Loss Of Optical Purity Research Articles

An efficient access to ( R)- and ( S)-6,6′-dimethoxy-2,2′-diiodo-1,1′-biphenyl

In a better procedure than the known for (rac)- 2a, the diamine (rac)- 2b was resolved for the first time with the new resolving agent ( R, R)- and ( S, S)-2,3-di(phenylamino-carbonyl)tartaric acid ( 5c) (40–45% weight yields; >99% ee). The diamines ( R)- or (S)- 2a and 2b were converted with >98% stereochemical retention into the diiodides ( R)- and (S)- 3a and 3b and subsequently, without loss of optical purity, diphenylphosphinated to the known diphosphines ( R)- and (S)- 4a and 4b.

Optically active chromium(III) complexes VIII. Chiroptical and epimeric forms of chloro(1,2-diaminoethane) (1,4,8-triazaoctane)chromium(III) complexes and the structural characterization of some pentachloroantimonate(III) salts

Racemic- exo-mer-[CrCl(en)(2,3-tri)]ZnCl 4 has been resolved using potassium antimonyl tartrate. The less soluble {−} 447- exo-mer-[CrCl(en)(2,3-tri)][Sb 2(tart) 2]·4H 2O (orthorhombic, P2 12 12 1, a = 12.800(3), b = 12.881(3), c = 16.712(4) A ̊ , V = 2755.4(11) A ̊ 3 , Z = 4) is shown by single crystal X-ray analysis to have the ( R)-configuration at the coordinated sec-NH center. Addition of HCl to the mother liquor results in the isolation of rac-exo-mer-[CrCl(en)(2,3-tri)]SbCl 5 (orthorhombic, Pbca, a = 14.055(3), b = 10.472(2), c = 26.510(5) A ̊ , V = 3901.8(13), Z = 8 ) and further addition of ZnCl 2 allows the isolation of (+)-( S)- exo-mer-[CrCl(en)(2,3-tri)]ZnCl 4. Exo-mer-[CrCl(Me 2tn)(3,3-tri)]SbCl 5·H 2O·0.5HCl (monoclinic, Cc, a = 16.002(2), b = 11.627(5), c = 27.571(6) A ̊ , β = 99.79(2)°, V = 5055(3) A ̊ 3, Z = 8 ) has also been obtained from the crude chloride salt using potassium antimonyl tartrate and 6M HCl. Both SbCl 5 2− salts contain isolated SbCl 5 2− anionic units. Rac-exo-mer-[CrCl(en)(2,4-tri)ZnCl 4 has been converted into rac-endo-mer-[CrCl(en)(2,3-tri)ZnCl 4 (monoclinic, P2 1/c, a = 11.682(2), b = 13.915(2), c = 10.809(2) A ̊ , β = 93.31(2)°, V = 1781.2(5) A ̊ 3, Z = 4 ) by base hydrolysis. Treatment of (−)-( R)- exo-mer-[CrCl(en)(2,3-tri)]ZnCl 4 with NH 3(liq.) and sodium amide results in the formation of {−} 450-( R)- exo-mer-[Cr(NH 3)(en)S(2,3-tri)] 3+ (isolated as the Hg 2Cl 7 3− salt) but with considerable loss of optical purity. We have also confirmed the orientation of the chelated aminomethylpyridine (ampy) ligand in exo-mer-[CrCl(ampy)(2,3-tri)HgCl 4·H 2O (monoclinic, P2 1/c, a = 11.867(5), b = 10.2780(10), c = 17.318(5) A ̊ 3, Z = 4 ) has having the −CH 2NH 2 arm trans to the coordinated chloro ligand.

ChemInform Abstract: Synthesis of (S)‐2‐Amino‐1,1‐diphenylbutan‐4‐ol; Conversion of an . alpha.‐Amino Acid into an α‐(Diphenylmethyl) Amine Without Loss of Optical Purity.

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 Stereochemical Study of the Isomerization of Cyclopropyl Ethers to Allyl Ethers Catalyzed with Zinc Iodide.

Optically active 1-alkoxybicyclo[4.1.0]heptane was converted using zinc iodide as a catalyst to 2-alkoxymethylidenecyclohexane without loss of optical purity. The mechanism of the isomerization was studied using a stereochemical analysis of the product and deuterium labeling experiments. The results indicated that the isomerization takes place through a stepwise mechanism that involves an attack of zinc iodide on the cyclopropane ring to cause ring opening, followed by an intramolecular 1,2-hydride shift with liberation of the zinc iodide.

