New chiral monophosphite ligands containing BINOL and/or H8-BINOL bearing adamantyl substituents: effect of ligand scaffold on the enantioselective 1,4-conjugate addition of diethylzinc to cyclic enones

摘要

A series of new bulky monophosphite ligands were synthesized from axially chiral BINOL/H8-BINOL (BINOL: 1-(2-hydroxynaphthalen-1-yl)naphthalen-2-ol) and highly sterically hindered adamantylcarbonyl chloride. The effectiveness of these ligands was evaluated by the Cu-catalyzed asymmetric 1,4-conjugate addition of diethylzinc to cyclic enones with enantioselectivities of up to 79% ee. The results showed that a ligand structure comprising a partially hydrogenated 2,2'-(1,1'-binaphthyl)phosphite scaffold and an adamantyl moiety was effective in improving the enantioselectivity.