Rhodium-Catalyzed Asymmetric Synthesis of 3,4-Dihydrocoumarins

Significance

An interesting approach to the synthesis of 3,4-dihydrocoumarins is reported based on a rhodium-catalyzed asymmetric cascade reaction. The cascade is very effective for six-membered rings, though the enantioselectivities and yields are lower for seven-membered rings. Deuterium labeling studies were used to probe the mechanism and identified a 1,4-rhodium shift, which was exploited to allow conjugate addition by the aryl-rhodium species.