Diastereoisomeric Adducts Research Articles

Resolution of α-substituted amino acid enantiomers by high-performance liquid chromatography after derivatization with a chiral adduct of o-phthalaldehyde : Application to glutamic acid analogues

The fluorescent diastereoisomeric adducts formed in a precolumn derivatization reaction of enantiomeric α-substituted amino acids with o-phthalaldehyde and N-acetyl- l-cysteine were separated by high-performance liquid chromatography on a conventional reversed-phase column. This method was particularly efficient for the complete analytical resolution of α-substituted glutamic acid analogues, such as 2-methylglutamic acid, and several cyclic analogues (1-amino-1,3-dicarboxycyclohexane, 1-amino-1,3-dicarboxy-2-cyclohexene and 1-amino-1,3-dicarboxycyclopentane). The order of elution from the column was correlated with the absolute configuration of the derivatives.

ChemInform Abstract: X=Y‐ZH Systems as Potential 1,3‐Dipoles. Part 8. Pyrrolidines and δ5‐Pyrrolines (3,7‐Diazabicyclo(3.3.0)octenes) from the Reaction of Imines of α‐Amino Acids and Their Esters with Cyclic Dipolarophiles. Mechanism of Racemization of α‐Amino Acids and Their Esters in the Presence of Aldehydes.

AbstractHeating of the imines (I) in toluene generates azomethine ylides by a prototropic shift; these undergo cycloaddition with the maleimide (IIa) or the anhydride (IIb) to give the racemic, single diastereoisomeric adducts (III).

Asymmetric synthesis of aminoacids by catalytic reduction of azlactones by substituted aminoacrylic acids. 20. Steric control in the reductive aminolysis of ?2-oxazolin-5-ones

1. PMR examination of deuterated acetylphenylalanine α-phenylethylatnide and the methyl esters of acetyl- and benzoylphenylalanine, obtained by the reductive solvolysis of 2-methyl- and 2-phenyl-4-benzylideneoxazolin-5-ones, has shown that in the reduction of oxazolinones the hydrogen undergoes cis- and trans-addition in a ratio of 1∶1. 2. Asymmetric induction in the reductive solvolysis of oxazolin-5-ones arises as a result of the fact that the proportions of cis- and trans-addition of hydrogen are different, and are strictly observed for the diastereoisomeric catalyst-substrate adducts, 3. The enantioselectivity of the reaction is determined at the stage of protonation of the semi-hydrogenated intermediate, and is independent of differentiation between the sides of the plane of the double bond at the step in which the substrate is bound.

ChemInform Abstract: High‐Pressure Approach to the Synthesis of Optically Pure Methyl 4‐Deoxyheptosides.

Abstract Recently we have described1 high pressure (4+2) cycloaddition of l-methoxybuta-1,3-diene (1)to 2,3-0-isopropylidene-D-glyceraldehyde (z), which gives rise to chiral cycloadducts 3 (Scheme). action was carried out under high-pressure conditions (22 kbar, 50°C. diethyl ether as solvent, 20 h, 80% yield)2 four diastereoisomeric adducts were formed in a ratio of 3a:3b:3c:3d=66:16:13:5. The reaction mixture was separated by column chromatography yielding two fractions which contained diastereoisomeric mixtures (3a+3b) and (3c+3d), respectively. Absolute configuration at the C-5 carbon atom in both mixtures was established by chemical correlation.' These results prompted us to use a mixture (3a+3b), being stereochemically pure at C-5 chiral center, in the synthesis of optically active methyl 4-deoxyheptosides (Scheme).

A rapid procedure for the resolution of racemic gossypol

Racemic gossypol [(±)-I] was resolved rapidly and efficiently by high-performance liq. chromatog. sepn. of the diastereoisomeric adducts of (±)-I with L-phenylalaninol on an achiral, reversed-phase, C18 column. The sepd. adducts were hydrolyzed by 2M HCl to give (+)- and (-)-I with 50-60% recovery.

High-Pressure Approach to the Synthesis of Optically Pure Methyl 4-Deoxyheptosides

Abstract Recently we have described1 high pressure (4+2) cycloaddition of l-methoxybuta-1,3-diene (1)to 2,3-0-isopropylidene-D-glyceraldehyde (z), which gives rise to chiral cycloadducts 3 (Scheme). action was carried out under high-pressure conditions (22 kbar, 50°C. diethyl ether as solvent, 20 h, 80% yield)2 four diastereoisomeric adducts were formed in a ratio of 3a:3b:3c:3d=66:16:13:5. The reaction mixture was separated by column chromatography yielding two fractions which contained diastereoisomeric mixtures (3a+3b) and (3c+3d), respectively. Absolute configuration at the C-5 carbon atom in both mixtures was established by chemical correlation.' These results prompted us to use a mixture (3a+3b), being stereochemically pure at C-5 chiral center, in the synthesis of optically active methyl 4-deoxyheptosides (Scheme).

