Enantioselective Synthesis of Tetrahydroquinolines from 2-Aminochalcones via a Consecutive One-Pot Reaction Catalyzed by Chiral Phosphoric Acid

A new asymmetric protocol for the synthesis of chiral tetrahydroquinolines from 2-aminochalcones via a two-step one-pot consecutive process (cyclization/asymmetric reduction) has been developed using chiral phosphoric acid as the sole catalyst. 2-Aminochalcones were converted into the corresponding quinolines through chiral phosphoric acid-catalyzed dehydrative cyclization, and the resultant quinolines were subsequently reduced to the chiral tetrahydroquinolines via chiral phosphoric acid-catalyzed asymmetric reduction with Hantzsch ester. Various 2-aminochalcones could be applicable to this protocol, and the desired tetrahydroquinolines were obtained in excellent yields and with excellent enantioselectivities. Furthermore, the utility of this protocol has been successfully demonstrated in the highly efficient synthesis of estrogen receptor modulator.