Organic thionitroso compounds

A series of novel N-substituted phthalimide-2-sulplienamides was prepared. The N-aryl analogues were shown to be efficient precursors to thionitrosoarenes. Extension of the methodology to heteroaroraatic and acyl derivatives was unsuccessful, with the exception of 3-thionitroso- pyridine, the first known thionitrosoheteroarene. Thionitrosoarenes are shown to be versatile dienophiles and enophiles. Reactions with various substituted dienes proceeded with high stereoselectivity and some regioselectivity to afford 3,6-dihydro- 1,2-thiazines. Cycloadditions of thionitrosoarenes generated independently from imidosulphurous chloride precursors showed similar selectivities. The mechanism of cycloaddition is discussed in the light of molecular orbital calculations.