The photochemical C2-C6 cyclization of enyne-allenes: Interception of the fulvene diradical with a radical clock ring opening

Bucher, G. , Mahajan, A. A. and Schmittel, M. (2009) The photochemical C2-C6 cyclization of enyne-allenes: Interception of the fulvene diradical with a radical clock ring opening. Journal of Organic Chemistry, 74(16), pp. 5850-5860. (doi:10.1021/jo900439x)

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Abstract

The mechanism of the photochemical C2-C6 cyclization of enyne-allenes has been studied through radical clock, intramolecular kinetic isotope effect, and laser flash photolysis (LFP) experiments as well as density functional theory (DFT) and ab initio computations, While the photochemical cyclization of enyne-allenes 1 and 2 furnished ene and Diels-Alder products without any cyclopropyl ring opening, that of 3 carrying the ultrafast diphenylcyclopropylcarbinyl radical clock, afforded products derived from cyclopropyl ring opening. Laser flash photolysis (LFP) studies oil enyne-allene 3 point to an allene triplet excited state (transient A) as it primarily formed short-lived (tau = 430 ns) intermediate. In addition, we have obtained evidence for the forma(ion of it diphenylmethyl-type diradical (transient C, tau = 1.0 mu s) resulting from ring opening of it diphenylcyclopropane ring. C subsequently undergoes a Surprisingly slow (tau = 1.0 mu s) 1,6-hydrogen shift leading to the stable 1,3-diene 6.

Item Type:Articles
Keywords:Benzoenyne-allenes, Bergman cyclization, biradical cyclization, computations, cyclization, cycloaddition reactions, cyclopropyl, density, DNA strand cleavage, electron-transfer, formal diels-alder, laser flash photolysis, , mechanism, Myers-Saito reaction, state, substituted cyclopropylcarbinyl radicals
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Bucher, Dr Goetz
Authors: Bucher, G., Mahajan, A. A., and Schmittel, M.
College/School:College of Science and Engineering > School of Chemistry
Journal Name:Journal of Organic Chemistry
ISSN:0022-3263
ISSN (Online):1520-6904
Published Online:14 July 2009

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