synthesis of acetylenes, allenes and cumulenes || cumulenes by dehalogenation of geminal...

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E:/Archive files/4188-Brandsma/Printer-Files/4188-Chapter-11.3d

11Cumulenes by Dehalogenation of

Geminal Dihalogenocyclopropanes

11.1 INTRODUCTION

A wide variety of allenic and cumulenic derivatives, including cyclic ones,

can be synthesised by addition of dihalocarbene to an olefinic compound

and subsequent treatment of the geminal dihalocyclopropane with a

reducing reagent. As such zinc, magnesium, sodium, NaEt3BH, a copper(0)

isonitrile complex, Grignard reagents, chromium(II) chloride and alkyllithium

reagents have been used. The latter are generally employed. For literature the

reader of this book is referred to monographs [1,2] and reviews [3–9].

The generally accepted course of the reaction between geminal dihalocyclo-

propanes and alkyllithium involves a sequence of halogen/lithium exchange,

elimination of lithium halide from the intermediary carbenoid and rupture

of the cyclopropane ring in the transient carbene with formation of two cumu-

lated double bonds.

If suitably positioned functionalities are present in the cyclopropane

derivative, the carbene may undergo an insertion into a C–H bond (e.g.

in the case of –CH2–O–CCH2Me) or add to a double bond (of (C)nCH¼C)

resulting in the formation of exotic bi- and polycyclic structures as by or

main products.

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11.2 EXPERIMENTAL SECTION

11.2.1 Synthesis of [1-(2,3-butadienyl)benzene]

Scale: 0.20 molar (last step); Apparatus: Figure 1.1, 500 ml

11.2.1.1 Procedure for allylbenzene

To a refluxing solution of phenylmagnesium bromide in 650 ml of Et2O,

prepared from 1.15 mol of bromobenzene, is added 1.00 mol of allyl bromide

at a rate such that refluxing is maintained (about 30 min). Thirty minutes after

refluxing has stopped, a trace of copper(I) bromide is added in order to complete

the conversion. The reaction mixture is cautiously poured on to 500 g of finely

crushed ice, then 200 ml of 4 N hydrochloric acid is added. After the remaining

ice has melted, the layers are separated and the aqueous layer is extracted three

times with Et2O. The combined ethereal solutions are washed with saturated

NaCl solution and dried over magnesium sulphate. The greater part of the Et2O

is distilled off at normal pressure through a 40-cm Vigreux column. Distillation

of the residue gives allylbenzene, bp 44 �C/15 Torr, in 90% yield.

11.2.1.2 Procedure for 1-[(2,2-dibromocyclopropyl)methyl]benzene

To a solution of 250 g of NaOH in 275 ml of water is added at rt 0.5 g of

triethylbenzyl ammonium chloride (TEBA), 5 ml of ethanol, 0.50 mol of allyl-

benzene and 1.00 mol of bromoform and the mixture is vigorously stirred. The

temperature rises to about 45 �C in 10–15 min and is kept at that level by

occasional cooling. Stirring is continued for 10 h at rt after the exothermic

reaction has subsided. After addition of 1 litre of ice water, the product is

extracted with Et2O (for the first extraction a sufficient amount has to be

used to obtain an upper layer). The combined ethereal solutions are washed

with water and dried over magnesium sulphate. After the Et2O has been

230 11. CUMULENES BY DEHALOGENATION

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removed by evaporation in a water-aspirator vacuum, the residue is subjected

to a high-vacuum distillation (0.5 Torr), keeping the temperature of the heating

bath below 100 �C. The residue remaining after the unconverted bromoform

has been distilled off (bp <60 �C/0.1–0.5 Torr) weighs 120 g and consists of the

reasonably pure cyclopropane derivative.