Synthesis of (S)-2-Amino-1,1-diphenylbutan-4-ol; conversion of an α-amino acid into an α-(diphenylmethyl) amine without loss of optical purity

The title amino-alcohol 4 is an intermediate for the preparation of chiral bicyclic amidines and guanidines, and also for polyamines with potential as ligands in enantioselective catalysis. It has been synthesized from (S)-methionine 1 via (S)-homoserine lactone 2 and amino-diol 3. Hydrogenolysis of the doubly benzylic hydroxyl group in 3 proved non-trivial, but was eventually achieved through the application of catalytic transfer methodology to the bis-acetyl derivative 14.

An Expedient Route to Optically Pure 3-endo-Hydroxydicyclopentadiene

Optically pure 3-endo-hydroxydicyclopentadiene has been prepared expediently in both enantiomeric forms via lipase-mediated kinetic resolution. Manganese dioxide transforms the optically active 3-endo-alcohol into the highly versatile chiral building block 3-oxo-dicyclopentadiene without loss of optical purity.

General and Versatile Approach to the Synthesis of Optically Active 5- Alkylpiperazine-2-carboxylic Acids

General and convenient syntheses of optically active 5-alkylpiperazine- 2-carboxylic acids are described. The methods are based on cyclization of L- or D-serine with α-amino acids and occur without loss of optical purity. The presented procedures are based on readily available starting materials and can be arranged for multigram quantities

Optically Active Alkylvinylpyridines: Synthesis of (+)-(S)-6-(1-Methylpropyl)-2-Vinylpyridine

Abstract A generalizable procedure for the preparation of optically active 6-alkyl-2-vinylpyridines from chiral 2-alkylpyridines without loss of optical purity is reported.

Stereocontrol in intermolecular nucleophilic addition to N-acyliminium ion directed by a bicyclo(2.2.1)heptene or 7-oxabicyclo(2.2.1)heptene group. A novel route to 5-substituted 3-pyrrolin-2-ones of high optical purity.

Intermolecular nucleophilic additions to the conformationally rigid, tricyclic pyrrolidinium ion (derived from 2 or 6) took place exclusively from the less-hindered face fused with its bicyclo[2.2.1]heptene or 7-oxabicyclo[2.2.1]heptene moiety. Retro-Diels-Alder fragmentation of the resulting chiral 7-oxabicyclo[2.2.1]heptene system furnished a 5-substituted 3-pyrrolin-2-one without a loss of optical purity.

Chiral Ligands Containing Heteroatoms; 9.1General Procedures for the Synthesis of Optically Active 1-(2-Pyridyl)alkylamines from α-Amino Acids

General syntheses of 1-(2-pyridyl)alkylamines and N-methyl or N,N-dimethyl-1-(2-pyridyl)alkylamines from optically active α-amino acids are described. The presented procedures are based on catalyzed co-cyclotrimerization of the suitable nitriles with acetylene, which can be conducted without loss of optical purity

Preparation of chiral aziridines from chiral oxiranes with retention of configuration

Chiral oxiranes are converted into chiral aziridines viaβ-hydroxyalkly aryl sulfides and then β-tosylaminoalkyl aryl sulfides without loss of optical purity and with overall retention of configuration.

Highly effective asymmetric synthesis of 11-deoxydaunomycinone and analogues

Optically active 11-deoxydaunomycinone and its 9-hydroxymethyl analogue were synthesized in 95% e.e. by means of tandem Michael/Diels–Alder reaction as a key step in the tetracycle's formation. As a reagent, a chiral pentadienyltin was prepared without loss of optical purity from ethyl 2-[(S)-1-hydroxyethyl]pent-4-enoate, which was obtained in 97% e.e. by reduction (yeast) of the corresponding acetoacetate derivative. The chirality on the tin reagent was transferred to the C-9 of 11-deoxydaunomycinone via diastereoselective epoxidation in high efficiency. For the synthesis of the 9-hydroxymethyl analogue of 11-deoxydaunomycinone, enantioselective epoxidation was applied to the allylic alcohol moiety of the tetracyclic quinonoid compound to afford the corresponding optically active epoxide in high chemical and optical yield. Success in this highly efficient and enantioselective epoxidation was attributed to the protection of the phenolic hydroxy group in the substrate from competitive co-ordination to the Sharpless reagent.

ChemInform Abstract: Organoaluminum‐Promoted Rearrangement of Epoxy Silyl Ethers to β‐Siloxy Aldehydes.

AbstractThe title rearrangement of epoxy silyl ethers such as (I) or (III) is achieved using a bulky organoaluminum reagent to give the products (II) and (IV) without loss of optical purity.

Enantioselective carbon-carbon bond formation by chiral organotitanium compounds ; Methyltitanium (S)-N-acylpyrrolidinylmethoxide diisopropoxides.

