Enantioselective Gold(I)-Catalyzed [2+2] Cycloaddition of Allenenes

Significance

The authors report the first transition-metal-catalyzed cycloisomerization of allenenes to provide access to enantioenriched bicyclo[3.2.0] ring systems through use of a chiral biarylphosphine-gold(I) complex. Mechanistic studies indicate that the reaction proceeds through a series of cationic intermediates in accordance with previous reports. When methanol was added, the proposed benzylic cationic intermediate 8 was trapped to yield trans-cyclopentane 4. Thus, in the absence of an external nucleophile, the reaction proceeds through cis-intermediate 10.