DBU‐Promoted Synthesis of 1,3‐Benzoxazines from Geminal Dibromo Olefins: Applications to the Construction of o‐Amido Phenacyl Bromides

Abstract Herein we demonstrated an approach for the synthesis of 1,3‐benzoxazines through 1,8‐Diazabicyclo(5,4,0)undec‐7‐ene (DBU) promoted annulation of geminal dibromoolefins. The key features of this work include good reaction yield, high regioselectivity, mild reaction condition, metal‐free approach, and broad scope. Synthetic application for some of the products is extended to achieve α‐bromomethyl Ketones (Phenacyl bromides) via ring opening sequence using stoichiometric amount of water and DMSO as solvent. We also successfully demonstrated the applicability to gram scale synthesis and one‐pot strategy. This protocol serves as an alternative approach to the conventional reaction of α‐bromination of ketones.