Palladium(0)-catalyzed cis-selective alkylative and arylative cyclization of alkynyl enones with organoboron reagents

A palladium(0)-tricyclohexylphosphine catalyzes cis-selective alkylative and arylative cyclization of alkyne-containing electron-deficient alkenes with organoboron reagents to provide five- or six-membered rings with exo tri- or tetra-substituted alkenes. The opposite stereoselectivity to that for the alkyne-aldehyde cyclization using the same reagents would result from palladacycle-forming oxidative addition of the substrates to the Pd-0 catalyst followed by transmetalation with the boron reagents, protonation, and reductive elimination. The functional group compatibility, availability, stability, and non-toxicity of the reagents, and the fact that no additives are needed make the process more practical than the Ni-0-catalyzed cyclization with organozinc reagents. (C) 2008 Elsevier Ltd. All rights reserved.