Solvent-Controlled Pd-Catalyzed Dearomative Reactions of Allenyl Benzoxazinones and 4-Nitroisoxazoles: Divergent Synthesis of Functionalized Quinolines and Fused Tetrahydroquinolines

We report an efficient solvent-modulated Pd-catalyzed dearomatization reaction between allenyl benzoxazinones and 4-nitroisoxazoles. When carried out in Diox, the transformation follows a cascade intramolecular cyclization/intermolecular dearomative Michael addition sequence, producing functionalized quinolines in up to 85% yield with >20:1 dr. In dichloromethane, the reaction proceeds through a dearomative formal [4 + 2] annulation instead, readily furnishing fused tetrahydroquinoline products with up to 83% yield and dr of >20:1. This work also constitutes the first report of dearomative reactivity derived from alkylidene−π-allylpalladium dipoles.