3.25 Stoichiometric Auxiliary Ligands for Metals and Main Group Elements: Ligands for Zinc

Abstract

This chapter will present an overview of the most effective stoichiometric auxiliary ligands for organozinc-mediated transformations. When appropriate, alternative reactions requiring catalytic amounts of a chiral ligand will be mentioned; however, this will be brief as this subject is covered in another chapter. The following organic transformations will be discussed: the addition of diorganozinc reagents to carbonyl and imine derivatives; the Reformatsky reaction (zinc enolate) and the cyclopropanation of alkenes (zinc carbenoid). In the first two classes of reactions, the chiral ligand is typically bonded to the Lewis acidic zinc center to promote the alkyl group transfer from zinc to the electrophilic substrate. In the last class of reactions (cyclopropanation), the chiral ligand either generates a chiral zinc carbenoid or it directs the cyclopropanation reaction through complexation.