- A hydride transfer reaction from salts of carbanions to activated olefins
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A novel reaction - a β-elimination of a hydride ion from carbanion salts RM (R = Li, MgBr) and R2N-Li+, and its transfer to tetra-substituted activated olefins of the type Ar2C=C(CN)CO2R (R = Me,Et), was studied. Yields of the reduced H--acceptor were used to follow the extent of the H--transfer reaction. A competing Michael addition reaction of RM to the activated olefin also took place. The effects of the solvation properties of the solvent, the reaction temperature, the positive counter-ion, and of various structural features of the H--donor and the H--acceptor, were studied. The structural factors associated with both reactants, played a critically significant role due to the bimolecularity of the reaction. A benzyl substituent at C(β) of RM, a methine-type β-carbon, or a small size of R of RM, resulted in a relatively high extent of the H--transfer reaction. It is suggested that the presently studied β-elimination of a hydride ion takes place by a bimolecular E2cB-type mechanism.
- Feit, Ben-Ami,Shapira, Sarit,Herbst, Amatzya
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- Decarboxylative radical addition to vinylsulphones and vinylphosphonium bromide: Some further novel transformations of geminal (pyridine-2-thiyl) phenylsulphones
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Irradiation of O-acyl derivatives 1 of N-hydroxy-2-thiopyridone with visible light in the presence of phenyl vinyl sulphone or vinyl triphenylphosphonium bromide leads to the corresponding adducts 8 and 9 which can undergo a wide variety of further transformations.
- Barton,Boivin,Crepon nee da Silva,Sarma,Togo,Zard
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p. 7091 - 7108
(2007/10/02)
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- RADICAL ADDITION TO VINYL SULPHONES AND VINYL PHOSPHONIUM SALTS
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Alkyl radicals, derived from decarboxylation of carboxylic acids, add readily to phenyl vinyl sulphone and vinyl phosphonium bromide.The adducts may be further converted into a variety of useful synthetic intermediates.
- Barton, Derek H. R.,Togo, Hideo,Zard, Samir Z.
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p. 6349 - 6352
(2007/10/02)
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- 78. Ueber den Anteil sigmatroper 1,5-Wanderung von Kohlenwasserstoffgruppen bei der thermolytischen Skelettisomerisierung 5,5-disubstituierter 1,3-Cyclohexadiene
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The uncatalyzed skeletal isomerization of 5,5-disubstituted 1,3-cyclohexadienes was investigated with the aim to establish the extent to which sigmatropic 1,5-shifts of hydrocarbon groups are participating in these reactions.Gas phase pyrolysis of 5,5-diethyl-1,3-cyclohexadiene (7) at 460 deg C followed by chloranil aromatization yields only 4percent of 1,3-diethylbenzene resulting from 7 through a 1,5-ethyl migration in the primary reaction step 2,3-Dimethylethylbenzene (56percent) and 1,4-diethylbentene (4percent) are obtained as other C10-compounds.This shows that isomerization proceeds mainly through a sequence of electrocyclic and 1,7-shift reactions.Ethylbenzene (24percent) and other aromatic C8- and C9-hydrocarbons are formed to a considerable extent, indicating that C,C-bond cleavage is a major competing process and that the 1,3-diethylbenzene found is the result of a radical recombination reaction and not of a concerted sigmatropic shift of the ethyl group. 5-Methyl-5-phenyl-1,3-cyclohexadiene (12) yields 3-methylbiphenyl (14) and biphenyl upon thermolysis and aromatization.Through 13C-substitution of the methyl group in 12 it is shown that in solution at 300 deg skeletal isomerization proceeds through electrocyclic and 1,7-H-shift reactions exclusively.In the gas phase at 500 deg 4percent of the isomerization product is formed by a 1,5-shift of a substituent, presumably of the methyl group, through a dissociative mechanism.Thermolysis of 5,5-diphenyl-1,3-cyclohexadiene (22) at 560 deg in the gas phase leads to 1,1-diphenyl-1,3,5-hexatriene (23) and 1-vinyl-4-phenyl-1,2 dihydronaphthalene (24) through electrocyclic reaction steps.In addition a small amount of m-terphenyl is obtained at high conversion of 22.This indicates that sigmatropic 1,5-phenyl migration can participate in product formation only at high temperature and in the absence of other irreversible pathways to stable products.
- Schiess, Peter,Dinkel, Rolf
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p. 801 - 812
(2007/10/02)
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