ALPHA-DEPROTONATED ALLYL ETHERS - CONFORMATIONAL MOBILITY AND CONFORMATIONAL PREFERENCES

tert-Butyllithium is best suited to accomplish a hydrogen/metal exchan ge at the alpha-position of alpha-alkyl branched allyl ethers. Rapid t orsional equilibration occurs at the gamma-terminus of the deprotonate d allyl unit while the alkoxy group at the alpha-site has to occupy th e exo position in order to minimize steric repulsions. The introductio n of an alkoxy group into the terminal position of a gamma-branched 2- alkenyllithium lowers the barrier to torsional isomerization slightly (by a few kcal/mol). (C) 1998 Elsevier Science Ltd. All rights reserve d.