Thermal and microwave assisted reactions of 2,5-disubstituted thienosultines with [60]fullerene: non-Kekule biradicals and self-sensitized oxygenation of the cycloadduct

Abstract

Refluxing an o-dichlorobenzene solution of 2,5-disubstituted thienosultines 10a-f with [60]fullerene for 2-24 h gave both 1:1 and 2:1 cycloadducts in 37-79% isolated yields. The reaction was highly accelerated by microwave irradiation giving comparable yields of cycloadducts. Sultines 10a-f underwent cheletropic extrusion of SO2 to form the corresponding non-Kekule biradical intermediates 11a-f, which were subsequently trapped by [60]fullerene to form corresponding cycloadducts. The activation energy barriers (DeltaG(c)(not equal)) determined for the boat-to-boat inversion of these 4',5',6',7'-tetrahydrobenzo[c]thieno-[5',6':1,2][60]fullerene adducts 12a-f were found to be in the range of 13.5-14.8 kcal/mol. Unexpectedly, one of the monoadduct 12a was found to be labile when kept in air under ambient light. Two new products 15 (a sulfine-enone) and 16 (an endione) were isolated from the decomposed 12a and were found to derive from self-sensitized singlet oxygen reaction on the 2,5-dimethylthieno moiety of 12a. (C) 2004 Elsevier Ltd. All rights reserved.