Synthesis of (-)-cubebol by face-selective platinum-, gold-, or copper-catalyzed cycloisomerization: evidence of chirality transfer and mechanistic insights.

We describe in detail a direct, stereoselective synthesis of (-)-cubebol based on a Pt-, Au-, or Cu-catalyzed cycloisomerization in which control of the configuration of the propargylic center is essential for the facial selectivity. In addition, we show that cycloisomerization reactions of enantioenriched propargyl pivalates occur with substantial chirality transfer. We confirm a mechanism by means of cyclization followed by an [1,2]-acyl migration for the Pt- and the Au-catalyzed cycloisomerization. So far, no evidence supports that the Cu-catalyzed cycloisomerization follows the same reaction course.