Highly Efficient Synthesis of Polysubstituted 1,2-Dihydroquinolines via Tandem Reaction of α-Ketoesters and Arylamines Catalyzed by Indium Triflate

A simple and efficient method for the synthesis of polysubstituted 1,2-dihydroquinolines has been developed via an indium(III) catalyzed tandem reaction of alpha-ketoesters with primary or secondary aromatic amines. With respect to the reactions of pyruvates with amines indium triflate (1 mol %) demonstrated superior catalytic activity and efficiency compared with previously AuCl(3)/AgSbF(6) (5 mol %/15 mol %) cocatalyst. The reactions of alpha-alkyl substituted ketoesters and arylamines, which could not be effectively accomplished by the previous AuCl(3)/AgSbF(6) and HNO(3) catalytic systems smoothly in the presence of 10 mol % In(OTf)(3) to afford the desired products in moderate to good yields (43%-91%).