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Experimental and Computational Studies on the [3,3]- and [3,5]- Sigmatropic Rearrangements of Acetoxycyclohexadienones: A Nonionic Mechanism for Acyl Migration.
- Source :
-
Journal of the American Chemical Society . 9/25/2013, Vol. 135 Issue 38, p14438-14447. 10p. - Publication Year :
- 2013
-
Abstract
- Flash vacuum pyrolysis studies of substituted 6- acetoxy-2,4-cyclohexadienones (3 and 10) from 300 to 500 °C provide strong experimental evidence that direct [3,5]- sigmatropic rearrangements in these molecules are favored over the more familiar [3,3]-sigmatropic rearrangements. The preference holds when the results are extrapolated to 0.0% conversion, indicating that this is a concerted process. Pyrolysis of 6,6-diacetoxy-2-methyl-2,4-cyclohexadienone (9) at 350 °C gives a modest yield of the initial [3,5]-sigmatropic rearrangement product, 2,6-diacetoxy-6-methyl-2,4-cyclohexadienone (11). Qualitative arguments and electronic structure theory calculations are in agreement that the lowest energy pathway for each [3,5]-sigmatropic rearrangement is via an allowed, concerted pseudopericyclic transition state. The crystal structures of compounds 3, 9, and 10 prefigure these transition states. The selectivity for the [3,5] products increases with an increasing temperature. This unexpected selectivity is explained by a concerted, intramolecular, and pseudopericyclic transition state (TS-5) that forms a tetrahedral interemediate (ortho-acid ester 4'), followed by similar ring openings to isomeric phenols, which shifts the equilibrium toward the phenols from the [3,5] (but not the [3,3]) products. [ABSTRACT FROM AUTHOR]
Details
- Language :
- English
- ISSN :
- 00027863
- Volume :
- 135
- Issue :
- 38
- Database :
- Academic Search Index
- Journal :
- Journal of the American Chemical Society
- Publication Type :
- Academic Journal
- Accession number :
- 90485310
- Full Text :
- https://doi.org/10.1021/ja4077364