Achiral Alcohols Research Articles

Efficient methods for the preparation of alkyl-aryl and symmetrical or unsymmetrical dialkyl ethers between alcohols and phenols or two alcohols by oxidation-reduction condensation.

Oxidation-reduction condensation via alkoxydiphenylphosphines (diphenylphosphinite esters) (1), generated in situ from chlorodiphenylphosphine (2) and alcohols, 2,6-dimethyl-1,4-benzoquinone (3), and phenols proceeds smoothly to afford alkyl-aryl ethers in good to high yields under neutral conditions. In a similar fashion, a new and efficient method for the preparation of symmetrical or unsymmetrical dialkyl ethers in good to high yields is established via tetrafluoro-1,4-benzoquinone (fluoranil) (4), alcohols, and 1 formed in situ from (n)BuLi-treated alcohols and 2. This method is applicable also to the etherification of chiral secondary or tertiary alcohols with retention or inversion of configurations. The inverted ethers are afforded by treating chiral alkoxydiphenylphosphines and achiral alcohols, while the reaction of achiral alkoxydiphenylphosphines and chiral alcohols forms retained ethers.

Alcohol-O,O'-dibenzoyl-(2R,3R)-tartaric acid complexes.

Structures of chiral and achiral alcohol-O,O'-dibenzoyl-(2R,3R)-tartaric acid (DBTA) complexes were investigated by single-crystal X-ray diffraction (seven new crystal structures were determined). The complexes contain DBTA and chiral alcohol in 1:1, DBTA and achiral alcohol in 1:2 host-guest stoichiometry. The hydrogen bonding structures of chiral alcohol-DBTA and achiral alcohol-DBTA complexes are different, but within a subclass they are isostructural ones.

Thermoanalytical Study of O,O'-Dibenzoyl-(2R,3R)-Tartaric Acid Supramolecular Compounds. Part I. Investigation of compounds with water, achiral alcohols and phenols

Thermal behaviour of O,O'-dibenzoyl-(2R,3R)-tartaric acid (DBTA), its monohydrate, and its potential supramolecular compounds with achiral alcohols and phenols were investigated with TG, DSC, EGD. The structural differences among the anhydrous DBTA, its monohydrate, and the supramolecular derivatives were investigated with X-ray powder diffraction. The thermal behaviour of DBTA-supramoleculars with isopropyl, tert-butyl, and 5-cyclohexyl alcohols is found to be similar to each other but essentially different from that of both DBTA and its monohydrate. On heating they melt and decompose between 60–180°C while they loose in one or two steps the bound alcohol. The thermal stability of the supramolecular compounds increases with the boiling point of the alcohol component. According to the X-ray powder diffraction patterns each supramolecular substance has different structure, that may also result in the different thermal stability of the compounds. The molar ratio of DBTA:achiral alcohol samples is 1:1.01–1:1.57 estimated from the corresponding mass losses. The XRD patterns of the prepared two DBTA-phenol materials are different from those of DBTA-achiral alcohol samples. The phenol compounds melt with slow mass losses and give an endothermic peak between 73–83°C but the melting point of the anhydrous DBTA cannot be observed. DBTA:phenol molar ratio is estimated to be 1:0.41 and 1:0.65 for phenol and 2-methylphenol, respectively.

Thermoanalytical Study of O,O'-Dibenzoyl-(2R,3R)-Tartaric Acid Supramolecular Compounds Part II. Investigation of the resolution of racemic alcohols

The resolution of three chiral alcohols with O,O'-dibenzoyl-(2R,3R)-tartaric acid (DBTA) via diastereoisomeric supramolecular compound formation was investigated with thermoanalytical methods. On the basis of TG measurements the DBTA:chiral alcohol molar ratio in the compounds is 1:1 which agrees with the results of single-crystal X-ray diffraction analysis. The DBTA – chiral alcohol supramolecular compounds have different supramolecular structure than the DBTA – achiral alcohol supramolecular compounds. The supramolecular compounds containing cyclohexanols have higher thermal stability than the compounds containing acyclic aliphatic alcohols. The amount of unreacted DBTA monohydrate in the solid phase can be determined both with DSC and with TG measurements.

Catalytic enantioselective protonation of a samarium enolate with fluorous chiral and achiral proton sources in fluorous biphasic systems

Enantioselectivities near maximum values were obtained in the catalytic reaction by a ropid addition of a fluorous achiral alcohol (Rfh 3COH) to the reaction mixture: for DHPEX in Rfh 3COH/THF solid-liquid biphase system and for a fluorous chiral alcohol in THF/FC-72 liquid-liquid biphase system.

