A density functional theory study of the mechanism of isomerization of 2-aryl-2H-azirines to 2,3-disubstituted indoles by FeCl2 and Rh2(O2CCF3)4

Abstract

A systematic DFT study was performed to examine the isomerization of 2-aryl-2H-azirines to 2,3-disubstituted indoles by FeCl₂ and Rh₂(O₂CCF₃)₄. The results indicate that the isomerization of 2-aryl-2H-azirines mainly proceeds through a stepwise mechanism and the Rh₂(O₂CCF₃)₄ exhibits higher catalytic performance than FeCl₂. Investigation of the magnetic properties suggests that the C–N bond formation step is pseudoelectrocyclization for the FeCl₂-catalyzed system. The calculations show that a water-catalyzed 1,2-H shift for the FeCl₂-catalyzed system adopts a proton-transport catalysis strategy, in which chlorine atom coordination to the iron center is critical because it acts as a proton acceptor. When a molecule of water is involved in the Rh₂(O₂CCF₃)₄-catalyzed reaction, the 1,2-H shift is significantly promoted, so that the rate-determining step becomes the ring opening of 2-aryl-2H-azirine. In addition, we studied the catalytic activity of Fe(OAc)₂ and CuCl.