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 (chloro)di(cyclohexyl)borane/Et3N, followed by reaction with acceptor ketones in di-Et ether, and oxidn. of the resultant boron aldolate (H2O2, MeOH/pH 7 buffer), provided the aldol addn. 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. The boron-mediated aldol reaction of 1-(phenylmethyl)-4-piperidinone with cyclohexanone gave 3-(1-hydroxycyclohexyl)-1-(phenylmethyl)-4-piperidinone.

Tetrahedron Letters