Rh(I)-Catalyzed [5+2]/[2+2] Cycloaddition Cascade to Access a Cyclobutane-Fused [4-5-6-7] Tetracyclic Framework

A Rh(I)-catalyzed [5 + 2]/[2 + 2] cycloaddition cascade has been developed to afford a complex and highly strained [4-5-6-7] tetracyclic framework in good yields and excellent diastereoselectivities. During this transformation, three rings, three C-C bonds, and four contiguous stereocenters were formed efficiently. Mechanistically, the rare sterically congested multisubstituted cyclobutanes are constructed readily through Michael addition and a Mannich reaction cascade. [GRAPHIC]