styrene + DMSO --very strong base (hydride)--> allylbenzene
The Addition of Dimethyl Sulfoxide Anion to Olefins and the Pyrolysis of Sulfoxides
Cheves Walling and Laszlo Bollyky
JOC 29, 2699 (1964)
Abstract
Base-catalyzed additions of aryl-conjugated olefins, styrene, and 1,1-diphenylethylene to dimethyl sulfoxide occur rapidly at room temperature and give the corresponding methyl 3-arylpropyl sulfoxides in almost quantitative yield. The reaction fails with aliphatic olefins, but occurs with molecules such as allylbenzene which presumably isomerize before addition. The resulting sulfoxides decompose thermally below 200C, giving quantitative yields of 3-arylpropenes with no double bond isomerization. The kinetics of sulfoxide decomposition in diglyme solution have been studied briefly. Decompositions are first order with half-lives (for aliphatic sulfoxides) of 10-30 hr. at 145C, and the reaction should be of general synthetic value.
Experimental
Reagents were commercial materials unless noted, freshly distilled before use. Dimethyl sulfoxide was distilled from CaH2 under reduced pressure and contained not more than 0.001% water by Karl Fischer titration.
Di-n-dodecyl sulfoxide was prepared by treating 1 g. of dodecyl sulfide in 15 ml. of t-butyl alcohol with 0.35 ml. of 30%, H2O2 in 10 ml. of t-butyl alcohol and stirring for 60 hr. at room temperature. The product was recrystallized from ether with m.p. 88.5-89C, yield 97.5%.
The preparations of other sulfoxides are described below.
Addition of Dimethyl Sulfoxide to 1,1-Diphenylethylene.
The dimethyl sulfoxide anion was prepared by dissolving 1 mole of sodium hydride in 400 ml. of dimethyl sulfoxide. One equivalent of 1,l-diphenylethylene was added at 25C; the mixture was quenched with water, extracted with ether, and dried; and the methyl 3,3-diphenylpropyl sulfoxide was recrystallized from 3:1 ether-hexane. The product, m.p. 70-71C.
When the crude sulfoxide from a similar experiment was distilled under reduced pressure at 150-200°C, 3,3-diphenyl-l-propene, characterized as described earlier, (9) was obtained in a 96% over-all yield. Other experiments listed in Table I were carried out similarly, except that, when gas-liquid chromatography (g.l.c.) was used for analysis, the extracted sulfoxide solution was injected directly into the g.l.c. instrument and underwent immediate pyrolysis in the injector block which was maintained at 250C. The identifications of diphenylmethane and 1,1-diphenylcyclopropane were made as in our previous paper.(9)
Addition of Dimethyl Sulfoxide to Styrene.
Addition to styrene was carried out in the same manner under conditions shown in Table II. The intermediate methyl 3-phenylpropyl sulfoxide, m.p. 43-44C, had the expected infrared and n.m.r. spectra.
Pyrolysis of the crude sulfoxide gave allylbenzene, identified by infrared and n.m.r. spectra and g.l.c. retention time, and a small amount of 3,5-diphenyl-l-pentene, identified by infrared spectrum.
Addition of Dimethyl Sulfoxide to Allylbenzene.
Addition to allylbenzene was carried out in the same manner under the conditions indicated. The methyl 3-phenyl-2-methylpropyl sulfoxide, m.p. 80.5-81C, had the expected infrared and n.m.r. spectra.
Pyrolysis gave 3-phenyl-2-methylpropene in 92% yield, idcntified by infrared and n.m.r. spectra and index of refraction, n 23 D ~ 1.5072, lit. 1.5075.
Table II: Addition of DMSO to other Olefins
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Styrene
Temp: 43C Time:0.5h Base:1.0
Yeild: Allylbenzene 62% (3,5 diphenyl)-1-pentene 28%
Styrene
Temp: 25C Time:0.3h Base:0.22
Yeild: Allylbenzene 71% (3,5 diphenyl)-1-pentene 19%
Styrene
Temp: 25C Time:0.3h Base:2.2
Yeild: Allylbenzene 88% (3,5 diphenyl)-1-pentene 2%
Note: Slow addition of dilute styrene to basic solution.
Allylbenzene
Temp: 25C Time:0.5h Base:1.0
Yeild: 3-phenyl-2-methylpropene 92%
3,3-Diphenylpropene
Temp: 70C Time:2.5h Base:1.0
Yeild: diphenylmethane 50% 3,3-diphenyl-2-methylpropene 30%
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Base:(Moles/mole of olefin)
(9) C. Walling and L. Bollyky, JOC, 28, 256 (1963).