11.2.1.3 Procedure for 4-phenyl-1,2-butadiene

Of the crude adduct, 65 g (corresponding to 0.20 mol plus an excess) is

dissolved in 175 ml of dry Et2O. A solution of 0.20 mol of BuLi in 126 ml

of hexane is added dropwise over 30 min, while maintaining the tempera-

ture at � –60 �C. After the addition, the temperature is allowed to rise to

–25 �C and stirring at that level is continued for an additional 30 min. The

mixture is then poured with swirling into 1 litre of ice water. The upper

layer and two extracts of the aqueous layer are combined and dried over

magnesium sulphate. The solvents are removed in a water-aspirator vacuum.

Distillation of the residue gives 4-phenyl-1,2-butadiene, bp 75 �C/15 Torr,

in >80% yield.

11.2.2 Cyclonona-1,2-diene

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

11.2.2.1 Procedure

A mixture of 0.20 mol of 9,9-dibromobicyclo[6.1.0]nonane (procedure similar

to preceding experiment) and 250 ml of dry Et2O is cooled to –65 �C. A

solution of 0.21 mol of BuLi �LiBr in 200 ml of Et2O (Chapter 2, exp. 2.3.6)

or 0.21 mol of (commercial) BuLi in 133 ml of hexane is added over 15 min

with cooling between –60 and –50 �C. After the addition, the cooling bath is

removed, the temperature is allowed to rise to �–10 �C and the reaction

mixture is poured into 200 ml of ice water. The aqueous layer is extracted

twice with Et2O. After drying, the solvent is removed under reduced pressure

and the remaining liquid is distilled through a 40-cm Vigreux column.

1,2-Cyclononadiene, bp 62 �C/22 Torr, is obtained in >80% yield.

11.2 EXPERIMENTAL SECTION 231

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11.2.3 1,2,3-Cyclodecatriene

Scale: 0.05 molar (last step); Apparatus: 250-ml three-necked flask, equipped

with a gas inlet, a thermometer and an outlet; magnetic stirring; addition by

syringe

11.2.3.1 Procedure for 10,10-dichlorobicyclo[7.1.0]-1-decene

To 75 ml of a 50% aqueous solution of KOH are added 0.25 mol of chloro-

form, 0.2 g of triethylbenzyl ammonium chloride (TEBA) and 0.10 mol of

freshly distilled 1,2-cyclononadiene (see preceding exp.). The mixture is stirred

vigorously for 10–12 h at rt. Water (200 ml) is then added and the product is

extracted with Et2O. The extract is dried over magnesium sulphate, concen-

trated under reduced pressure and the residue is distilled through a short

Vigreux column. The dichlorocyclopropane derivative, bp 80 �C/0.15 Torr, is

obtained in �75% yield.

11.2.3.2 Procedure for 1,2,3-cyclodecatriene

A solution of 0.06 mol of BuLi �LiBr (Chapter 2, exp. 2.3.6) in � 50 ml of Et2O

is added in 15 min to a solution of 0.05 mol of 10,10-dichlorobicyclo[7.1.0]-

1-decene in 40 ml of Et2O. After this addition, carried out at � –55 �C, the

temperature is allowed to rise to –25 �C. The colour of the mixture changes

from light yellow to green. After addition of 50 ml of a saturated ammonium

chloride solution (Note) and shaking, the layers are separated and the upper

layer is dried over magnesium sulphate. The aqueous layer is extracted twice

with Et2O or pentane and the combined solutions are concentrated under

reduced pressure. The last traces of solvent are removed in a high vacuum.

During this operation the bath temperature is kept at � 10 �C. The residue

(yield >90%) consists of reasonably pure 1,2,3-cyclodecatriene (1H NMR).

Attempted distillation results in polymerisation.

Note

Cumulenes are extremely air-sensitive. All operations during the work-up must

be carried out under nitrogen.


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11.2.4 Tetramethylbutatriene

Apparatus: Ketene generator (500 ml distillation flask) [10] for the preparation

of tetramethylallene; for the addition of dichlorocarbene a 1-litre round-

bottomed, three-necked flask, provided with a mechanical stirrer, a thermo-

meter and an outlet; for the dechlorination a 500-ml flask (Figure 1.1)

11.2.4.1 Preparation of 2,4-dimethyl-2,3-pentadiene

The ketene generator is connected to two cold traps (–80 �C). Between the traps

and the water aspirator is placed a tube filled with calcium chloride lumps.

