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Molecules 2012, 17(2), 1548-1570; doi:10.3390/molecules17021548

Benzoxetes and Benzothietes ¾ Heterocyclic Analogues of Benzocyclobutene

Institute of Organic Chemistry, University of Mainz, Duesbergweg 10-14, D-55099 Mainz, Germany
Received: 7 December 2011 / Revised: 13 January 2012 / Accepted: 17 January 2012 / Published: 7 February 2012
(This article belongs to the Special Issue Heterocycles)
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Abstract

Benzo-condensed four-ring heterocycles, such as benzoxetes 1 and benzothietes 3 represent multi-purpose starting compounds for the preparation of various higher heterocyclic ring systems. The thermal or photochemical valence isomerizations between the benzenoid forms 1,3 and the higher reactive o-quinoid structures 2,4 provide the basis for the synthetic applications. On the other hand, this valence isomerization impedes in particular the generation and storage of 1 because the thermal equilibrium 1 2 is completely on the side of 2. Thus, the number of erroneous or questionable benzoxete structures published to date is surprisingly high. On the contrary, the thermal equilibrium 3 4 is on the side of the benzothietes 3, which makes them easily accessible, especially by different flash vacuum pyrolysis techniques. The present article gives a survey of the preparations of 1 and 2, and tries to stimulate their use in synthetic projects. Naphtho-condensed and higher condensed compounds and compounds with an exocyclic C=O or S=O double bond (lactones, thiolactones, sulfoxides and sulfones) are not covered in this article.
Keywords: cycloaddition; flash-vacuum-pyrolysis; photochemistry; ring closure; ring opening cycloaddition; flash-vacuum-pyrolysis; photochemistry; ring closure; ring opening
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This is an open access article distributed under the Creative Commons Attribution License (CC BY 3.0).

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Meier, H. Benzoxetes and Benzothietes ¾ Heterocyclic Analogues of Benzocyclobutene. Molecules 2012, 17, 1548-1570.

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