Synthesis of the bifunctional BINOL ligands and their applications in the asymmetric additions to carbonyl compounds

Abstract

Efficient one-step syntheses of the bifunctional BINOL and H 8BINOL ligands ( S)- 6 and ( S)- 8 have been developed from the reaction of BINOL and H 8BINOL with morpholinomethanol, respectively. The X-ray analyses of these compounds have revealed their structural similarity and difference. The bifunctional H 8BINOL ( S)- 8 is found to be highly enantioselective for the reaction of diphenylzinc with many aliphatic and aromatic aldehydes and especially is the most enantioselective catalyst for linear aliphatic aldehydes. Unlike other catalysts developed for the diphenylzinc addition which often require the addition of a significant amount of diethylzinc with cooling (or heating) the reaction mixture in order to achieve high enantioselectivity, using ( S)- 8 needs no additive and gives excellent results at room temperature. ( S)- 8 in combination with diethylzinc and Ti(O i Pr) 4 can catalyze the highly enantioselective phenylacetylene addition to aromatic aldehydes. It can also promote the phenylacetylene addition to acetophenone at room temperature though the enantioselectivity is not very high yet. Without using Ti(O i Pr) 4 and a Lewis base additive, ( S)- 8 in combination with diethylzinc can catalyze the reaction of methyl propiolate with an aldehyde to form the highly functional γ-hydroxy-α,β-acetylenic esters except that the enantioselectivity is low at this stage. The bifunctional BINOL ligand ( S)- 6 in combination with Me 2AlCl is found to be a highly enantioselective catalyst for the addition of TMSCN to both aromatic and aliphatic aldehydes.