Synthesis of 1,4-benzoxazines via Y(OTf) 3 -catalyzed ring opening/annulation cascade reaction of benzoxazoles with propargylic alcohols.

A convenient Y(OTf) 3 -catalyzed cascade formal [4 + 2] cyclization approach for the formation of 1,4-benzoxazine scaffolds from benzoxazoles and propargyl alcohols through a ring-opening and regioselective ring-closure process has been developed. By using this mild and practical protocol, a broad range of aldehyde-containing 1,4-benzoxazine compounds were prepared in moderate to excellent yields with good functional group tolerance. Mechanistic studies indicated that an S N 1 nucleophilic substitution of benzoxazole with a propargyl cation was involved in this transformation.