An enantioselective synthetic route to atractyligenin using the oxazaborolidine-catalyzed reduction of beta-silyl- or beta-stannyl-substituted alpha,beta-enones as a key step

In this paper, we describe a novel catalytic enantioselective synthetic route to the bicyclic tetraene ester 3, a key intermediate for the synthesis of the naturally occurring adenosine diphosphate transport inhibitor atractyligenin (2). The success of this route depended on the extension of the oxazaborolidine-catalyzed (CBS) reduction of an achiral beta-stannyl-substituted alpha,beta-enone (6c) to form a chiral allylic alcohol and further steps to effect simultaneous transfer of chirality, carbocycle formation, and quaternary stereocenter formation, which led to the triene acid 13. The conversion of 13 to 3 was carried out efficiently by a four-step sequence involving iodolactonization, double elimination, and esterification. The combined use of the CBS reduction of appropriate alpha,beta-enones and Claisen rearrangement provides an important synthetic avenue to many types of natural products containing quaternary stereocenters embedded in cyclic networks.