Reductive cyclization of carbohydrate 2-nitrophenylhydrazones to chiral functionalized 1,2,4-benzotriazines and benzimidazoles

The 2‐nitrophenylhydrazones 2 of D‐arabino‐2‐hexulopyranosonic acid, D‐arabinose, D‐galactose and D‐galacturonic acid are used as precursors to form chiral functionalized 1,2,4‐benzotriazines and benzimidazoles by reductive cyclization methods. Catalytic hydrogenation provided the amine derivatives which are cyclized and air oxidized in alkaline solution to yield the novel 1,2,4‐benzotriazines 3 as the main products, while on acid catalysis the benzimidazoles 4 are formed.