Chuchi Tang

Highly enantio- and diastereoselective Michael addition of cyclohexanone to nitroolefins catalyzed by a chiral glucose-based bifunctional secondary amine-thiourea catalyst

A novel bifunctional thiourea bearing a saccharide-scaffold and a secondary amino group was synthesized, and was proven to be an effective organocatalyst for the asymmetric Michael reaction of cyclohexanone to both aryl and alkyl nitroolefins. The corresponding adducts were obtained with excellent diastereo- (up to >99/1 dr) and enantioselectivities (up to 97% ee).

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%.

Organocatalyzed Enantioselective Michael Addition of 2-Hydroxy-1,4-naphthoquinone to β,γ-Unsaturated α-Ketophosphonatesθ

By employing a cinchonine-based thiourea as catalyst, highly enantioselective Michael addition reactions of 2-hydroxy-1,4-naphthoquinone to β,γ-unsaturated α-ketophosphonates were realized. The reaction afforded the corresponding β-substituted carboxylates in excellent yields with high levels of enantioselectivities (94->99% ee) upon quenching the generated parent structures with DBU and MeOH as a second nucleophile.

Enantioselective organocatalytic domino Michael/aldol reactions: an efficient procedure for the stereocontrolled construction of 2H-thiopyrano[2,3-b]quinoline scaffolds.

An efficient procedure for the stereocontrolled construction of 2H-thiopyrano[2,3-b]quinoline scaffolds has been developed, starting from simple compounds. The domino Michael/aldol reactions between 2-mercaptobenzaldehydes and enals, promoted by chiral diphenylprolinol TMS ether, proceed with excellent chemo- and enantioselectivity to give the corresponding synthetically useful and pharmaceutically valuable 2H-thiopyrano[2,3-b]quinolines in high yields with 90-99 % ee.

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.

Stereoselective Synthesis of Highly Functionalized Nitrocyclopropanes through the Organocatalyic Michael‐Addition‐Initiated Cyclization of Bromonitromethane and β,γ‐Unsaturated α‐Ketoesters

A highly diastereo- and enantioselective cyclopropanation of β,γ-unsaturated α-ketoesters with bromonitromethane has been successfully developed through a domino Michael-addition/intramolecular-alkylation strategy. Acceptable yields (up to 89%) and enantioselectivities (up to 96% ee) have been obtained.

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%.