KBr/K₂S₂O₈-mediated dibromohydration of N-(2-alkynylaryl)acetamide

The regioselective dibromohydration of N-(2-alkynylaryl)acetamide with the participation of a neighbouring acetamino group is described here for the synthesis of N-(2-(2,2-dibromo-2-arylacetyl)aryl)acetamide. The dibromohydration proceeds under mild conditions and works well without metal catalysis. More importantly, by employing different neighbouring groups, switchable synthesis can be achieved. The entire process of the dibromohydration of N-(2-alkynylaryl)acetamide consists of KBr/K₂S₂O₈-based electrophilic 6-exo cyclization to form bromo-containing benzoxazine cation and the oxidative ring-opening of the resulting bromo-containing benzoxazine cation. Water serves as a reagent to be incorporated into the acetamino group.