Studies On Rhodium-Catalyzed [2+2+2] Asymmetric Cyclization Reactions Of 1,6-Enynes And Oxabenzonorbornadienes

The transition metal-catalyzed asymmetric carbocyclizations have been paid close attention to as hot reactions in recent years. Ring frameworks widely distribute in natural products and bioactive molecules. The vast majority of complex molecules contain one or more ring. The transition metal-catalyzed asymmetric carbocyclizations are the most efficient and atom-economic methods to construct ring frameworks because of building one or more rings once. People further focus on the asymmetric carbocyclizations of 1, 6-enynes. 1, 6-enynes can occur in scores of different cyclization reactions as substrates to generate a plurality of different cyclic chiral molecules. Among, some reactions can not only gain higher yield but also display higher enantioselectivity. The carbocyclizations of 1, 6-enynes are so diverse and effective that they can provide effective methods for synthesizing cyclic molecules. It is still a challenging task to develop efficient, high enantioselectivity and wide substrate scope of the asymmetric carbocyclizations of 1, 6-enynes. The transition metal-catalyzed [2+2+2] carbocyclizations of 1, 6-enynes are the most effective and the most valuable methods for synthesizing complex bicyclic molecules by one-step. This reactions have become research hotspot for chiral chemists because they are remarkably atom-economic and environment-friendly and so on.In order to further research for 1, 6-enynes, we applied bomadienes to the [2+2+2] carbocyclizations with 1, 6-enynes. It could provide a new and efficient method for the synthesis of chiral molecules.In the process of studying Rh-catalyzed asymmetric [2+2+2] carbocyclizations, chiral ligand Rh-PHOS was proved to be very efficient. By the using of optimum conditions, the Rh(R)-Xyl-P-PHOS complex could transfrom a range of 1, 6-enynes derivatives and normomadienes to adduct in good yields with high enantioselectivities. The present study showed that catalyst generated from Rh(R)-Xyl-P-PHOS and [Rh(COD)2]BF4 are the most effective chiral catalyst. When this catalyst was used in dioxane solvent, a series of 1,6-enynes could react with normomadienes to provide the cyclopentane products in good yields(up to 62%) with high enantioselectivties(up to 99.9% ee).