Rh(III)-Catalyzed [4 + 2] Annulation of 3-Aryl-5-isoxazolone with Maleimides or Maleic Ester.

The Rh(III)-catalyzed [4 + 2] annulation of 3-aryl-5-isoxazolones with maleimides or maleic ester has been developed, which gives synthetically important 3,4-dihydroisoquinoline derivatives in good to excellent yields. This facile protocol can tolerate a variety of functional groups, and CO2 was produced as the predominant byproduct. Notably, a C-C bond and a C-N bond were formed simultaneously. This protocol could be easily scaled up.