In the distillation flask is placed 1.0 mol of the commercially available

3,3-dimethyl-4-(1-methylethylidene)-2-oxetanone. After evacuation of the

apparatus (10–20 Torr) the flask is heated in a bath at 95–105 �C and the

voltage is adjusted (� 50 V) so that complete decomposition of the lactone

vapour occurs (no reflux). After 60–80 min, the electrical heating of the glow-

ing spiral is terminated and the heating bath is removed. After the generator

has cooled, nitrogen is admitted and the contents of the traps are distilled

under normal pressure. 2,4-Dimethyl-2,3-pentadiene, bp 86 �C/760 Torr, is

obtained in �80% yield. The residue in the reaction flask of the ketene appa-

ratus consists mainly of starting compound.

11.2.4.2 Addition of dichlorocarbene to 2,4-dimethyl-2,3-pentadiene

To 250 ml of a 50% aqueous solution of KOH is added 0.45 mol of tetra-

methylallene, 0.90 mol of chloroform and 0.10 g of triethylbenzylammonium

chloride and the mixture is agitated vigorously without external cooling. After

4 h the mixture is cooled to rt and 200 ml of ice water is added. After extraction

with Et2O and drying of the light yellow solution over magnesium sulphate,

the solvent is removed under reduced pressure. Distillation (Note 1) gives

1,2-dichloro-2,2-dimethyl-3-(1-methylethylidene)cyclopropane, bp 59 �C/Torr,

in �80% yield.

11.2 EXPERIMENTAL SECTION 233

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11.2.4.3 Preparation of 2,5-dimethyl-2,3,4-hexatriene

A solution of 0.10 mol of 1,2-dichloro-2,2-dimethyl-3-(1-methylethylidene)-

cyclopropane in 130 ml of dry Et2O is cooled to –35 �C. A solution of 0.12

mol of BuLi in 76 ml of hexane is added dropwise over 30 min, while main-

taining the temperature of the reaction mixture close to –30 �C. After this

addition the cooling bath is removed, the temperature is allowed to rise to

–10 �C and a concentrated aqueous solution (50 ml) of ammonium chloride

is added with vigorous stirring. The upper layer is separated and dried (without

washing) over magnesium sulphate. The volatile components are removed

under reduced pressure, keeping the bath temperature below 20 �C. The residue

is distilled through a short column and collected in a single receiver cooled at

0 �C. Tetramethylbutatriene passes over at 40 �C/18 Torr. It solidifies in the

receiver. The yields vary from 60 to 80% (Note 2).

Notes

1. In view of strong foaming, a 500-ml distillation flask should be used.

2. Traces of oxygen cause polymerisation of the cumulene. All operations

must be carried out under nitrogen.

3. Under pure nitrogen at �80 �C the compound can be kept unchanged for

several days.

REFERENCES

1. T. F. Rudledge, Acetylenes and Allenes. Reinhold Book Corp., New York, 1969, p. 4.

2. H. F. Schuster and G. M. Coppola, Allenes in Organic Synthesis. JohnWiley, New York, 1984.

3. M. V. Mavrov and V. F. Kucherov, Russ. Chem. Revs. 36, 233 (1967).

4. D. R. Taylor, Chem. Revs. 67, 317 (1967).

5. M. Bertrand, Bull. Soc. Chim. France, 3044 (1968).

6. R. Rossi and P. Diversi, Synthesis, 25 (1973).

7. H. Hopf, in The Chemistry of Ketenes, Allenes and Related Compounds (ed. S. Patai). Wiley-

Interscience, New York, 1980, p. 779.

8. J.-L. Moreau in the same volume.

9. M. Murray, in Houben-Weyl, Methoden der Organischen Chemie, Band 5/2a. Thieme-Verlag,

Stuttgart, 1977.

10. L. F. Fieser and M. Fieser, in Reagents for Organic Synthesis, Vol. 1, John Wiley and Sons,

New York, 1967, p. 529.


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