The synthesis of bicyclic 1,2,3,4-tetrahydro-1,4-benzodiazepin-5-ones from 2-(o-nitrobenzyl)-1,2-thiazine-1-oxide precursors

Sulfinylation of o-nitrobenzamide and subsequent hetero Diels–Alder reaction gave a series of 2-(o-nitrobenzoyl)-1,2-thiazine-1-oxides. The 2-(o-nitrobenzoyl)-1,2-thiazine-1-oxides undergo a ring opening reaction with phenyl magnesium bromide to give allylic sulfoxides, which, after [2,3]-sigmatropic rearrangement and desulfurisation, furnish unsaturated vicinal N-(o-nitrobenzoyl)-1,2-amino alcohols. Oxidation of the alcohol and reductive ring closure gave a series of bicyclic 1,2,3,4-tetrahydro-1,4-benzodiazepin-5-ones, a subset of the ‘privileged’ 1,4-benzodiazepine structure. A 4-hydroxy-1,2,5-benzothiadiazepin-1,1-dioxide was synthesised by the same route starting from o-nitrobenzenesulfonamide.