Conventional and non-conventional catalytic systems for the asymmetric reduction of cyclic imines

The asymmetric reduction of cyclic imines, such as dihydroquinolines and isoquinolines is still an unmet goal. In this regard, AH and ATH reduction of these compounds were evaluated using Ir(I) cyclooctadiene complex bearing a chiral atropoisomeric diphoshine in presence of H2 and [Ir(III)Cp*L2] as catalyst in which L2 is instead a rigid chiral diamine respectively. The so-called hybrid catalysts, derived from the combination of transition metal catalysts and enzymes properties represent a new type of catalytic approach, developed in the last decade. Two different artificial imine reductases were set up. The first one relied on a chiral biotinylated 1,3 diamine ligand in coordination with an iridium(III) center and anchored to different streptavidin mutants whereas in the other one the biotin anchor is introduced at the Cp* moiety in a series of Ir(III)/chiral diamine complexes. An innovative alternative to the classical biotin/(strept)avidin second sphere coordination system and to artificial metallo-enzymes could be the dalbapeptides/D-Ala-D-Ala dimer interaction system. The so obtained hybrid catalysts have been employed in the stereoselective reduction of the salsolidine precursor under ATH reaction conditions. Preliminary data will be presented.