Regulation of stereoselectivity using Lewis acid in the cyclization of allenic aldehydes catalyzed by palladium complex

[GRAPHICS] A highly diastereoselective synthesis of 3 is achieved from the reaction of 1 with hexamethylditin catalyzed by palladium complex in the presence of 20 mol % tris(pentafluorophenyl)borane as a Lewis acid additive for a reversal of diastereoselectivity, whereas 2 is formed in the absence of Lewis acid additive. The method described herein is successful with various substrates 1 in good yields and high levels of diastereoselectivity.