ChemInform Abstract: ENAMINE SYNTHESIS USING THE HORNER‐WITTIG REACTION. PART 1. (AMINOMETHYL)DIPHENYLPHOSPHINE OXIDES, NEW FORMYL ANION EQUIVALENTS

AbstractDie Carbonyl‐ Verbindungen (Ia)‐(lh) lassen sich mit dem Phosphinoxid (II) in entsprechende Enamine (IV) umsetzen, dabei reagieren enolisierbare Ketone weniger zufriedenstellend.

Benzoquinones and related compounds. Part 5. Nuclear magnetic resonance study of the conformation in solution of some Diels–Alder adducts between 1,4-benzoquinones and cyclopentadiene

The Diels–Alder reaction of cyclopentadiene with the 5,6-double bond of benzyl-, α-hydroxybenzyl-, and α-acetoxybenzyl-1,4-benzoquinone, and of 1-hydroxy-1-phenyl-, 1-phenyl-, and 1-hydroxy-indan-4,7-quinone gives in each case a pair of diastereoisomeric endo adducts. For those which carry a phenyl group, the chemical shift of one of the norbornene olefinic protons in one member of each pair is significantly different from that of the corresponding proton in the other member. The conformational significance of this effect is discussed. Proton longitudinal relaxation and nuclear Overhauser relaxation techniques are used to show that the cyclopentadiene endo monoadducts of 1,4-benzoquinone and α-hydroxybenzyl-1,4-benzoquinone prefer to adopt an ‘open’ rather than a ‘closed’ conformation.

Enamine synthesis using the Horner‐Wittig reaction. Part 1. (Aminomethyl)diphenylphosphine oxides, new formyl anion equivalents

AbstractUsing the Horner‐Wittig reagent (morpholinomethyl)diphenylphosphine oxide (7), aromatic, aliphatic and α, β‐unsaturated aldehydes are converted into morpholino enamines of their homologous aldehydes. With [(N‐methylanilino)methyl]diphenylphosphine oxide (12), the same aldehydes, together with the ketones (cyclic as well as acyclic, both saturated and α, β‐unsaturated), are converted into enamines of their homologous aldehydes. Both types of enamines are converted into the corresponding aldehydes by mild, acid‐catalyzed hydrolysis, showing the utility of 7 and 12, as formyl anion equivalents. Preparation of each geometrical isomer of the N‐methylanilino enamines is possible since the intermediate diastereoisomeric adducts 13 can be separated.

Aspects of nitrile oxide cycloaddition stereoselectivity: Chemistry of 4-cyano-2,2-dimethyl- and 4-cyano-2,2,5,5-tetramethyl-1,3-dioxolane oxides. X-ray structure of (4 [formula omitted], 5 [formula omitted])-4,5-bismethoxy-carbonyl-3-[(4 [formula omitted])-2,2,5,5-tetramethyl-1,3-dioxolan-4-yl]-Δ 2-isox-azoline

4-Cyano-2,2-dimethl- and 4-cyano-2,2,5,5-tetramethyl-1,3-dioxolane oxìdes (1) and (2) were generated from the corresponding chloro-oximes, and trapped by addition to styrene, dimethyl maleate, dimethyl fumarate, and cyclopentene. The additions to styrene and dimethyl fumarate gave 1 : 1 mixtures of diastereoisomeric adducts. However some stereoselectivity was detected in the additions to the cis -1,2-disubstituted alkenes. The structure of (4 RS , 5 RS )-4,5-bismethoxycarbonyl-3- [(4 RS )-2,2,5,5-tetramethyldioxolan-4-yl]-Δ 2-isoxazoline (17) was established by an X-ray structure determination.

The use of 119Sn NMR for the investigation of organotin reactions

. 119 Abstract — Direct Sn NMR has been employed as a very useful tool for the investigation of a variety of organotin reactions. The high sensitivity of tin chemical shifts to small structural changes has been used for discrimi— nation between closely related isomers. Thus asymmetric hydrostannation of unsaturated chiral esters has been studied by means of the direct analysis of diastereoisomeric adducts in reaction mixtures. The three different configurational isomers of tetra—sec—butyltin have been distinguished and the results used for stereochemical study of electrophilic cleavage of the tin—carbon bond. Also other asymmetric induction processes have been evalua— ted. Alternatively nJ(SflD) coupling constants, which are very easily observed after suitable deuterium labelling, have given access to very fruitful information. The Karplus—like angular dependence of 3J(SnD) has been employed to determine the stereochemistry of several organotin Diels—Alder cycloadditions as well as the stereochemistry of alkene hydrostannations. For instance major cZn-t-L—addition was found in the hydrostannation of phenyl— cyclohexene while 4qn—addition was dominant in the case of norbornene derivatives. The stereochemistry and the regioisomerism of alkyne hydrostanna— tion has also been examined. Finally a complex analytical problem involving the regioselectivity and stereochemistry of the stannylation of allyl tosylates has been solved by the joint consideration of tin chemical shifts and coupling constants.

Structurally isomeric and diastereoisomeric adducts from the nitration of 1,2,4-trimethylbenzene. Orientation and mechanism of side-chain substitution of arenes

Structurally isomeric and diastereoisomeric adducts from the nitration of 1,2,4-trimethylbenzene. Orientation and mechanism of side-chain substitution of arenes