Diastereoselective α-Alkylation of β-Amino Esters: Preparation of Novel α-Substituted β-Amino Esters from α-Amino Acids

Enantiomerically pure a-substituted bamino esters were prepared from natural L-a-amino acids through Arndt-Eistert homologation and diastereoselective aalkylation.

Diastereoselective Syntheses of (+)-α-Cyperone and Its C-10 Epimer

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Diastereoselective Catalytic Hydrogenation of Schiff Bases of <i>N</i>-Pyruvoyl-(<i>S</i>)-Proline Esters

Diastereoselective catalytic hydrogenation of pyruvic acid esters, amides, and their Schiff bases has been well studied over a long period to show that proline is one of the most effective chiral auxiliaries. Proline derivatives have been used as auxiliaries in the diastereoselective catalytic hydrogenation of pyruvamide Schiff bases. The diastereoselective hydrogenation resulted in up to a 78% enantiomeric excess of the amino acid derived from the hydrolysis of the dipeptide products. The chelation hypothesis explains the stereochemistry of the catalytic hydrogenation using (S)-proline esters in the amide moiety and the two chiral centers in the amide and Schiff base moieties.

Studies on the Diastereoselective Alkylation Reaction Employing Isomannide and Isosorbide as Chiral Auxiliaries

The studies on the asymmetric alkylation of ester employing D-Isomannide and D-isosorbide as chiral auxiliaries were described. The diastereomeric excess of this reaction was up to 90%.

Studies on Diastereoselective Intramolecular meta-Cycloaddition of Arene to Olefin (Part Ⅱ)

The photoinduced intramolecular meta-cycloaddition of bichromophores 1a-1d gave diastereoselectively two types of adducts 2a-2d and 3a-3d respectively. The observed stereochemistry of cycloaddition is rationalized in terms of hydrogen bond effect induced by the 4hydroxy group in the 5-phenylpent-1-ene skeleton.

Gold-catalyzed addition reaction between creatinine and isatin:A sustainable and green chemistry approach for the diastereoselective synthesis of 3-substituted-3-hydroxyisatins

The aldolization of various isatins with creatinine under gold catalysis in water has been developed.The reaction is operationally simple as the products can be isolated by simple filtration without requiring tedious solvent extraction and column chromatographic techniques.The generality of this methodology is showcased through the reactions of a wide range of isatin derivatives with creatinine to afford the respective aldol products in excellent yields with complete syn‐selectivity.The scope of this chemistry is further extended to a tandem reaction involving isatins,creatinine and malononitrile to afford multicomponent products in excellent yields with complete anti‐selectivity.The antioxidant potency of the synthesized compound was assessed by a spectrophotometric method,which revealed that three compounds containing halogen atoms(2c,2d and2e)were the most active compared with the standard.

Studies on Diastereoselective Intramolecular meta-Cycloaddition ofArene to Olefin (Part I)

The photoinduced intramolecular meta-cycloaddition of bichromophores 1a-1d gave diastereoselectively two types of adducts, 2a-2d and 3a-3d. respectively. The observed stereochemistry of cycloaddition was rationalized in terms of hydrogen bond effect induced by the 3-hydroxy group in the 5-phenylpent-1-ene skeleton.

A Highly Diastereoselective Three-component Domino Reac- tion in Water Yielding Poly-substituted 4,5-Dihydropyrroles

An efficient methodology for highly diastereoselective synthesis ofpoly-substituted 4,5-dihydropyrrole deriva- tives from readily available common reactants in water has been developed. During domino processes, the forma- tion of pyrrole skeleton and its C2-hydroxylation and C3-arylamination were readily achieved via metal-free [3 ＋2] heterocyclization in a one-pot operation.

