Why Nature Eschews the Concerted [2 + 2 + 2] Cycloaddition of a Nonconjugated Cyanodiyne. Computational Study of a Pyridine Synthesis Involving an Ene–Diels–Alder–Bimolecular Hydrogen-Transfer Mechanism
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Danheiser_Why nature eschews.pdf
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Author(s)
Lan, Yu
Houk, K. N.
Danheiser, Rick Lane
Date Issued
December 2011
Journal
Journal of Organic Chemistry
Publisher
American Chemical Society (ACS)
Citation
Lan, Yu, Rick L. Danheiser, and K. N. Houk. “Why Nature Eschews the Concerted [2 + 2 + 2] Cycloaddition of a Nonconjugated Cyanodiyne. Computational Study of a Pyridine Synthesis Involving an Ene–Diels–Alder–Bimolecular Hydrogen-Transfer Mechanism.” The Journal of Organic Chemistry 77, no. 3 (February 3, 2012): 1533-1538.
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Author's final manuscript
Abstract
An intramolecular formal metal-free intramolecular [2 + 2 + 2] cycloaddition for the formation of pyridines has been investigated with M06-2X and B3LYP density functional methods, and compared to the experimentally established three-step mechanism that involves ene reaction–Diels–Alder reaction–hydrogen transfer. The ene reaction of two alkynes is the rate-determining step. This is considerably easier than other possible mechanisms, such as those involving an ene reaction of an alkyne with a nitrile, a one-step [2 + 2 + 2] cycloaddition, or a 1,4-diradical mechanism. The relative facilities of these processes are analyzed with the distortion-interaction model. A bimolecular hydrogen-transfer mechanism involving a radical-pair intermediate is proposed rather than a concerted intramolecular 1,5-hydrogen shift for the last step in the mechanism.
MIT Department
Massachusetts Institute of Technology. Department of Chemistry
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DOI of Published Version
https://doi.org/10.1021/jo202424n
