Asymmetric Synthesis of Tetrahydroindolizines by Bimetallic Relay Catalyzed Cycloaddition of Pyridinium Ylides.

A highly enantioselective synthesis of tetrahydroindolizines by catalytic multicomponent cycloaddition reactions of diazoacetate, pyridine, and alkenyloxindole was developed. Under the relay catalysis, involving an achiral iron(III) catalyst and chiral N,N'-dioxide-scandium(III) complex, a series of tetrahydroindolizines bearing different substituents were obtained in moderate to high yields (up to 99 %) with excellent diastereo- and enantioselectivities (up to >19:1 d.r., 99 % ee).