An Enantioselective Synthetic Route to Atractyligenin Using the Oxazaborolidine-Catalyzed Reduction of β-Silyl- or β-Stannyl-Substituted α,β-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 β-stannyl-substituted α,β-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 α,β-enones and Claisen rearrangement provides an important synthetic avenue to many types of natural products containing quaternary stereocenters embedded in cyclic networks.