Abstract
Mediated by chiral, non-racemic ligands, organolithiums add enantioselectively to C=O functions of carbonyl compounds (aldehydes and ketones) or cleave enantioselectively C-O units in strained ethers (epoxides and oxetanes) as well as in acetals. The achievement of high enantioselectivities is desirable and hence factors controlling these enantioselectivities are the subject of intensive research. Beneficial external influences on enantioselectivity are low temperatures, suitable solvents (e.g. dimethoxymethane, dimethyl ether) and the exclusion of salt impurities. Organolithium reagents and ligands lithiated in situ form mixed anionic aggregates, some of which can be isolated and even structurally studied. The improved understanding of the nature of such chiral organolithium aggregates provides the way to a more rational design of new enantioselective organolithium reagents.
1 Introduction
2 Additions to Aldehydes
3 Additions to Ketones
4 Additions to Epoxides and Oxetanes
5 Additions to Acetals
6 Conclusions
Key words
organolithiums - enantioselectivity - chiral ligands - carbonyl compounds - strained ethers - acetals