Abstract
Starting from the chiral 5,6,7,8-tetrahydroquinolin-8-ol core, a series of amino-phosphorus-based ligands was realized. The so-obtained amino-phosphine ligand (L1), amino-phosphinite (L2) and amino-phosphite (L3) were evaluated in iridium complexes together with the heterobiaryl diphosphines tetraMe-BITIOP (L4), Diophep (L5) and L6 and L7 ligands, characterized by mixed chirality. Their catalytic performance in the asymmetric hydrogenation (AH) of the model substrate 6,7-dimethoxy-1-phenyl-3,4-dihydroisoquinoline 1a led us to identify Ir-L4 and Ir-L5 catalysts as the most effective. The application of these catalytic systems to a library of differently substituted 1-aryl-3,4-dihydroisoquinolines afforded the corresponding products with variable enantioselective levels. The 4-nitrophenyl derivative 3b was obtained in a complete conversion and with an excellent 94% e.e. using Ir-L4, and a good 76% e.e. was achieved in the reduction of 2-nitrophenyl derivative 6a using Ir-L5.
Highlights
Many pharmaceutically active compounds owe their physiological activity to the presence of an aminic group in their structure
It is well known that the steric hindrance of the ligands plays an important sources of chirality in organometallic catalysts for asymmetric reduction or for C–B bond formation role in the asymmetric reduction of this substrate, and matching the hindrance of both catalyst and reactions [38,39,40], we decided to focus our attention on the synthesis of three amino monophosphine substrate could enhance the performance of the asymmetric reduction
Different types of chiral phosphines serving as a source of chirality in an atropoisomeric moiety due to the presence of axial biaryl asymmetry were evaluated in the reduction of a standard cyclic imine, 6,7-dimethoxy-1-phenyl-3,4-dihydroisoquinoline 1a
Summary
Many pharmaceutically active compounds owe their physiological activity to the presence of an aminic group in their structure. 1,2,3,4–tetrahydroquinolines and their analogs are very important building blocks for the synthesis of biologically active compounds [1,2,3] such as salsolidine [4,5,6,7] and carnegine [8], solifenacin [9], cryptostyline [10], complex alkaloids [11,12,13,14] and new derivatives active as anti-HIV agents [15] and as anticonvulsants (as an inhibitor of carbonic anhydrase [16] or as a non-competitive antagonist via interaction with the glutamate ionotropic AMPA receptor complex) [17] (Figure 1). It is well known that the steric hindrance of the ligands plays an important role in the Catalysts 2020, 10, 914; doi:10.3390/catal10080914 www.mdpi.com/journal/catalysts
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