Reactions of Carbanions of 1-Chloro-5-(phenylsulfonyl)pent-2-enes: Synthesis of Vinyl-Substituted Tetrahydrofurans

The carbanions of (E)- and (Z)-1-chloro-5-(phenylsulfonyl)pent-2-enes can be considered as vinylogues of gamma-chlorocarbanions. Because in these cases intramolecular 1,3-substitution by a S(N)2' mechanism leading to vinylcyclopropanes is a relatively slow process these carbanions can be efficiently trapped by active electrophilic reagents such as aldehydes. Subsequent intramolecular S(N)2' 1,5-substitution of the aldol anions produced gives vinyl-substituted tetrahydrofurans. Thus, an efficient method for the synthesis of 2,3-disubstituted-5-vinyltetrahydrofurans has been elaborated. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)