Understanding diversified chemoseletivities in Rh2(II)-catalyzed intramolecular annulation reactions of diazo and N-Sulfonyl-1,2,3-triazole compounds: A DFT study

Abstract

Computational studies were performed to shed light on the origins of diversified chemoseletivities in Rh2(II)-catalyzed intramolecular annulation reactions of structurally analogous diazo and N-sulfonyl-1,2,3-triazole compounds. For methyl 2-diazo-5-phenylpentanoate (1) and 1-diazo-4-phenylbutan-2-one (3), after the formation of key Rh2(II)-carbenes, the intramolecular cyclization to form norcaradiene intermediates is ready to occur, which could further lead to annulated cycloheptatriene derivatives. Computational results suggest that the step of three-membered ring formation in the generation of a norcaradiene intermediate is considerably sensitive to steric hindrance. For the Rh2(II)-catalyzed intramolecular annulation reaction of ethyl 2-diazo-3-oxo-5-phenylpentanoate (5), bearing two electron-withdrawing groups, the commonly supposed electronic effect, however, may not play an important role in determining the chemoselectivity of 1,2-H migration over the formation of a norcaradiene intermediate. For the Rh2(II)-catalyzed intramolecular annulation of structurally analogous 1,2,3-triazole carbene precursor (7), due to the presence of imino group in the key Rh2(II)-azavinyl carbene intermediate, the feasible intramolecular cyclization in the Rh2(II)-carbene intermediates could be converted to an intramolecular [3+2] cycloaddition in a one-step manner.