Theoretical Study On Rh-Catalyzed Cycloadditions Of Vinylaziridines With Allenes

The transition metal-catalyzed cycloadditions provide one of the most important protocles for the systhesis of carbo-and heterocycles.In this thesis,the rhodium-catalyzed intermolecular[3+2]cycloadditions of vinylaziridines with allenes were investigated by means of density functional theory(DFT)calculations,which represent an efficient method for the synthesis of biologically and pharmaceutically relevant chiral methylene pyrrolidines.The computations show that the Rh-allyl complex was formed through an initial C-N oxidative addition.The subsequent proximal C=C bond insertion of allene into the Rh-N bond/C(sp~2)-C(sp~3)reductive elimination or the distal-insertion of allene into the Rh-C bond led to the formation of 3-methylene-pyrrolidine products or 2-methylene-pyrrolidine products,respectively.The calculations reproduced well the experimentally observed high regio-,E/Z,and diastereo-selectivity.In particular,the substituent-controlled proximal/distal selectivity is mainly due to the significant impact of the substituent on the proximal-insertion of allene into the Rh-N bond.The calculations show that for the reactions with N-alleneamines,the proximal-insertion of allene into the Rh-N bond can be significantly promoted by the amine substituent because of the stabilization effect of the lone electron pair of the N atom on the developing positive charge,leading to the 3-methylene-pyrrolidine products.On the other hand for the reactions with general allenes,without such an effect the proximal-insertion of allene into the Rh-N bond is less favorable than the distal-insertion of allene into the Rh-C bond,which thus enables the selectivity switch to form the 2-methylene-pyrrolidine products.Finally,the high E/Z and diastereo-selectivity is rationalized in terms of the steric repulsion between the allene and the Rh-allyl moiety in the corresponding transition states.The results will provide important implications for a better understanding of related reactions.