Phosphine-Catalyzed [3+2] Cyclizations:Applications to the Enantioselective Synthesis of Cyclopentene-FusedChromanones and Dihydroquinolinones

Phosphine-promoted [3+2] cyclizations of allenic esters or phosphonates with coumarin derivatives were used to synthesize functionalized bicyclo[4.3.0]chroman-2-ones. Analogous bicyclo[4.3.0]quinolinones were similarly prepared by a two-step strategy involving a phosphine-catalyzed [3+2] cyclization of diethyl propadienylphosphonate and 3-(2-nitrophenyl)acrylate as the key step. Enantiomerically enriched compounds, with enantiomeric excesses in the range 70-86%, were obtained by using (S,S)-Ferro-PHANE as the chiral catalyst for the cyclization step.