Diastereoselective Alkylation Reactions Research Articles

Aziridinyl Anions from a Chiral, Nonracemic 2‐Isopropylidineaziridine: Surprisingly Diastereoselective Alkylation Reactions.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Diastereoselective Alkylation and Aldol Reactions Mediated by the D‐Mannitol‐Derived Oxazolidin‐2‐one as a Chiral Auxiliary.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Aziridinyl anions from a chiral, nonracemic 2-isopropylidineaziridine: surprisingly diastereoselective alkylation reactions.

Lithiation and alkylation of a 2-isopropylidineaziridine bearing an (S)-alpha-methylbenzyl group on nitrogen proceeds with high levels of diastereocontrol (80-90% de).

Introduction of a New Chiral Oxazolidin‐2‐one Derived from D‐Mannitol and Its Applications as a Chiral Auxiliary.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Introduction of a New Chiral Oxazolidin-2-one Derived from D-Mannitol and Its Applications as a Chiral Auxiliary

Chiral oxazolidin-2-one is easily prepared from D-mannitol and demonstrated to undergo highly diastereoselective alkylation reactions via lithium imide Z-enolates of its N-acyl derivatives to afford <TEX>${\alpha}-branched$</TEX> products. Evans syn and non-Evans sy n aldol products were also selectively obtained using this new auxiliary in high diastereomeric purity by simply changing the stoichiometry of TiCl4 and the nature of the amine base. Also, this new auxiliary is employed in diastereoselective Staudinger-type <TEX>${\beta}-lactam$</TEX> syntheses. Using 2-chloro-1-methylpyridinium iodide as the dehydrating agent, the reaction of auxiliary tethered acetic acid with trans imines gave the desired <TEX>${\beta}-lactams$</TEX> with cis-selectivity.

DIASTEREOSELECTIVE ALKYLATION AND ALDOL REACTIONS MEDIATED BY THE d-MANNITOL-DERIVED OXAZOLIDIN-2-ONE AS A CHIRAL AUXILIARY

ABSTRACT Chiral N-acylated oxazolidin-2-ones readily available from d-mannitol have been demonstrated to undergo highly diastereoselective alkylation reactions via their lithium imide Z-enolates to afford α-branched products. Evans syn and non-Evans syn aldol products were also selectively obtained using this new auxiliary in high diastereomeric purity by simply changing the stoichiometry of TiCl4 and the nature of the amine base.

Preparation of α-amino-carboxylic acid derivatives via diastereoselective reactions of glycine enolate equivalents

Protected glycine analogues tethered to an imidazolidinone auxiliary undergo diastereoselective alkylation and acylation reactions in moderate to good yields (9–91%) with high levels of stereocontrol (generally >95% de). Subsequent alkylation of these derivatives has been demonstrated for the production of non-racemic α,α-disubstituted amino acid precursors. Diastereoselective aldol reactions are also found to proceed with good yields and excellent stereocontrol (62–84%, 93–95% de). Chiral auxiliary cleavage and hydrogenolysis of these adducts affords the β-hydroxy-α-amino acid derivatives with no observed erosion of optical purity.

ChemInform Abstract: Highly Diastereoselective Alkylation of a Pyroglutamate Derivative with an Electrophile Obtained from Indole. Synthesis of a Potential Intermediate for the Preparation of the Natural Sweetener (-)-Monatin.

Abstract The synthesis of a potential intermediate for the preparation of the very intensive sweetening agent (-)-Monatin is described. The synthesis is based on a highly diastereoselective alkylation reaction of a pyroglutamate derivative with an electrophile obtained from indole.

Highly Diastereoselective Alkylation of a Pyroglutamate Derivative with an Electrophile Obtained from Indole. Synthesis of a Potential Intermediate for the Preparation of the Natural Sweetener (-)-Monatin

The synthesis of a potential intermediate for the preparation of the very intensive sweetening agent (-)-Monatin is described. The synthesis is based on a highly diastereoselective alkylation reaction of a pyroglutamate derivative with an electrophile obtained from indole.

Design, synthesis, resolution, and application of a highly efficient chiral auxiliary: Cis-2-amino-3,3-dimethyl-1-indanol

The chiral amino alcohol, cis-2-amino-3,3-dimethyl-1-indanol was synthesized and resolved. Its oxazolidinone derivative was found to be a highly efficient chiral auxiliary in diastereoselective alkylation, acylation, bromination, and hydroxylation reactions.

