Theoretical investigation on the rhodium-catalyzed coupling reaction of
ketoxime with 1,3-enynes: [4 + 1] vs. [4 + 2] annulation
Abstract
The mechanisms of rhodium-catalyzed coupling reaction of ketoxime and
1,3-enynes were investigated by employing the density functional theory
(DFT) calculations. Different 1,3-enynes would lead to different
annulation products. Reaction A undergoes five sequential steps (C-H
activation, 1,3-enyne migratory insertion, 1,4-Rh migration,
cyclization, and deprotonation) to lead to [4 + 1] annulation
product. Whereas, due to the electronic effect, the process generating
[4 + 2] product in reaction A is restricted. In contrast, the
electron-withdrawing group of N(Me)2 group in 1,3-enyne would bring
about the [4 + 2] annulation product in reaction B. Our calculated
results indicate that no [4 + 1] annulation product could be
obtained in reaction C, in agreement with the experimental observation
that the cis-allyl hydrogen in 1,3-enyne is crucial for the [4 + 1]
annulation reaction.