In this study, we used density functional theory (DFT) to reinvestigate the mechanism proposed by Houk and Zhang et al. (J. Am. Chem. Soc. 2012, 134, 1078) for piperidinone formation through rearrangement of an acetylenic amine N-oxide catalysed by Carbon gold(I) comple
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In this study, we used density functional theory (DFT) to reinvestigate the mechanism proposed by Houk and Zhang et al. (J. Am. Chem. Soc. 2012, 134, 1078) for piperidinone formation through rearrangement of an acetylenic amine N-oxide catalysed by Carbon gold(I) complexes. For this rearrangement, the C-C coupling was proposed to be the rate-determining step with activation energy as high as 33 kcal/mol. Such a barrier seems inconsistent with the fact that the actual reaction proceeds under very mild conditions (0 oC, 1 hr, in CH2Cl2). In the original report, it was proposed that the C-C coupling takes place via a mechanism which we called “side-on addition”. Interestingly, we found that the C-C coupling step becomes energetically more favourable if it occurs via another mechanism called “back-side addition”. We explored the effect of different Carbon ligands on all conceivable steps of the catalytic reaction and found that while the other steps are not highly sensitive to the Carbon identity, the C-C coupling one shows a considerable degree of dependency; the more electron-donating the Carbon ligand, the lower the rate-limiting step barrier
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