Desulphuration of sulphur bridged hexahydrotriazines: ring contraction to imidazolidines

Abstract

Raney nickel desulphuration of 6-aryl-2,3-bis(methoxycarbonyl)-1,4-diphenyl-7-thia-2,3,6-triazanorbornane-5-ones (1a,b) yielded mainly 3-aryl-1-benzoyl-5-(methoxycarbonylamino)-5-phenylimidazolidine-2,4-diones (3a,b). A mechanism which involves six alternating ring-opening and ringclosure steps is suggested. Evidence in favour of this unusual pathway include the following: (a) structure of the minor products (4). (b) Desulphuration of the 6-benzyl derivative (1c), which allowed isolation of the intermediate (11c). (c) Desulphuration of the analogous sulphur bridged pyridone (15), which gave the dihydropyridone (17). Structures (3b), (11c), and (17) were confirmed by X-ray analyses.