New chiral compounds, (S) -N-acylpyrrolidinylmethanols (1b-f and 1h), were synthesized and chiral methyltitanium diisopropoxides (2a-h) were prepared from 1a-h. Enantioselective carbon-carbon bond formation between aromatic carbaldehydes and 2a-h was achieved in yields of 90-97% and 10.5-54.1%ee. The chiral auxiliaries (1a-h) were recovered in almost quantitative yields without any loss of optical purity.

Light‐Induced and Thermal π‐Skeletal Rearrangement of Heptalenes with Retention of Configuration

AbstractIt is shown that dimethyl 5, 6, 8, 10‐tetramethyl‐ (3) and 8‐ (tert‐butyl)‐5,6,10‐trimethylheptalene‐1, 2‐dicarboxylate (5), and their derivatives rearrange reversibly on irradiation or on heating to yield the corresponding 1,6,8,10‐tetramethyl‐ (4) and 8‐(tert‐butyl)‐1,6,10‐trimethylheptalene‐1,2‐dicarboxylate (6), and their derivatives by double‐bond shift (π‐skeletal rearrangement) via a transition state with D2 symmetry as the highest possible one. This follows from the fact that (−)‐(P)‐3 is photochemically as well as thermally rearranged to give (−)‐(P)‐4 i.e. the π‐skeletal rearrangement occurs with retention of configuration of the heptalene skeleton and without loss of optical purity.

A stereospecific synthesis of chiral 1,3-disubstituted bromoallenes

Optically active 1, 3-disubstituted propargyl alcohols undergo SNi′ rearrangements with thionyl bromide in the presence of propylene oxide to yield bromoallenes without loss of optical purity.

Synthesis of d-amicetose and l-rhodinose from l-glutamic acid

l-Glutamic acid has been converted into a separable mixture of d-amicetono- and l-rhodinono-γ-lactones by a sequence involving transformation into ( S)-γ-carboxy-γ-butyrolactone ( 2), conversion of 2, conversion of 2 into the corresponding methyl ketone by the diazoketone route, and selective reduction with zinc borohydride or borane-methyl sulfide. Reduction of the two lactones with di-isobutylaluminium hydride gave the corresponding deoxy sugars. In spite of some improvements in the preparation of 2, the optical yield of this step was only ∼80%, but one crystallisation from chloroform raised the optical purity to 96%. The subsequent steps produced a loss in optical purity of only 4%.

(S)-o-N-(N-benzylprolyl)aminobenzaldehyde and (S)-o-N-(N-benzylprolyl)aminoacetophenone as reagents for asymmetric synthesis of threonine

Chiral aldehydes and ketones, derivatives of proline and piperidine-2-carboxylic acid have been synthesized and their Schiff bases with glycine form copper complexes which were hydroxyethylated with acetaldehyde; decomposition of the complexes obtained gave threonine with an optical purity of up to 97–100% and with threo/allo ratios of up to 19 : 1, and the chiral reagents can be recovered and reused with no loss of optical purity of the threonine.

Factors in the formation of isomerically and optically pure alkyl halides. Part IX. Reactions of (1-substituted n-alkyl) diphenylphosphinites with hydrogen halides and with halogens

1-Substituted n-alkyl chlorides and bromides are obtained in high yield, and with no detectable rearrangement, by the interaction of the corresponding alkyl diphenylphosphinites with hydrogen halides or with halogens at 0–20 °C. A slight tendency to the formation of rearrangement products is shown in the iodide systems, although products of at least 99.5% purity are obtainable if the reaction time is restricted. Optically active 2-chloro-octane is readily obtained with no loss in optical purity, although the bromide and iodide are liable to undergo some racemization after their initial formation.

Criterion of Mechanism based on Optical Rotation and Rearrangement in Alkyl Groups during Formation of Alkyl Halides

THE geometrical and electronic requirements of replacement reactions designated SN2, SN1 and SNi were described by Ingold and Hughes on the basis of kinetics and changes in optical rotation1. Recent work2,3, however, has shown the need for caution in the practice which afterwards became fashionable of assigning these classifications on the basis of the optical result, unsupported by kinetic data, in other types of reaction, such as replacement of hydroxyl by halogen. The only unequivocal decision in such a reaction would seem to be the assignment of the exclusive SN2 process to account for the isolation of, for example, optically pure (−)-2-chloro-octane from (+)-2-octanol. Isolation of the optically pure (+)-halide, retained configuration, does not necessarily point to the SNi, internal, mechanism, since this result could be due to a double SN2 process, the first one being independent of halogen. Predominant inversion but with some loss in optical purity could be due to (SN2 + SN1 + SNi) or (SN2 + SN1) or (SN2 + SNi), whereas predominant retention could be due to (SN2 + SNi + SN1) or (SN1 + SNi) or (SN2 + SNi), bearing in mind that the effect ascribed to SNi could be due entirely or partly to the double SN2.