Synthesis of tri-substituted vinyl boronates via ruthenium-catalyzed olefin cross-metathesis

Tri-substituted vinyl pinacol boronates, which are key reactive intermediates in a variety of transformations, are synthesized using ruthenium-catalyzed olefin cross-metathesis of alpha-substituted vinyl boronates and various alkenes. Cross-metathesis of 2-isopropenyl pinacol boronate proceeds with moderate yield and high Z-selectivity when sterically unhindered cross partners are used. Cross-meta thesis of vinyl boronates that possess alpha-substitution larger than a methyl group is also achieved. Yield and Z-selectivity are lower in these cases, and the success of a cross-metathesis reaction is highly dependent oil the steric bulk surrounding the double bond of the alpha-substituted vinyl boronate. (C) 2004 Elsevier Ltd. All rights reserved.