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Reaction of a Cyclic Phosphonium Ylide with α,β-Unsaturated Thioesters

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journal contribution
posted on 16.07.1999, 00:00 by Narumi Kishimoto, Tetsuya Fujimoto, Iwao Yamamoto
The tandem Michael−intramolecular Wittig reactions of a five-membered cyclic phosphonium ylide (2) with α,β-unsaturated thioesters afforded cycloheptene derivatives 4ag in 29−58% yield. The reaction proceeded via a rigid phosphabicyclic intermediate and supplied the cycloheptene derivatives with high stereoselectivity. On the other hand, although the reaction using S-cyclohexyl cyclopentenethiocarboxylate 5a as a substrate gave a 1:1 mixture of cis and trans adducts of the corresponding hydroazulene derivatives, the reaction of S-tert-butyl cyclopentenethiocarboxylate 5b gave cis-adduct as a major product (cis:trans =17:3).