Guo-Jun Deng

Preparation and use of MeO-PEG-supported chiral diphosphine ligands: soluble polymer-supported catalysts for asymmetric hydrogenation

Abstract Two new chiral MeO-PEG-supported ( R )-BINAP and (3 R ,4 R )-Pyrphos ligands were synthesized and employed in the Ru(II)- and Rh(I)-catalyzed asymmetric hydrogenation of 2-(6′-methoxy-2′-naphthyl)propenoic acid 5 and prochiral enamides 10 . The results showed that these new soluble polymeric catalysts exhibited high catalytic activity and enantioselectivity. Enantiomeric excesses (e.e.s) in the ranges 90–96% and 86–96% were achieved in the hydrogenation of 5 and 10 , respectively. Furthermore, these catalysts could be recovered easily and the recycled catalysts were shown to maintain their efficiency in subsequent reactions.

The synthesis of dendritic BINOL ligands and their applications in the enantioselective Lewis acid catalyzed addition of diethylzinc to aldehydes

Abstract Novel dendritic chiral BINOL ligands have been synthesized through coupling of MOM-protected 3,3′-dihydroxymethyl-binaphthol with Frechet-type polyether benzyl bromide dendrons followed by deprotection of the MOM groups using TsOH. These dendritic chiral BINOL ligands were found to be effective in the enantioselective addition of diethylzinc to benzaldehyde both in the presence and absence of Ti(O-iso-Pr)4. The enantioselectivity decreased with increasing generation in both cases. In the latter case, the dendritic chiral BINOL ligands showed much higher catalytic activity and enantioselectivity than BINOL.

Dendritic BINAP based system for asymmetric hydrogenation of simple aryl ketones

Abstract A series of dendritic BINAP-Ru/chiral diamine catalysts were developed for asymmetric hydrogenation of various simple aryl ketones. The resulting catalytic system showed very attractive due to very good catalytic activity and enantioselectivity as well as facile catalyst recycling. In the case of 1-acetonaphthone and 2′-methyl-acetophenone, interesting e.e. value up to 95% was observed which are comparable to the enantioselectivity reported by Noyori under similar conditions and higher than that of the heterogeneous poly(BINAP)-Ru catalyst reported by Pu and co-workers [Tetrahedron Lett. 41 (2000) 1681].

A highly effective water-soluble polymer-supported catalyst for the two-phase asymmetric hydrogenation: preparation and use of a PEG-bound BINAP ligand

Abstract A new type of amphiphilic PEG-bound BINAP ligand was synthesized through polycondensation of 5,5′-diamino BINAP ( 1 ), polyethylene glycol and terephthalyol chloride in the presence of pyridine. It was proven that ruthenium complex based on the new polymeric ligand was an effective catalyst for the asymmetric hydrogenation of prochiral α,β-unsaturated carboxylic acids in both ethyl acetate/water two-phase and in methanolic solvent systems. The activity and/or enantioselectivity in two-phase systems were observed to be higher than that in ethyl acetate or methanol–water homogeneous systems. The replacement of water with ethylene glycol increased the activity and enantioselectivity. The activity of the new catalyst was shown to be about 30 times higher in the two-phase hydrogenation of 2-(6′-methoxy-2′-naphthyl)-acrylic acid than the Ru(BINAP-4SO 3 Na) catalyst without the long hydrophilic polymer chain, which illustrated the importance of the amphiphilic structure of the polymeric ligand.

Chiral dendritic bis(oxazoline) copper(II) complexes as Lewis acid catalysts for enantioselective aldol reactions in aqueous media

Abstract A series of copper(II) complexes, with chiral bis(oxazoline) ligands disubstituted at the carbon atom linking the two oxazolines by Frechet-type polyether dendrimers, have been designed and synthesized. These complexes were used as Lewis acid catalysts in enantioselective aldol reactions in aqueous media. Good yields and moderate enantioselectivities were achieved, which are comparable with those resulting from the corresponding smaller catalysts.

New soluble bifunctional polymeric chiral ligands for enantioselectively catalytic reactions

Abstract Two new soluble bifunctional polymeric ligands ( R , R )- 4 and ( R , R )- 5 have been prepared via the direct condensation reaction of ( R )-3,3′-diformyl-1,1′-bi-2-naphthol ( R )- 1 with ( R )-5,5′-diamino BINAP ( R )- 2 and with ( R )-5,5′-diamino BINAPO ( R )- 3 , respectively. The different types of catalytic centers, BINOL and BINAP or BINAPO, were alternatively organized in a regular chiral polymer chain. Both polymeric ligands were found to be effective in the addition of diethylzinc to benzaldehyde either in the presence or in the absence of Ti(OPr i ) 4 with different enantioselectivities. ( R , R )- 4 /Ti(IV) catalyst, which showed similar efficiency to the parent catalyst BINOL/Ti(IV), was more enantioselective than ( R , R )- 5 /Ti(IV). ( R , R )- 4 was also found to be highly effective in the Ru(II)-catalyzed asymmetric hydrogenation of 2-arylacrylic acids. The results demonstrated that the use of the co-polymer catalyst rather than a mixture of monomer catalysts not only simplified the recycling of the catalyst, but also improved the enantioselectivity and/or the activity in some cases.

Efficient pyrido[1,2-a]benzimidazole formation from 2-aminopyridines and cyclohexanones under metal-free conditions

An efficient procedure for pyrido[1,2-a]benzimidazole preparation from 2-aminopyridines and cyclohexanones under metal-free conditions is described. Non-aromatic cyclohexanones were used as the aryl source via a dehydrogenation–aromatization process using molecular oxygen as the green oxidant.

Transition-metal free 2-arylbenzoxazole formation from aryl amides and cyclohexanones

A transition-metal-free method for the synthesis of 2-arylbenzoxazoles from readily available cyclohexanones and benzamides is described. The combined use of KI, p-TsOH and DMSO significantly improved the reaction yields. Non-aromatic cyclohexanones were smoothly dehydrogenated and acted as the aryl source using oxygen as the oxidant.

Iodine-promoted 2-arylsulfanylphenol formation using cyclohexanones as phenol source

A novel method for the formation of 2-arylsulfanylphenols using cyclohexanones as phenol source via dehydrogenation is described. Various aromatic sodium sulfinates and sulfonyl chlorides acted as efficient coupling partners to construct new C–S bonds in the presence of an iodine promoter.

Three-component synthesis of 2-heteroaryl-benzothiazoles under metal-free conditions

A three-component procedure for the preparation of 2-heteroaryl-benzothiazoles from anilines, 2-methylquinolines and sulfur powder is described. This reaction was promoted using NH4I to give the corresponding biheteroaryl products in moderate to good yields in the absence of metals.