Synthesis of Chiral Bulky Monophosphite Ligands and Their Application in Cu-Catalyzed Asymmetric Conjugate Addition of Diethylzinc to Cyclic Enones

Abstract

A series of new bulky monophosphite ligands were synthesized from axially chiral BINOL and highly sterically hindered adamantanecarbonyl chloride. These ligands were applied to the Cu-catalyzed asymmetric 1,4-conjugate addition of diethylzinc to cyclic enones and were found to have moderate enantioselectivities (up to 61% ee). The stereochemically matched combination of (S)-BINOL in ligand (S)-(2-(adamantane-1-carboxylic acid)-1,1′-binapthalen-2′-yl)-((S)-1,1′-binaphthalen-2,2′-yl)phosphite induces a moderate enantioselectivity. The sense of enantioselectivity is mainly controlled by the configuration of the 2,2′-o, o-(1,1′-binaphthyl)-dioxo-phosphite moiety of the ligands.