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.

Automated summary

A rhodium(III)-catalyzed asymmetric reductive cyclization was reported for alpha,beta-unsaturated compounds tethered with cyclohexadienone, leading to cis-bicyclic frameworks with good yields and enantioselectivities. The role of ring strain in controlling regioselectivity and favoring 5,6-bicyclic products was also demonstrated by DFT calculations.