Total syntheses of hyperaspidinols A and B enabled by a bioinspired diastereoselective cascade sequence

A bioinspired acid-triggered hemiacetalization/dehydration/[3 + 3]-type cycloaddition cascade process was disclosed, diastereoselectively furnishing furo[2,3-b]chromene skeleton under mild conditions. The viability of this approach was demonstrated by syntheses of a series of furo[2,3-b]chromene and pyrano[2,3-b]chromene derivatives. The successful total syntheses of two lignan-phloroglucinol hybrids,hyperaspidinols A and B, exemplified the synthetic utility of our biomimetic methodology.

Diastereoselective 2,3-diazidation of indoles via copper(Ⅱ)-catalyzed dearomatization

The copper-catalyzed directed dearomatization of indoles with the assistance of directing groups has been developed for the synthesis of 2,3-diazido indolines with good yields and excellent diastereoselectivities in aqueous solution.The resultant 2,3-diazides can be smoothly converted to other functional groups,including vicinal diamines,triazoles and benzotriazoles,in a single step.

Diastereoselective Synthesis of Chiral Pyrrolidine and Piperidine Ring Systems

A diastereoselective method for the synthesis of chiral pyrrolidine and piperidine ring containing compounds was described. The protocol of bromination followed by aminocyclization furnishes an easily handled while highly efficient procedure for the intramolecular amidation of an isolated double bond. High diastereomeric excess was observed in this synthetic procedure.

Diastereoselective alkylation of the (+)-ketopinic acid ketimine derived from benzylamine

Alkylation of the ketimine 2 obtained from condensation of (+)-ketopinic acid and benzyla- mine with a variety of alkylating agents gives the products whose trends in diastereomeric excesses (1- 100% O. P.) appear to correlate with the structure and reactivity of electrophilic agents. Using excess n-butyl lithium and allylic or benzylic halides, β-alkylation occured.

An efficient Bi/NH_4I-mediated addition reaction for the highly diastereoselective synthesis of homoallylic alcohols in aqueous media

An efficient water-based bismuth-mediated addition reaction of carbonyl compound with cyclic allylic halide was developed.The reactions proceeded smoothly in aqueous DMF in the presence of ammonium iodide to afford the corresponding syn-homoallylic alcohols in moderate to good yields with excellent diastereoselectivities(>99:1 syn:anti).Reversal of product diastereoselectivity was observed when heteroaryl aldehyde possessing an adjacent chelating nitrogen atom was employed as substrate.

1,8-Diazabicyclo[5.4.0]undec-7-ene （DBU） Catalyzed Regio specific and Diastereoselective Reaction of Chiral N-（tert-Butanesulfinyl）ketimines and α,β-Unsaturated Trifluoromethyl Ketones

The reaction of chiral N-（tert-butanesulfinyl）ketimines and α,β-unsaturated trifluorotuethyl ketones catalyzed by DBU was achieved under mild conditions. 1,2-Addition products, precursors of chiral trifluoromethylated 1,3-amino alcohols, were obtained diastereoselectively （dr value up to 95 ： 5） in moderate yields （up to 76%）. A possible catalytic cycle was proposed.

Diastereoselective Photoreaction of Ir(III) Amine Complexes for Generation of New Multidentate Ligands in situ via a Postcoordinated Interligand-Coupling Strategy

