Formal [7+2] Cycloaddition of Arynes with N-Vinyl-α,β-Unsaturated Nitrones: Synthesis of Benzoxazonines and Their N-O Bond Cleavage

Various benzoxazonines were synthesized through a formal [7 + 2] cycloaddition of arynes with N-vinyl-alpha,beta-unsaturated nitrones under mild conditions. Controllable N-O bond cleavage of benzoxazonines afforded polysubstituted pyrrole-tethered benzopyrans and acyclic ketone-substituted phenols in moderate to good yields. Further transformations provided a facile approach to access useful building blocks with specific stereoselectivity.