Ambiphilic p-Quinone Methides and α-Imino Ketones: Ca(II)-Catalyzed, One-Pot, Three-Component Synthesis of Benzoxazines.

A one-pot, three-component cyclization of 2-hydroxy p-quinone methides and in situ-formed α-imino ketones is described at room temperature to synthesize N-substituted 3,4-dihydro-2H-1,3-benzoxazine using a Ca(II) catalyst. The reaction involves a cascade etherification followed by an intramolecular 1,6-conjugate aza-addition. The NMR spectroscopy of the products indicates that the products are obtained as rotamers. Simple operation, wide substrate scope, and gram-scale synthesis demonstrate the protocol's competence.