Thietan-3-imines, formation

Whereas pyrroles normally undergo substitution at the C-2 position, 1-arylsulfonylpyrroles display a tunable reactivity in Friedel-Crafts acylations, wherein substitution occurs at C-3 in the presence of "hard acids" such as aluminum chloride but mainly at C-2 when catalyzed by weaker acids <81TL4899,81TL4901>. An alternative route to 3-aroylpyrroles 38 has been introduced via irradiation of 1-acetyl- or 1-phenylsulfonylpyrrole (36) with arenethiocarboxamides <96H(43)463>. The proposed mechanism involves formation and scission of a thietane intermediate 37, followed by hydrolysis of the resultant imine. 

Dithiane formation was also observed. N-Methyl-thiophthalimide, N-methyldithiophthalimide and xanthene-9-thione similarly undergo photoaddition to diphenylketene to yield spiro-thietan-2-ones, and thioimides add to diphenyl-N-( -tolyl)keten-imine to give analogous 2-iminothietanes. A detailed examination of the photoaddition of dithioimides to alkenes has establish-... 

---