High Diastereoselectivity in the Conjugate Addition of Functionalized Alcohols to a Chiral(E)-Nitroalkene

Modest to high diastereoselectivites have been observed in the conjugate addition of functionalized alcohols to chiral (E)-nitroalkene 1 depending on the presence of metal catalysts at low tempertwre. The resultS indicated that the anti-form had been preferred in all cases.

Orbital Phase Theory and the Diastereoselectivity of Some Organic Reactions

The orbital phase refers to the relationship between orbitals that originates from their wave character. We show here that the orbital phase essentially determines the diastereoselectivity of the following three organic reactions. 1) Torquoselectivity of the electrocyclicring-opening reaction of 3-substituted cyclobutenes;2) Contradictory torquoselectivity of the retro-Nazarov reaction;3) Diastereoselectivity in electrophilic addition to substituted ethylenes.

DIASTEREOSELECTIVITY OF ALLYBORATION OF ALDEHYDES

Reaction of(Z)-Crotyldiisopinocampheylborane with a series of alde- hydes have been examined,and the ratio of erythro to threo products varies fr- om 20:1 to 1:1.The results are discussed in detail.

Mechanism and origin of diastereoselectivity of N-heterocyclic carbene-catalyzed cross-benzoin reaction:A DFT study

Herein,the origin of the diastereoselectivity of N-heterocyclic carbene(NHC)-catalyzed cross-benzoin reactions between an a-amino aldehyde and furfural was studied by density functional theory.The computational results showed that the reaction proceeded through four steps:nucleophilic addition of NHC onto furfural,formation of a Breslow intermediate,cross-coupling reaction between Breslow intermediate and a-amino alde hyde,and dissociation of the catalyst.The cross-coupling was identified as the diaste reoselectivity-determining step,with the R-configured product generated preferentially.Noncovalent inte raction(NCI)analysis showed that the C-H…O and C-H…F inte ractions were responsible for determining the diastereoselectivity.

Enantioselective Conjugate Addition-Protonation of 5H-Oxazol-4-ones and 5-Methylene 1,3-Oxazolidine-2,4-diones: 2,2'-Biphenol-lnduced Diastereoselectivity Switch

A synthetic strategy for catalytic asymmetric conjugate addition-protonation and diastereoselective switch between 5H-oxazol-4-ones and 5-methylene 1,3-oxazolidine-2,4-diones was established.An array of chiral conjugate addition-protonation products bearing 1,3-O-heterotertiary-O-heteroquarternary nonadjacent stereocenters were obtained in excellent yields,moderate to good diastereoselectivities,and excellent enantioselectivities (up to 97% yield,11:1 dr,and 98% ee).Induction by 2,2'-biphenol could effectively promote the production of the corresponding diastereoisomers via cycloaddition intermedia.

An Efficient System TiCl_4-Al for the Homocoupling Reaction of Aromatic Aldehydes

The reduction of TiCl4(THF)2 with Al in CH2Cl2 gave a green solution of [Ti2(μ-Cl)2Cl4· (THF)4] (1) which was found to promote the reductive homocoupling of aromatic aldehydes to yield symmetrical 1, 2-diols with high diasterepselectivities.

Enantioselective Aldol Reactions of Aliphatic Aldehydes with Singh’s Catalyst

Aldols from aliphatic aldehydes had been synthesized enantioselectively using Singh’s catalyst. Self and crossed aldol reactions with several linear aldehydes were performed.

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.

Asymmetric Synthesis of Fluorinated Vicinal Diamines from Fluoromethyl Sulfinyl Imines and Diphenylmethylene-Benzylamines

A novel strategy was developed for the asymmetric synthesis of fluorinated vicinal diamines.Deprotonation of N-(diphenylmethylene)-benzylamines under base,followed by asymmetric nucleophilic addition to N-tert-butanesulfinylfluoroacetaldimines,a pair of diastereomeric isomers were afforded.The diastereomeric isomers can be easily separated from each other by silica gel column chromatography.The absolute steric configuration of two isomers was confirmed by single crystal X-ray diffraction analyses.The proposed mechanism revealed that the configuration of the carbon next to tert-butanesulfinyl was well controlled to be R by the chiral auxiliary.

Asymmetric Baylis-Hillman Reaction between Chiral Activated Alkenes and Aromatic Aldehydes in Me_(3)N/H_(2)O/Solvent Medium

Chiral activated alkene, L-menthyl acrylate and （＋）-N-α-phenylethyl acrylamide, induced asymmetric Baylis-HiUman reaction of aromatic aldehydes was realized at 25℃ for 7 days in Me3N/H2O/solvent homogeneous medium. The corresponding Baylis-Hillman adducts were obtained in good chemical yield with moderate to excellent diastereoselectivity （up to 99% de）.

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 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.

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.

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.

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%.

Modular Synthesis of Multi-substituted Cyclobutanones Enabled by Oxyallyl Cations

Stereoselective synthesis of multi-substituted cyclobutanes with different substituents is still a daunting challenge in organic synthesis.We report here a practical and facile approach to synthesizing all-trans 2,3,4-trisubstituted cyclobutanones from readily available dichlorocyclobutanones.The substitution reaction proceeds smoothly via oxyallyl cation intermediates under mild basic conditions.Further transformation to the synthesis of 1,2,3,4-tetrasubstituted cyclobutanes was also explored.