Diastereoselective Addition Of Organometallic Reagents Research Articles

Synthesis of fluorinated pseudopeptides: metal mediated reversal of stereochemistry in diastereoselective addition of organometallic reagents to N-(tert-butanesulfinyl)-α-fluoroenimines

The addition reaction of organometallic reagents to N-(tert-butanesulfinyl)-α-fluoroenimines was studied. Depending of the nature of the organometallic species (Grignard reagents or zincate complexes), we were able to control the configuration of the newly created stereogenic centers in high yields with good to high diastereomeric ratios. The chiral β-fluoro allylamines are key synthons toward the synthesis of fluorinated pseudopeptides bearing a fluoroolefin moiety as a peptide bond mimic.

ChemInform Abstract: Diastereoselective Addition of Organometallic Reagents to Chiral Imines and 1,3-Oxazolidines.

ChemInform 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.

ChemInform Abstract: Enantio- and Diastereoselective Addition of Organometallic Reagents to Aldehydes and Imines

ChemInform Abstract: Enantio- and Diastereoselective Addition of Organometallic Reagents to Aldehydes and Imines

ChemInform Abstract: Diastereoselective Addition of Organometallic Reagents to Diimines Derived from (R,R)‐1,2‐Diaminocyclohexane and Aromatic Aldehydes.

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 Addition of Organometallic Reagents to Diimines Derived from (R,R)-1,2-Diaminocyclohexane and Aromatic Aldehydes

The double addition of organolithium compounds and allylzinc bromide to the imines prepared from (R,R)-1,2- diaminocyclohexane by condensation with aromatic and heteroaromatic aldehydes gave secondary diamines with high yields and diastereoselectivities apart for the reaction of 2-pyridinealdehyde derivative which occurred with low to moderate stereocontrol. Keywords: Amine, 1,2-diaminocyclohexane, diastereoselectivity, imine, organometallic reagents

Highly diastereoselective addition of organometallic reagents to a trifluoroacetaldehyde hydrazone derived from ( R)- N-benzylphenylglycinol

Organolithium and Grignard reagents add efficiently with very high stereoselectivity (>98% de) to a trifluoroacetaldehyde hydrazone derived from ( R)- N-benzylphenylglycinol. The addition proceeds on the re face of the chelated hydroxyhydrazone providing the ( R)-α-trifluoromethylated amine after hydrogenolysis.

ChemInform Abstract: Asymmetric Synthesis of Diarylmethylamines by Diastereoselective Addition of Organometallic Reagents to Chiral N‐tert‐Butanesulfinimines: Switchover of Diastereofacial Selectivity.

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.

ChemInform Abstract: Asymmetric Syntheses of New Functionalized β‐Amino Alcohols via Diastereoselective Addition of Organometallic Reagents onto Oxazolidines.

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.

Asymmetric synthesis of diarylmethylamines by diastereoselective addition of organometallic reagents to chiral N- tert-butanesulfinimines: switchover of diastereofacial selectivity

Diastereoselective addition of organometallic reagents to chiral N- tert-butanesulfinimines gave alkylated adducts in high yields and diastereoselectivities. Cleavage of the chiral auxiliary under mildly acidic conditions gave diarylmethylamines in high yield. A reversal in the diastereoselectivity was observed by using either phenylmagnesium bromide in toluene or phenyllithium in THF. The use of the same chiral auxiliary thus allowed the synthesis of both enantiomers of a number of diarylmethylamines.

Asymmetric syntheses of new functionalized beta-amino alcohols via diastereoselective addition of organometallic reagents onto oxazolidines.

Diastereoselective reactions between (S)-phenylglycinol-derived oxazolidines and two unsaturated organolithium reagents afforded chiral beta-amino alcohols having vinyl and alkynylsilane moieties. When the same reactions were performed in the presence of titanium isopropoxide, a dramatic change of regioselectivity was observed, from the alpha- to the gamma-position, thus producing beta-amino alcohols with allyl or allenylsilane functions. A rationalization of the observed diastereoselectivity was suggested for each case.

Nucleophilic additions to (4S)-1-alkylidene-2,4-dihydro-1H-pyrazino[2,1-b]quinazoline-3,6-diones

Investigation of the title compounds as didehydro amino acid templates showed their lack of reactivity against amines or Grignard reagents under copper(I) catalysis, but efficient additions to the exocyclic double bond took place with mercaptides or stabilized carbanions. Regio- and diastereoselective addition of organometallic reagents occurred at the C(3)-position and, in 1-methylene derivatives, these reactions were followed by a rearrangement of the intermediate oxy-anion to give pyrido[2,1-b]quinazolines.

