1,2-stereochemical induction in the Pd^II-catalyzed conjugate addition of boronic acids

Abstract

Palladium(II) catalysis has been used in the substrate-controlled 1,2-chiral induction of the conjugate addition of boronic acids to enantiopure α,β-unsaturated ketones and esters without competition from the Mirozoki-Heck reaction. Bedford's palladacycle was found to control the stereoselectivity without the need for additional chiral ligands. We report that the Pd^II-catalyzed conjugate addition reaction between boronic acids and acyclic ketones or esters that bear a hydroxyl substituent at their γ-position (glyceraldehyde derivatives) can afford high levels of anti stereoselection, comparable to those reported previously using more expensive Rh^I catalysts. On the other hand, high levels of syn stereoselectivity were observed with acyclic esters that bear an amino substituent at their γ-position (serine derivatives). In this case, the levels of stereoselection could be enhanced by using cyclic derivatives derived from Garner's aldehyde.