Tandem reductive lithiations - Carbanionic cyclizations yielding sulfur stabilized cyclopropyl- and cyclobutylcarbinyllithiums

Reductive lithiation of 1,4- or 1,5-bis(phenylthio)-1-alkenes with an aroma tic radical-anion results in replacement with a lithium atom of only that p henylthio group which is attached to the sp(3) carbon atom. The resulting c arbanion executes an intramolecular nucleophilic addition to the vinyl sulf ide group, usually at -78 degrees C, leading to a phenylthio-stabilized cyc lopropyl- or cyclobutylcarbinyllithium. The substrates were prepared by Wit tig or Peterson olefination of carbonyl compounds which were in turn genera ted by conjugate addition of thiophenol or of the cuprate of a phenylthio-s tabilized carbanion to an alpha,beta-unsaturated carbonyl compound. (C) 199 9 Elsevier Science Ltd. All rights reserved.