Two-Step Synthesis of 1,3-Oxazin-6-One Derivatives Involving <i>N-</i> Selective Alkenylation of Isoxazol-5-Ones Using β-Phenylsulfonylenone Alkenyl Donors

A highly regioselective <i>N</i>-alkenylation of isoxazol-5-ones using β-phenylsulfonylenones as alkenyl donors quickly afforded <i>N</i>-alkenylisoxazol-5-one derivatives in excellent yield. Subsequent treatment of these derivatives with 1,8-diazabicyclo(5.4.0)undec-7-ene (DBU) generated 1,3-oxazin-6-one derivatives in high yield. To our knowledge, this report is the first report to successfully synthesize 1,3-oxazin-5-one derivatives via <i>N</i>-selective alkenylation of isoxazol-5-one derivatives and subsequent transformation of the resulting <i>N</i>-alkenylisoxazol-5-ones.