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Revised Structure of a Purported 1,2-Dioxin: A Combined Experimental and Theoretical Study

Supporting Info

Eric Block,*^† Zhixing Shan,^† Richard S. Glass,^‡ and Jürgen Fabian^§

Departments of Chemistry, State University of New York at Albany, Albany, New York 12222, The University of Arizona, Tucson, Arizona 85721, and Technische Universitt Dresden, D-01062 Dresden, Germany eb801@albany.edu

J. Org. Chem., 2003, 68 (10), pp 4108–4111

DOI: 10.1021/jo034305i

Publication Date (Web): April 16, 2003

In papers with more than one author, the asterisk indicates the name of the author to whom inquiries about the paper should be addressed.

†

State University of New York at Albany.

‡

University of Arizona.

Technische Universität Dresden.

Abstract

3,6-Bis(p-tolyl)-1,2-dioxin (1g) was suggested by Shine and Zhao as a product in an electron-transfer (ET) photochemical reaction. This photoproduct is instead shown to be (E)-1,4-di-p-tolylbut-2-ene-1,4-dione ((E)-4a). Ab initio and DFT calculations indicate that ring-closed 1,2-dioxin is thermodynamically far less stable than open-chain but-2-ene-1,3-dione. These calculations indicate that (E)-4a is formed via the cation radical of 1g, which sequentially isomerizes to a novel σ-radical with an O,O 3e bond [(Z)-4a]⁺^•, undergoes ET to give (Z)-4a, and then photoisomerizes to (E)-4a.