Abstract

Enantioselective imine reduction of dihydro-β-carbolines (DHBCs) is a reliable and powerful tool to construct bioactive chiral tetrahydro-β-carbolines (THBCs). Here, we report an efficient enantioselective imine reduction employing in situ generated Fe-thiosquaramides (Fe-TSQs) 3a and 3b as asymmetric organometallic catalysts to produce chiral THBCs (2a-h). The catalyst 3a at 15 mol % was found to be suitable for the substrates with alkyl and aryl groups which afford corresponding chiral THBCs with excellent enantioselectivities (up to ee 99%).