Chiral Oxime Ethers in Asymmetric Synthesis. 3.1 Asymmetric Synthesis of (R)-N-Protected α-Amino Acids by the Addition of Organometallic Reagents to the ROPHy Oxime of Cinnamaldehyde

A new asymmetric synthesis of α-amino acids is described in which the key step is the diastereoselective addition of organometallic reagents to (R)-O-(1-phenylbutyl)cinnamaldoxime 5 to give hydroxylamines 6. Subsequent reductive cleavage of the N−O bond in the hydroxylamine 6 followed by N-protection gave the carbamates 7, which upon oxidation with ruthenium(III) chloride/periodate gave the N-protected amino acids 8. The method was also adapted to the synthesis of a quaternary amino acid 15 from the ketoxime ether 9.

Regioselective and diastereoselective addition of organometallic reagents to (S )-N-[(2-pyridyl)methylene]-O-(trimethylsilyl)valinol. Synthesis of (S )-1-(2-pyridyl)alkylamines

The imine prepared by condensation of pyridine-2-carbaldehyde and (S)-valinol, followed by protection of the hydroxy group as its trimethylsilyl ether, undergoes addition of organometallic reagents at either the carbon and/or nitrogen atom of the CN double bond. Primary alkylmagnesium halides (R = Et, Bu, cyclohexylmethyl) add preferentially at nitrogen to give tertiary amines. By using hex-5-enylmagnesium bromide as a probe for the single-electron-transfer mechanism, only the N-(hex-5-enyl) adduct is obtained. Other Grignard reagents RMgX (R = Me, Pri, Bn, allyl, vinyl, Ph) and organolithium and zincate reagents add at the carbon atom to give the secondary amines as the main or exclusive regioisomers. Ketimines are the main by-products in the reactions of methyl-, isopropyl- and vinyl-magnesium halides, (isopropyl)dimethylzincate and tert-butylmetal reagents. With the latter reagents, other by-products are also observed, presumably coming from C,N-dialkylation of the CN double bond and attack on the pyridine ring. The C-alkylation products are formed with excellent or perfect diastereoselectivity (si face attack), apart from the tert-butyl and benzyl reagents; then, after acidic work-up, the (S,S)-amino alcohols are converted to (S)-1-(2-pyridyl)alkylamines by oxidative cleavage of the auxiliary. The superior asymmetric induction provided by O-(trimethylsilyl)valinol as auxiliary, with respect to valine esters, is rationalized on the basis of the lower basicity of the oxygen atom. Polar and radical mechanisms, explaining the formation of regioisomeric products and by-products, are discussed.

ChemInform Abstract: A New Synthesis of Chiral α‐Substituted Furfuryl Amines by Diastereoselective Addition of Organometallic Reagents.

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.

A new synthesis of chiral α-substituted furfuryl amines by diastereoselective addition of organometallic reagents

A new method to prepare chiral α-substituted furfuryl amines was achieved in high d.e. values and chemical yields.

ChemInform Abstract: Highly Diastereoselective Addition of Organometallic Reagents to Chiral Imines Derived from 1‐(2‐Methoxyphenyl)ethylamine.

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.

Highly Diastereoselective Addition of Organometallic Reagents to Chiral Imines Derived from 1-(2-Methoxyphenyl)ethylamine

Highly Diastereoselective Addition of Organometallic Reagents to Chiral Imines Derived from 1-(2-Methoxyphenyl)ethylamine

ChemInform Abstract: Diastereoselective Addition of Organometallic Reagents to Norephedrine‐ Derived 2‐Acyl‐N‐tosyloxazolidines.

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.

Asymmetric syn‐Selective Michael Addition of Enolates to Chiral 8‐Phenylmenthyloxy Vinyl Chromium Carbene Complexes

AbstractMichael addition reactions of ketone and ester lithium enolates to optically active Fischer vinylcarbene complexes derived from (‐)‐8‐phenylmenthol take place with high syn selectivity and high levels of asymmetric induction. The initial Michael adducts can be further elaborated through diastereoselective addition of organometallic reagents to ketones and aldol reactions. Removal of the metal fragment and chiral auxiliary group leads to cyclic enol ethers with three or five contiguous stereogenic centers and of high enantiomeric purity.

Diastereoselective Addition of Organometallic Reagents to Nor-Ephedrine-Derived 2-Acyl-N-Tosyl-Oxazolidines

Diastereoselective Addition of Organometallic Reagents to Nor-Ephedrine-Derived 2-Acyl-N-Tosyl-Oxazolidines