Computational Studies on Reaction Mechanisms and Origin of Stereoselectivity in the [1,3]-Rearrangement of Ene-Aldimines

The mechanism of Bronsted acid-initiated formal [1,3]-rearrangement was rationalized using density functional theory (DFT) calculations. The computed mechanism comprises I) fragmentation: (a) imino-nitrogen protonation, (b) proton transfer to olefin, (c) 1,2-shift, and (d) C-C bond cleavage, and II) product formation: (e) methylene addition, (f) azonia-[3,3]-sigmatropic rearrangement, and (g) methylene elimination. The ene-aldimine fragmentation to the 2-azaallenium cation was found to be a highly reactive intermediate and the real catalyst species. The stereoselectivity for asymmetric formal [1,3]-rearrangement of optically pure ene-aldimine is in good agreement with chair transition state of azonia-[3,3]-sigmatropic rearrangement step and is supported by DFT calculation. Our computational study provides important mechanistic insights for ene-aldimine rearrangements and guides the design of chiral catalysts for rearrangement process.

Automated summary

The mechanism of Bronsted acid-initiated formal [1,3]-rearrangement was rationalized using density functional theory (DFT) calculations, revealing a highly reactive intermediate and the real catalyst species. The computational study provided important mechanistic insights and guided the design of chiral catalysts for rearrangement process.