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Computational Studies on Reaction Mechanisms and Origin of Stereoselectivity in the [1,3]‐Rearrangement of Ene‐Aldimines
Author(s) -
Momiyama Norie,
Honda Yasushi,
Suzuki Toshiyasu,
Jongwohan Chanantida
Publication year - 2021
Publication title -
asian journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.846
H-Index - 44
eISSN - 2193-5815
pISSN - 2193-5807
DOI - 10.1002/ajoc.202100302
Subject(s) - aldimine , chemistry , sigmatropic reaction , ene reaction , stereoselectivity , transition state , protonation , stereochemistry , computational chemistry , catalysis , organic chemistry , ion
The mechanism of Brønsted 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.