Stereoselective syntheses of 1,2-dialkyl-1-phenyl cyclopentanes involving intramolecular carbolithiation of alpha-thioalkenes

2-Ethyl-1-methyl-1-phenyl cyclopentane, unavailable by butyllithium-promoted carbocyclisation of the corresponding alkenyl selenide, has been synthesized from 6-methylseleno-6-phenyl-1-phenylthio-1-heptene and 7-methylseleno-7-phenyl-2-phenylthio-2-octene with high stereocontrol at all the three stereogenic centers. Depending upon the solvent used, the derivative in which the methyl- and the phenylthiomethyl groups are cis (in THF) or trans (in pentane) to each other are formed selectively. Copyright (C) 1996 Elsevier Science Ltd