Rhodium(Iii)-Catalyzed Asymmetric Reductive Cyclization Of Cyclohexadienone-Containing 1,6-Dienes Via An Anti-Michael/Michael Cascade Process

Ring strain plays an important role in metal-catalyzed cyclization of 1,6-dienes. Herein, we report a rhodium(III)-catalyzed asymmetric reductive cyclization of cyclohexadienone-tethered alpha,beta-unsaturated compounds (1,6-dienes), including alpha,beta-unsaturated ketones, esters, amides, sulfone, and phosphonate. The reactions undergo an unusual anti-Michael/Michael addition process, affording cis-bicyclic frameworks with good to high yields and good diastereo- and enantioselectivities. Furthermore, several transformations of the products and a one-pot preparation of bridged polycyclic structure are also presented. Finally, DFT calculations show that the enantioselectivity is determined by the initial olefin insertion step and that the ring strain controls the overall regioselectivity and favors the formation of 5,6-bicyclic products.