Hunig's base and S2Cl2 give the fused 1,4-thiazines 1 and (in the pres
ence of formic acid) 2 and 3, each of which readily extrudes sulfur, s
electively and quantitatively, to give the fused pyrroles 4, 5 and 6 r
espectively; at higher temperatures Hunig's base and S2Cl2 can be conv
erted into the pyrroles in one pot, and the cycloadducts 8 and 10 are
thus readily available in two steps.