Synthesis and asymmetric alkylation of glucose-derived bicyclic oxazinones: An evaluation of their use as “chiral glycines”

We have prepared structurally novel bicyclic oxazinones based on D-glucopyranose. The lithium enolates of these compounds undergo highly diastereoselective alkylation reactions with reactive alkyl halides, in modest yields. Use of the phosphazene P4 base enhances the yields of these processes, suggesting that metal enolate aggregation is at least partly responsible for the depressed yields. The stereochemistry of the products has been unequivocally ascertained by nOe measurements and ab initio calculations.

D-xylose derived oxazolidin-2-ones as chiral auxiliaries in stereoselective alkylations

Chiral N-acylated oxazolidin-2-ones readily available from D-xylose have been demonstrated to undergo highly diastereoselective alkylation reactions via their lithium imide enolates to afford α-branched products. These are easily purified and hydrolyzed without difficulty allowing isolation of the desired ramified carboxylic acids in high enantiomeric excesses and to return the auxiliaries for reuse. Inexpensive glyco-oxazolidin-2-one derivatives prepared from D-xylose have been used in stereoselective α-alkylation reactions to get branched carboxylic acids in high enantiomeric purities.

Synthese und Reaktionen chiraler, von (R)-(?)-bzw. (S)-(+)-2-Methoxymethylpyrrolidin abgeleiteter Dithiocarbamate

Synthesis and Reactions of Chiral Dithiocarbamates Derived from (R)-(−)- or (S)-(+)-2- The synthesis, diastereoselective alkylation reactions, dithiocarboxylation, and aldol condensation of several substituted methyl (R1CH2) (S)-2-(methoxymethyl)-pyrrolidine-1-dithiocarboxylates (S)-2 and of the corresponding (R)-derivatives (R)-2 are described. The new enantiomeric dithiocarbamates (S)-2a–e, and (R)-2a–d are obtained by reaction of (S)-(+)-[(S)-1] or (R)-(−)-2-(methoxymethyl)-pyrrolidine [(R)-1], respectively, with carbon disulfide in dry methanol/anhydrous sodium acetate and the appropriate alkylating agent. The cyclic ketene dithioacetals (S)-3 and (R)-3 are formed by dithiocarboxylation procedure of (S)-2a and (R)-2a whereas (S)-6 and (R)-6 are obtained by aldol reaction with isobutyraldehyde. (S)-2c,d and (R)-2c,d react in a diastereoselective manner after deprotonation with n-BuLi or LiTMP/LiBr at −78°C in THF with alkyl halides to the enantiomeric compounds 4a/ent-4a, 4b/ent-4b and 5/ent-5, respectively.

ChemInform Abstract: Diastereoselective Alkylation Reactions Employing a Camphor‐Based Chiral Oxazinone Auxiliary.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Diastereoselective alkylation reactions employing a camphor-based chiral oxazinone auxiliary

An almost complete π-face selectivity is obtained in asymmetric alkylation reactions of lithium enolates derived from imide 2 which contains a camphor-based chiral oxazinone auxiliary.

ChemInform Abstract: Asymmetric Synthesis of (+)‐ and (‐)‐Coniines and (‐)‐Sedamine by Diastereoselective Alkylation Reaction of Ethoxypiperidinone.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Alkylation and protonation of chiral schiff bases: Diastereoselectivity as a function of the nature of reactants

The factors controlling the diastereoselective alkylation and protonation reactions of chiral Schiff bases prepared from 2-hydroxypinan-3-one and α-aminoesters are reported: nature of the ester, of the alkylating agent and of the base.

Asymmetric Synthesis of (+)- and (-)-Coniines and (-)-Sedamine by Diastereoselective Alkylation Reaction of Ethoxypiperidinone

Diastereoselective alkylation reaction of the chiral 6-ethoxypiperidinones (4) and (5) has been developed and successfully applied to the asymmetric synthesis of piperidine alkaloids, (+)- and (-)-coniines (11) and (12), (-)-sedamine (21), and (-)-allosedamine (22)

ChemInform Abstract: Highly Diastereoselective Alkylation Reactions of Vinylogous Urethanes Derived from Simple Tetronic Acids.

Abstract The lithium enolates generated from the tetronic acid derived vinylogous urethanes 3 and 4 have been found to undergo alkylation reactions with a variety of electrophiles to give products with predictable stereochemistry accompanied by very high diastereoselectivity.

Highly diastereoselective alkylation reactions of vinylogous urethanes derived from simple tetronic acids

The lithium enolates generated from the tetronic acid derived vinylogous urethanes 3 and 4 have been found to undergo alkylation reactions with a variety of electrophiles to give products with predictable stereochemistry accompanied by very high diastereoselectivity.