Copper-Catalyzed Asymmetric Propargylic [3 + 2] Cycloaddition: Synthesis of Enantioenriched Dihydrofuro[3,2-]coumarins and its Quinolinone and Thiocoumarin Analogues.

A copper(II)-P,N,N-ligand catalyzed propargylic [3 + 2] cycloaddition approach for the synthesis of optically enriched dihydrofuro[3,2-]coumarins has been accomplished for the first time. The cycloaddition utilizes propargylic esters as C2-bis-electrophiles and 4-hydroxycoumarin derivatives as C,O-bis-nucleophiles. In addition, this novel strategy was also explored with 4-hydroxy-2-quinolinones and 4-hydroxythiocoumarins. Moreover, various dihydrofuro[3,2-]coumarins and their quinolinone and thiocoumarin analogues were synthesized in moderate to good yields with high enantioselectivities.