Reaction of 3,3,5,5-Tetramethylthiolane-2,4-dithione with Benzyne: Novel Formation of Benzodithiole

Abstract

Reaction of 3,3,5,5-tetramethylthiolane-2,4-thione with benzyne gave a new type of benzodithiole in 78% yield.Dithioester's thiocarbonyl group initially attacked benzyne to afford the corresponding betaine, which finally rearranged to give benzodithiole.On the other hand, reaction of cyclic dithiolactone with benzyne recovered the starting dithiolactone in almost quantitatively.The chemistry of thiones has been studied extensively in recent years because of their unique and interesting properties. 1 Benzyne is a reactive intermediate that reacts with many dienes to afford the corresponding cycloadducts. 2Because of our ongoing interest in the exploration of reactive benzynes for the synthesis of functionalized S-heterocycles, we attempted the synthesis of benzothietes and benzothianes. 3 The results have prompted us to investigate the reaction of dithioesters with benzyne, which is reported herein.We first attempted the reaction of simple dithioesters with benzyne.o-Trimethylsilylphenyl trifluoromethanesulfonate was used as the benzyne precursor. 4Treatment of benzyl dithio-pchlorobenzoate (1a) 5 with benzyne led to the recovery of the starting dithioesters (Scheme 1).We next attempted the reaction of cyclic dithioester.Recently, we have reported the synthesis of 3,3,5,5-tetramethylthiolane-2,4-thione (2) by thermolysis of 2,2,4,4-tetramethylcyclobutane-1,3-dione with tetraphosphorus decasulfide (Scheme 2). 6