A Novel Amphiphilic Chiral Ligand Derived from d-Glucosamine. Application to Palladium-Catalyzed Asymmetric Allylic Substitution Reaction in an Aqueous or an Organic Medium, Allowing for Catalyst Recycling

Abstract

A novel amphiphilic phosphinite−oxazoline chiral compound, 2-methyl-4,5-[4,6-O-benzylidene-3-O-bis{4-((diethylamino)methyl)phenyl}phosphino-1,2-dideoxy-α-d-glucopyranosyl]-[2,1-d]-2-oxazoline (1), has been prepared from natural d-glucosamine hydrochloride. The newly prepared complex, [Pd(2-methyl-4,5-[4,6-O-benzylidene-3-O-bis{(4-((diethylmethylammonium)methyl)phenyl)}phosphino-1,2-dideoxy-α-d-glucopyranosyl]-[2,1-d]-2-oxazoline)(η³-C₃H₅)]³⁺·3BF₄^- (3), is soluble in water and an efficient catalyst for asymmetric allylic substitution reaction in water or an aqueous/organic biphasic medium (up to 85% ee). This catalytic system offers an easy separation of the aqueous catalyst phase from the product phase and allows recycling of the catalyst phase. In addition, compound 1 also works as an effective ligand for the palladium-catalyzed reaction under conventional homogeneous conditions in an organic medium, in which the catalyst (Pd−1 complex) can be recovered by simple acid/base extraction and reused in the second reaction.