The diastereoselective photoreactions of Ir(III)-amine and Ir(III)-diamine complexes are observed in the presence of O2.TheɅ-[Ir(pq)_(2)(R-mapy)](PF_(6))(pq is 2-phenylquinoline and mapy is 2-(1-aminoethyl)pyridine)diastereomer is dehydrogenatively oxidized into imine complexɅ-[Ir(pq)_(2)(mapy-2H)](PF_(6))at room temperature,while theɅ-[Ir(pq)_(2)(S-mapy)](PF_(6))diastereomer occurs interligand C—N cross-coupling reaction at 60℃,affording a new tetradentate complexɅ-[Ir(pq)(S-pqpe)](PF_(6))(pqpe is 2-phenyl-N-(1-pyridin-2-yl)ethyl-quinolin-8-amine).The identical cases are also observed in diamine complexesɅ-[Ir(pq)_(2)(R,R-chda)](PF_(6))(chda is 1,2-diaminocyclohexane),Ʌ-[Ir(pq)_(2)(R,S-chda)](PF_(6)),andɅ-[Ir(pq)_(2)(S,S-chda)](PF_(6)),where the R configuration ligand is dehydrogenatively oxidized into imine,while the S configuration is retentive and the bound nitrogen atom is coupling to the C8 of pq ligand,affordingɅ-[Ir(pq)_(2)(chdi)](PF_(6))(chdi is 1,2-diiminocyclohexane),Ʌ-[Ir(pq)(S-pqchim)](PF_(6))(pqchim is N-(2-iminocyclohexyl)-2-phenyl-quinolin-8-amine),andɅ-[Ir(S,S-pqchda)](PF_(6))(pqchda is N',N”-bis(2-phenylquinolin-8-yl)cyclohexane-1,2-diamine),respectively.These provide a new and useful protocol for the synthesis of multidentate ligands in situ via the postcoordinated interligand-coupling strategy under mild conditions.

HFIP-catalyzed highly diastereoselective formal[4+2]cyclization to synthesize difluorinated multisubstituted chromans using difluoroenoxysilanes as C2 synthons

A hexafluoroisopropanol(HFIP)-catalyzed highly diastereoselective formal[4+2]cyclization between ortho-hydroxyphenyl para-quinone methides and difluoroenoxysilanes is developed.This tandem protocol provides a simple and straightforward approach to assemble diverse multiply functionalized difluorinated chromans with high to excellent diastereoselectivity by employing difluoroenoxysilane as a new C2 synthon.

Diastereoselective Synthesis of 1,10-Dihydropyrrolo [ 1,2-a] [1,10]phenanthroline Derivatives via 1,3-Dipolar Cycloaddition Reaction

The functionalized 1,10-dihydropyrrolo[1,2-a][1,10]phenanthroline derivatives were synthesized in good yields and with high diastereoselectivity by 1,3-dipolar cycloaddition reactions of N-phenacylphenanthrolinium bromides or N-ethoxycarbonylmethylene phenanthrolinium bromide with various nitrostyrenes in acetonitrile at room temperature in the presence of triethvlamine,

Diastereoselective synthesis of functionalized tetrahydro-γ-carbolines via a[3+3] cycloaddition of 2,2’-diester aziridines with β-(indol-2-yl)-α,β-unsaturated ketones

A Sc(OTf)3-catalyzed[3+3]cycloaddition of 2,2’-diester aziridines withβ-(indol-2-yl)-α,β-unsaturated ketones was developed,affording polysubstituted tetrahydro-y-carbolines in single diastereoisomers in good to excellent yields.

Synthesis and Structural Determination of (2R,4S,SS)-(+)-Threo-5-(2,2-dichloroacetamido)-4-(4-nitrophenyl)-2-aryl-1,3-dioxanes

(2R,4S,SS)-(+)-threo-5-(2,2-dicloroacetamido)-4-(4-nitrophenyl-2aryl-l,3dioxanes, were synthesized with high diastereoselectivity and good yields. The structuresofacetals were determined and the configurations were confirmed by 2D-NMR (NOESY).

Synthetic Studies of Didemnaketals Analogue-Construction of the Intermediate (3S,5S,6R)-3,7-Dimethyl-5,6,7-trihydroxy-octanal

An efficient and stereoselective synthetic procedure for (3S,5S,6R)-3,7-dimethyl-5,6,7-trihydroxy-octanal derivative, the intermediate for synthetic of the HIV-active didemnaketals analogue. was developed via a series of reactions from the natural (+)-Pulegone. In this approach, an efficient diastereoselective reaction of the epoxides 8 and 9 with PCC has been accomplished.