Synthesis of Polycyclic n /5/8 and n /5/5/5 Skeletons Using Rhodium-Catalyzed [5 + 2 + 1] Cycloaddition of Exocyclic-ene-vinylcyclopropanes and Carbon Monoxide.

A rhodium-catalyzed [5 + 2 + 1] reaction of exocyclic-ene-vinylcyclopropanes (exo-ene-VCPs) and CO has been realized to access challenging tricyclic n /5/8 skeletons ( n = 5, 6, 7), some of which are found in natural products. This reaction can be used to build tetracyclic n /5/5/5 skeletons ( n = 5, 6), which are also found in natural products. In addition, 0.2 atm CO can be replaced by (CH 2 O) n as the CO surrogate to achieve the [5 + 2 + 1] reaction with similar efficiency.