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Benzoxetes and Benzothietes - Heterocyclic Analogues of Benzocyclobutene

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-qu...

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Autor principal: Meier, Herbert
Formato: Online Artículo Texto
Lenguaje:English
Publicado: MDPI 2012
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6268305/
https://www.ncbi.nlm.nih.gov/pubmed/22314379
http://dx.doi.org/10.3390/molecules17021548
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author Meier, Herbert
author_facet Meier, Herbert
author_sort Meier, Herbert
collection PubMed
description 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.
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spelling pubmed-62683052018-12-10 Benzoxetes and Benzothietes - Heterocyclic Analogues of Benzocyclobutene Meier, Herbert Molecules Review 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. MDPI 2012-02-07 /pmc/articles/PMC6268305/ /pubmed/22314379 http://dx.doi.org/10.3390/molecules17021548 Text en © 2012 by the authors; licensee MDPI, Basel, Switzerland. http://creativecommons.org/licenses/by/3.0/ This article is an open-access article distributed under the terms and conditions of the Creative Commons Attribution license (http://creativecommons.org/licenses/by/3.0/).
spellingShingle Review
Meier, Herbert
Benzoxetes and Benzothietes - Heterocyclic Analogues of Benzocyclobutene
title Benzoxetes and Benzothietes - Heterocyclic Analogues of Benzocyclobutene
title_full Benzoxetes and Benzothietes - Heterocyclic Analogues of Benzocyclobutene
title_fullStr Benzoxetes and Benzothietes - Heterocyclic Analogues of Benzocyclobutene
title_full_unstemmed Benzoxetes and Benzothietes - Heterocyclic Analogues of Benzocyclobutene
title_short Benzoxetes and Benzothietes - Heterocyclic Analogues of Benzocyclobutene
title_sort benzoxetes and benzothietes - heterocyclic analogues of benzocyclobutene
topic Review
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6268305/
https://www.ncbi.nlm.nih.gov/pubmed/22314379
http://dx.doi.org/10.3390/molecules17021548
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