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 γ‐chlorocarbanions. Because in these cases intramolecular 1,3‐substitution by a SN2′ mechanism leading to vinylcyclopropanes is a relatively slow process these carbanions can be efficiently trapped by active electrophilic reagents such as aldehydes. Subsequent intramolecular SN2′ 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. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) Carbanions of 1‐chloro‐5‐(phenylsulfonyl)pent‐2‐enes can be considered as vinylogues of γ‐halocarbanions. They undergo intramolecular SN2′ 1,3‐substitution and 1,5‐elimination to produce 2‐(phenylsulfonyl)‐1‐vinylcyclopropanes and 1‐(phenylsulfonyl)penta‐2,4‐dienes. They also add rapidly to aromatic aldehydes to produce the corresponding 2‐aryl‐3‐(phenylsulfonyl)‐5‐vinyltetrahydrofurans.