“Green” Asymmetric Synthesis: The Catalysts

Abstract

The structural optimization of catalysts is a key topic in the development of more sustainable asymmetric catalysis. An astonishing variety of chiral ligands for transition-metal complexation is today available and the identification of novel active compounds has been aided by computational and mechanistic studies as well as combinatorial methodologies. Besides the most investigated C 2 -symmetrical ligands, the potentiality of unsymmetrically disubstituted or monodentate ligands has been explored in conjunction with less toxic and/or less expensive metals whereas chiral amplification and enantiomer-selective effects resulted in the option to use non-enantiopure ligands saving satisfactory enantioselectivity. In the last years different classes of simple organic molecules have been shown highly effective in promoting a range of catalytic enantioselective transformations of carbonyl and iminic substrates through a number of general activation modes and organocatalysis has been recognised as a powerful methodology complementary to metal-based asymmetric synthesis. More recently, the concept of dual activation has led to the development of bifunctional catalysts with excellent performances.