1.1, 500 ml with long gas inlet tube for

the first reaction; 500 ml round-bottomed three-necked flask with thermo-

meter, mechanical stirrer and reflux condenser for the elimination of hydrogen

chloride and the 3,3-sigmatropic rearrangement.

18.3.10.1 Procedure

Gaseous hydrogen chloride is introduced into a mixture of 0.52 mol of

propargyl alcohol and 0.50 mol of freshly distilled 2-methylpropanal while

keeping the temperature of the mixture between –10 and 0 �C. The introduction

of gas is stopped when copious fumes of HCl escape from the outlet. After

standing for 1–2 min at 0 �C, the clear upper layer is decanted from the small

turbid aqueous layer. The latter is extracted (shaking followed by decanting)

four times with 20-ml portions of pentane. The main portion and the extracts

are dried over a small amount of magnesium sulphate. Subsequently, the pen-

tane is removed on the rotary evaporator keeping the bath temperature at

� 25 �C. The residue (weight � 70 g), crude 3-(1-chloro-2-methylpropoxy)-

1-propyne, is mixed with 120 g of N,N-diethylaniline and the mixture is

heated at 100 �C (internal). A weakly exothermic reaction starts during

which the temperature rises gradually. Some cooling (water bath) is applied

in order to keep the temperature between 100 and 105 �C. Twenty minutes after

the exothermic reaction has ceased the mixture is heated. The diethylaniline

salt of HCl, which has deposited on the glass wall, dissolves. The reaction

mixture is heated under reflux for 10 min (temperature of the reaction mixture

165–170 �C but soon dropping to 150–155 �C). The mixture is cooled to 80 �C

and 300 ml of ice water is added. After shaking (until the salt has dissolved)

and separation of the upper layer, the aqueous layer is extracted once with

30 ml of pentane. The extract and the upper layer are combined and washed

five times with water. After drying over magnesium sulphate, the mixture is

distilled in a weak flow of nitrogen through a 30-cm Vigreux column. The

fraction passing over between 110 and 175 �C/760 Torr is redistilled through


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the same column giving 2,2-dimethyl-3,4-pentadienal, bp 132 �C, in 65–75%

yield (towards the end of the distillation and after cooling, a partial vacuum is

applied to minimise the hold-up).

Starting from propionaldehyde 2-methyl-2,4-pentadienal, H2C¼CHCH¼C(Me)CH¼O, is obtained in an impure state and in moderate yield. Its

precursor, 2-methyl-3,4-pentadienal, H2C¼C¼CHCH(Me)CH¼O, is present

in traces only.

18.3.11 Silver perchlorate-catalysed rearrangement of 1,1-dimethyl-2-propynyl acetate to 3-methyl-1,2-butadienyl acetate

Reaction Scheme 10

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

meter

18.3.11.1 Procedure

To a mixture of 0.10 mol of 1,1-dimethyl-2-propynyl acetate (Chapter 20,

exp. 20.5.1) and 20 g of dry dichloromethane is added at rt 0.60 g of silver

perchlorate. The mixture is swirled for 2–3 min. The perchlorate dissolves

completely and the solution becomes turbid. The temperature rises gradually

to � 30 �C and the solution turns brown to black. After standing for 2 h (Note)

the solution is poured into 100 ml of water to which 4 ml of concentrated

ammonia solution has been added. After vigorous shaking, the organic layer

is separated and combined with two dichloromethane extracts. The combined

solutions are dried over magnesium sulphate and subsequently concentrated

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

short Vigreux column gives the almost pure 3-methyl-1,2-butadienyl acetate,

bp 60 �C/20 Torr, in �55% yield. A rather large residue is left behind.

Note

Longer reaction time gives rise to lower yields and more polymer. With

1-ethynylcyclohexyl acetate (1-acetoxy-1-ethynylcyclohexane) � 50% conver-

sion is effected after 2 h. Addition of more AgClO4 results in a vigorous

decomposition.

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synthesis of acetylenes, allenes and cumulenes || allenic compounds by 2,3- and 3,3-sigmatropic...

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