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Thia-Diels–Alder reactions of hetaryl thioketones with nonactivated 1,3-dienes leading to 3,6-dihydro-2H-pyrans: evidence for a diradical mechanism


Mloston, Grzegorz; Grzelak, Paulina; Linden, Anthony; Heimgartner, Heinz (2017). Thia-Diels–Alder reactions of hetaryl thioketones with nonactivated 1,3-dienes leading to 3,6-dihydro-2H-pyrans: evidence for a diradical mechanism. Chemistry of Heterocyclic Compounds, 53(5):518-525.

Abstract

Dihetaryl thioketones possessing thiophen-2-yl and selenophen-2-yl rings react as ''superdienophilic'' reagents with nonactivated 1,3-dienes such as 2,3-dimethylbuta-1,3-diene, cyclopentadiene, and mixtures of isomeric hexa-2,4-dienes to produce the expected 2H-thiopyrans in moderate to excellent yields. In the latter case, the corresponding cis-2,2-dihetaryl-3,6-dimethyl-3,6-dihydro-2H-thiopyrans are formed as the sole products in a stereoconvergent thia-Diels–Alder reaction. A stepwise mechanism via delocalized diradical intermediates is postulated to rationalize the observed reaction course. Treatment of 4,5-dimethyl-2,2-di(thiophen-2-yl)-3,6-dihydro-2H-thiopyran with excess of m-CPBA at room temperature leads to the oxidation of the C=C bond and the sulfur atom in the six-membered ring.

Abstract

Dihetaryl thioketones possessing thiophen-2-yl and selenophen-2-yl rings react as ''superdienophilic'' reagents with nonactivated 1,3-dienes such as 2,3-dimethylbuta-1,3-diene, cyclopentadiene, and mixtures of isomeric hexa-2,4-dienes to produce the expected 2H-thiopyrans in moderate to excellent yields. In the latter case, the corresponding cis-2,2-dihetaryl-3,6-dimethyl-3,6-dihydro-2H-thiopyrans are formed as the sole products in a stereoconvergent thia-Diels–Alder reaction. A stepwise mechanism via delocalized diradical intermediates is postulated to rationalize the observed reaction course. Treatment of 4,5-dimethyl-2,2-di(thiophen-2-yl)-3,6-dihydro-2H-thiopyran with excess of m-CPBA at room temperature leads to the oxidation of the C=C bond and the sulfur atom in the six-membered ring.

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Department of Chemistry
Dewey Decimal Classification:540 Chemistry
Language:English
Date:June 2017
Deposited On:20 Jun 2017 12:57
Last Modified:16 Jul 2017 05:20
Publisher:Springer
ISSN:0009-3122
Funders:National Science Center (Cracow, PL), Maestro Grant Number: Dec-2012/06/A/ST5/00219
Publisher DOI:https://doi.org/10.1007/s10593-017-2086-9

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