The boron-mediated ketone–ketone aldol reaction

The first examples of the directed, boron-mediated aldol reaction between different ketones are presented. Transformation of a variety of ketones to their corresponding boron enolates with Chx2BCl/Et3N, followed by reaction with acceptor ketones in diethyl ether, and oxidation of the resultant boron aldolate (H2O2, MeOH/pH 7 buffer), provided the aldol addition products. The reaction was most facile when cyclic ketones were used, with the highest yields obtained for the reaction of boron enolates with cyclohexanone as the acceptor.