Zhenghong Zhou

Synthesis of new chiral Schiff bases and their application in the asymmetric trimethylsilylcyanation of aromatic aldehydes

Abstract The new chiral Schiff base ligands 1a – 1c were synthesized from (1 R )-(+)-camphor and found to be efficient catalysts for the enantioselective silylcyanation of aromatic aldehydes. The corresponding aromatic cyanohydrins were obtained in good yields and with enantiomeric excesses (e.e.s) of up to 73%.

Asymmetric carbonyl reduction with borane catalyzed by chiral phosphinamides derived from l-amino acid

Abstract Two types of chiral phosphinamide catalysts 3a–d and 4a–c were prepared from l -phenylalanine and l -proline, respectively. Their applications in the asymmetric borane reduction of prochiral ketones were investigated. The chiral secondary alcohols were obtained with excellent chemical yields and moderate to high enantiomeric excesses.

Enantioselective reaction of secondary alcohols with phthalimide in the presence of a chiral tri-coordinate phosphorus reagent in Mitsunobu reaction

Abstract The enantioselective reaction of racemic secondary alcohols with phthalimide has been carried out in the presence of a chiral cyclic phosphoramidite (+)- 1 /DEAD under Mitsunobu reaction conditions. Phthalimide reacted preferentially with the (−)-enantiomer of the alcohol to give a substituted imide (+)- 2 , while the unreacted enantiomeric alcohol, (+)- 3 was obtained in enantiomerically enriched form. Compound (+)- 2 was further treated with hydrazine hydrate to form the product amine, (+)- 4 .

ASYMMETRIC TRIMETHYLSILYL-CYANATION OF ALDEHYDES CATALYZED BY CHIRAL SCHIFF BASE-Ti(OiPr)4 COMPLEX

A new chiral Schiff base 4 was synthesized, which was found to be efficient catalyst for the enantioselective silylcyanation of aldehydes. The enantioselectivities of 25.1–72.7% were obtained by using the chiral Schiff base-Ti(OiPr)4 complex.

Regio- and stereoselective ring-opening of epoxides using organic dithiophosphorus acids as nucleophiles

Abstract A practical method for the synthesis of β-hydroxymercaptans has been successfully developed through the ring-opening of epoxides with organic dithiophosphorus acids 1 . Highly regio- and stereoselective products, β-hydroxyalkyl dithiophosphates, which were transformed to the corresponding synthetically valuable β-hydroxymercaptans by further reduction, were obtained under mild reaction conditions without any catalyst or promoter. Highly enantioselective ring-opening reaction of cyclohexene epoxide with 1 was realized in the presence of a chiral (salen)Ti(IV) complex.

SYNTHESIS OF A NEW CHIRAL o-HYDROXYARYLDIAZAPHOSPHONO- DIAMIDE AS LIGAND CATALYSTS FOR ASYMMETRIC SILYLCYANATION OF AROMATIC ALDEHYDES

ABSTRACT A new chiral o-hydroxyaryldiazaphosphonodiamide 1 was synthesized from (−)-α-methylbenzylamine, it was found to be efficient ligand for the Ti(O-iPr)4 catalyzed asymmetric trimethylsilylcyanation of aldehydes. Corresponding aromatic cyanohydrins were obtained in good chemical yield and enantiomeric excesses (e.e.s) up to 90%.

NEW CHIRAL PHOSPHORUS CATALYSTS DERIVED FROM (S)-BINAPHTHOL FOR HIGHLY ENANTIOSELECTIVE REDUCTION OF ACETOPHENONE BY BORANE

Abstract New chiral (+)-2,2′-O,O-(1,1′-binaphthyl)-dioxo-N,N-diethylphospholidine 1 and its borane complex 3 were prepared from (S)-binaphthol and their use as catalysts in enantioselective borane reductions of prochiral acetophenone were investigated. Enantiomeric excesses of up to 98.5% have been obtained using 6 mol% of 1 at room temperature and using 6 mol% of 3 at 100°C.

Synthesis of Novel Optically Active Cyclic Phospholipid Conjugates of Tegafur and Uridine Starting From L-Serine

Abstract Starting from L-serine, cyclic phospholids 2,3 and 4 were synthesized and successfully separated in the form of pure diastereomer. Their configurations were discussed and assigned according to their NMR spectra data. The asymmetric induction effects were also observed in two phosphorylation cyclizations.

Asymmetric ring-opening of cyclohexene oxide with mercaptan (thiophenols) catalyzed by chiral schiff BASE/Ti(OPr-i)4 or (-)-(S)-BINAPHTHOL/Ti(OPr-i)4

New chiral Schiff base ligands 1-4 were synthesized starting from (+)-camphor and (+)-1-(4-nitrophenyl)-2-amino-1,3-propanediol, and their application in asymmetric ring-opening of cyclohexene oxide using mercaptan (thiophenols) as nucleophiles was investigated. The aymmetric ring-opening of cylohexene oxide catalyzed respectively by chiral Schiff bases 1-4 /Ti(OPr- i ) 4 and ( m )-(S)-1,1-binaphthalene-2,2-diol 5 /Ti(OPr- i ) 4 complex afforded the corresponding chiral g -hydroxysulfides 6-10 in lower to good yield with lower to moderate ee values. Moreover, the using of ( m )-(S)-1,1-binaphthalene-2,2-diol as ligand led to better chiral induction effect.

SYNTHESIS OF SEVERAL CHIRAL PHOSPHINAMIDES AND THEIR APPLICATION IN THE ASYMMETRIC BORANE REDUCTION OF PROCHIRAL KETONES

INTRODUCTION The enantioselective reduction of prochiral ketones is an important route for the synthesis of optically active secondary alcohols which were widely used in the preparation of bioact ive substances .The enantioselevtive borane reduction catalyzed by oxazaborolidine prepared from chiral amino alcohols is one of the most efficient method which give excellent ee values and often have wide substrate scope. Other catalysts such as chiral sulfur reagents 5,1 and chiral phosphorous reagents were also used in this reaction. In recent years, great progress was achieved using chiral phosphorous reagents as catalysts for the reduction of prochiral ketones. In this paper, we reported several chiral phosphinamides compounds I, II and III prepared f rom (S) (+) -Be t t i Base , (D)-lR,2R-(-)threo-l-(p-Nitrophenyl)-2-amino-3-tr iphenylmethoxypropanol-1 and L-Serine respectively. Their application as ligand catalysts in the asymmetr ic borane reduction of prochiral ketones were investigated. M A T E R I A L S AND M E T H O D S H N M R and 3 I P N M R were recorded in CDCI3 as solvent on an AC-P200 instrument using T M S as internal standard and 85% H3PO4 as external standard, respectively. Elemental analyses were done on an MF-3 automatic analyzer. Melting points were determined on an MP-500 melting point apparatus. Optical rotations were measured on a Perkin-Elmer241MC Polarimeter. All temperatures were uncorrected. Preparation of l -(a-N-diphenylphosphinylaminobenzyl)-2-naphthol I (Scheme 1) Scheme I ph,,..C-NH2 ph|11.C_NHPPh2 OH Ph2P(0)CI ̂ S^J^o* j l| J Et3N/CH2Cl2 (S)-(+)Betti Base I