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Sequential allylation of chiral, nonracemic thiolactam 8 affords clean thio-Claisen [3,3] products 11. The stereoselectivity of the rearrangement was found to be on the order of 10-11:1, with the exo-endo products responsible for the mixture. Addition of hydride or methyllithium-cerium chloride gave clean addition to the thiolactam in the form of its iminium salts 12. Hydrolysis gave 4,4-dialkylcyclohexenones 15, which were cyclized to the cyclopentene derivatives 16 using Grubbs' catalyst.
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Lemieux et al. (1999) studied this question.
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