Phosphathiahelicenes: Synthesis and Uses in Enantioselective Gold Catalysis

Enantiomerically pure thiahelicenes displaying a terminal phosphole unit and a stereogenic phosphorus center have been prepared by oxidative photocyclization of a diaryl-olefin precursor. Starting from one of these phosphathiahelicene oxides, the corresponding trivalent phosphine-Au-I complex is obtained with complete diastereoselectivity. It affords a new, excellent precatalyst for the enantioselective cycloisomerization of N-tethered enynes (up to 96% ee).