Reactions of Benzyne with 1,3-Benzodithiole-2-thione and Related Compounds: Formation of Novel Tetracyclic Sulfonium Salts and Their Reactions Leading to Dibenzo-1,3,6,-trithiocin Derivatives

A sulfur ylide intermediate, produced by a 1,3-dipolar cycloaddition of 1,3-benzodithiole-2-thione (5) with benzyne, was successfully trapped by hydrogen chloride to give a novel tetracyclic sulfonium salt, 9aH-9,10-dithia-4b-thioniaindeno[1,2-a]indene chloride (7), in good yield when benzyne was generated by the thermolysis of 2-carboxybenzenediazonium chloride (4). The reaction of ethylene trithiocarbonate with excess 4 provided a convenient one-pot synthesis of 7 in large quantities. The reduction of 7 with NaBH4 gave a novel ring compound, dibenzo[d,g][1,3,6]trithiocin (15), in 95% yield, while alkaline hydrolysis produced the 12-oxide derivative of 15. The treatment of 7 with t-BuOK gave 6,6′-bi(dibenzo[d,g][1,3,6]trithiocinylidene) in 84% yield. Also described are the reactions of benzyne with related compounds of 5.