Palladium-catalyzed asymmetric intermolecular arylation of cyclic or acyclic alkenes using phosphinite-oxazoline ligands derived from D-glucosamine

Chiral phosphinite-oxazolines, 2-alkyl- or 2-aryl-4,5-(4,6-O-benzylidene-3-O -(diphenylphosphino)-1,2-di-deoxy-alpha-D-glucopyranosyl)-[2,1-d]-2-oxazolines 1a-f derived from D-glucosamine hydrochloride, are revealed to work as effective P,N-bidentate ligands in the palladium-catalyzed enantioselective arylation of 2,3-dihydrofuran to give 2-aryl-2,5-dihydrofuran selectively in high yield with up to 96% ee. The first asymmetric phenylation reaction of trans- and cis-crotyl alcohols as acyclic alkenes with iodobenzene is also carried out to afford 3-phenylbutanal in moderate chemical yield with up to 17% ee. The complex [PdCl2(1b)] is newly prepared and its structure is characterized by X-ray crystallography. Structures of the new complex [(p-MeO2CC6H4)PdI(1a)] (8) and its cationic complex [(p-MeO2CC6H4)Pd(1a)]+OTf- (9) are also elucidated on the basis of H-1-,C-13-,and P-31-NMR spectra, p-MeO2CC6H4 moiety on the palladium being located trans to the nitrogen of la. This cofiguration might be responsible for an enantiofacial discrimination of 2,3-dihydrofuran to produce (R) isomer predominantly. The stoichiometric reaction of [PhPd(1f)]+OTf- (11) with 2,3-dihydrofuran has provided the mechanistic aspect for the arylation using P,N-ligands, in which the base-promoted deprotonation at P-position leading to an alkene(2-aryl-2,5-dihydrofuran)-palladium(0) complex has been shown to be an important step for the selective formation of the product. (C) 2000 Elsevier Science S.A. All rights reserved.