Search results for "SELE"

ChemInform Abstract: Stereoselective Synthesis of 2-Substituted Pyrrolidines.

2000

Using O -pivaloyl protected D-galactopyranosylamine and D-arabinopyranosylamine, ( S ) or ( R ) configured α-substituted homoallylamines are synthesized with high diastereoselectivity by reaction of the corresponding aldimines with allyltributylstannane. Electrophile-induced endo -trig-cyclization of these N -glycosylhomoallylamines gave the 2-substituted pyrrolidines of high diastereomeric purity.

Enantioselective Organocatalysis of Strecker and Mannich Reactions Based on Carbohydrates.

2007

Efficient organocatalysts for enantioselective Strecker and Mannich reactions were constructed from glucosamine as a readily accessible chiral scaffold. A variety of aromatic aldimines were subjected to hydrocyanation with good to excellent yield (72–98 %) and, in part, high enantioselectivity (69–95 % ee). Influence of the catalyst architecture on the enantioselectivity obviously arises from restrictions imposed on the conformational flexibility of the monosaccharidic backbone. In the asymmetric Mannich reaction moderate yields (up to 76 %) and enantioselectivities (up to 58 % ee) have been achieved with the described catalyst.

Aziridination of Aromatic Aldimines Through Stabilized Ammonium Ylides: A Molecular Electron Density Theory Study

2019

Enantioselective addition of terminal alkynes to N-(diphenylphosphinoyl)imines catalyzed by Zn–BINOL complexes

2012

Abstract Chiral nonracemic N-(diphenylphosphinoyl)-protected propargylic amines have been prepared by addition of terminal alkynes to N-(diphenylphosphinoyl)aldimines in the presence of dimethylzinc and 3,3′-dibromo-BINOL as catalyst. The reaction works with a variety of aromatic and heteroaromatic aldimines and with different alkynes, providing the expected products in generally good yields and enantiomeric excesses (up to 96%).

Asymmetric Synthesis of Fluorinated Monoterpenic Alkaloid Derivatives from Chiral Fluoroalkyl Aldimines via the Pauson‐Khand Reaction

2020

ChemInform Abstract: Calixcrowns : Synthesis and Properties

2009

The synthesis and properties of calix[n]crowns (n = 4–8), calix[n]biscrowns and their related compounds, resorcinarene crowns, have been discussed and reviewed. These macrocycles exhibit remarkable ionophoric properties toward alkali and alkaline earth metal cations, as well as, to tertiary amines. The selectivity and efficiency of calixcrowns in binding cations have been attributed to their structural features, which include substituent effects and size of the crown ether moiety and, conformation of the parent calixarene.

An analysis of the regioselectivity of 1,3-dipolar cycloaddition reactions of benzonitrile n-oxides based on global and local electrophilicity and nu…

2009

The regioselectivity of the 1,3-dipolar cycloaddition (13DC) reactions of benzonitrile N-oxides (BNOs) with electrophilic and nucleophilic alkenes has been analyzed by using global and local nucleophilicity and electrophilicity reactivity indices defined within the conceptual DFT. The BNOs react with electron-deficient and electron-rich ethylenes, but the regioselectivities of these polar reactions are different. Whereas the reactions with electron-rich ethylenes are completely regioselective, yielding 5-isoxazolines, a change in the regioselectivity is observed in the reactions with electron-deficient ethylenes, which yield a mixture of 4- and 5-isoxazolines. Analysis of the energies, geom…

Enantioselective Synthesis of α-Quaternary Amino Acids by Alkylation of Deprotonated α-Aminonitriles.

2015

A series of α-quaternary arylglycines were prepared in high optical purity (up to 98% ee) by α-alkylation of deprotonated α-aminonitriles derived by the Strecker reaction from (4S,5S)-5-amino-2,2-dimethyl-4-phenyl-1,3-dioxane. The procedure includes only chromatographic purification of the final products and is devoid of chromatography or crystallization operations on intermediates to raise the optical purity.

Stereo and regioselectivity in the phenylation of cationic allylpalladium(II) α-diimine complexes by tetraphenylborate anion

1993

The reaction of the cationic complex [Pd(4-methoxy-1,3-η3-cyclohexenyl)(py-2-CHNC6H4OMe-4)]+ (1) with BPh4− in the presence of fumaronitrile yields trans-3-methoxy-6-phenylcyclohexene (2a) and trans-4-methoxy-3-phenylcyclohexene (2b), in ca. 1 : 1 molar ratio. The trans stereochemistry of these products implies that the phenylation of the allyl ligand involves prior transfer of a phenyl group from BPh4− to the metal, followed by reductive coupling of the organic moieties. In the reactions of [Pd(η3-1,1-R1,R2-C3H3)(NN′)]+ (3) [NN′ 4-MeOH4C6NCHCHNC6H4OMe-4; py-2-CHNR (R  C6H4OMe-4, Me, or CMe3), 2,2′-bipyridine (bipy); R1  H, R2  Ph, Me; R1  R2  Me; with BPh4− in the presence of …

A stereoselective synthesis of (+)-malyngolide via a ring-closing olefin metathesis

2000

Abstract A very short and stereoselective synthesis of the non-natural enantiomer of malyngolide from l -erythrulose is described. Key features of the synthesis are the Felkin–Anh diastereoselective allylation of a polyoxygenated ketone and the allylation/metathesis/allylic oxidation protocol recently described by our group.