NMR Verification of Helical Conformations of Phycocyanobilin in Organic Solvents

AbstractSelective NMR decoupling and nuclear Overhauser effect (NOE) experiments with phycocyanobilin (PCB) show proton‐proton interactions between the terminal rings A and D, viz. the chiral C(2) methine center and the ethyl substituent at C(18), as a result of the helical conformation of this open‐chain tetrapyrrole in solution. Quantitative NOE measurements and a combination of force‐field and semiempirical calculations (FSC) afford inter‐proton distances across the helical gap of 4.2–4.6 (NOE) and 3.2–4.2 A° (FSC). The NOE and FSC, in conjuction with a qualitative evaluation of the steric interactions in the two optimized helices, suggest furthermore that, in solution, the helix M is somewhat more stable than P. The coexistence of at least two diastereoisomers is corroborated also by the circular dichroism (CD) spectra of PCB in MeOH/EtOH which point to a temperature‐dependent equilibrium in solution, and by a considerable increase of this CD upon changing the solvent from the achiral alcohols to ethyl (−)‐(S)‐lactate which reflects a selective solvent‐induced CD differentiating between diastereoisomers.

The First Tri- and Tetraalkoxysilanes with Four Different Substituents.

Unsymmetrically substituted tri- and tetraalkoxysilanes were surprisingly found to be configurationally stable and easy to prepare. It was found that compounds of type MeSi(OR)(2)(OR'), MeSi(OR)(OR')(OR"), Si(OR)(2)(OR')(2), Si(OR)(2)(OR')(OR"), Si(OR)(3)(OR'), and even Si(OR)(OR')(OR")(OR) could be obtained by sequential addition of a variety of chiral and achiral alcohols to methyltrichlorosilane or tetrachlorosilane in the presence of pyridine. In the case of MeSi(OR)(OR')(OR") and Si(OR)(OR')(OR")(OR), two types of compounds that have never been prepared before, were obtained in good yield.

(+)-Pinoresinol synthase: A stereoselective oxidase catalysing 8,8′-lignan formation in Forsythia intermedia

8,8′-Lignan skeletal formation is engendered by (+)-pinoresinol synthase, an oxidase catalysing the stereoselective coupling of two achiral E-conifery alcohols to give (+)-pinoresinol in > 97% enantiomeric excess.

Fluorescence Characterization of the Cyclodextrin/Pyrene Complex Interaction with Chiral Alcohols and Diols

The chiral properties of cyclodextrins (CDs) facilitate the formation of diastereomeric complexes with a number of pesticides and pharmaceuticals which are also frequently composed of one or more chiral centers. The roles of chirality and structural volume in CD binding to a homologous series of linear, chiral alcohols and diols are evaluated by comparing the trend in the pyrene fluorescence I/III band ratio and the hydrophobicity for the CD/pyrene complex with CD/pyrene complexes incorporating achiral alcohols. Stronger hydrophobicity is observed for complexes capped by chiral alcohols relative to complexes formed with a similar achiral counterpart, suggesting the importance of the alcohol chiral center. Furthermore, the diols induce a more hydrophobic environment than their alcohol counterparts with the β-CD/pyrene complex, while the converse is the case for the γ-CD systems. The systems involving γ-CD were also compared by use of pyrene fluorescence lifetime measurements.

A NEW ENANTIOSELECTIVE ASYMMETRIC SYNTHESIS OF TRI-CO-ORDINATE PHOSPHORUS COMPOUNDS FROM DI-CO-ORDINATE λ3-ARYL(ALKYL)IMINOPHOSPHINES

Abstract The reaction of di-co-ordinate λ3-aryl(alkyl)iminophosphines (1) with achiral alcohols in the presence of optically active tertiary amines has been found to proceed in an asymmetric way affording optically active O-alkyl amidophosphonites (2). N-(2,4,6-Tris-t-butylphenyl)amido-O-methyl-phenyl-phosphonite (2a) was obtained in this way with 55% ee and the absolute configuration (S) was chemically linked with (+)-(R)-O-methyl t-butanephosphonothioic acid.

CHIRAL HYDRIDE REAGENTS CONTAINING (R/S)-2,2′-DIHYDROXY-6,6′-DIMETHYLBIPHENYL FOR REDUCTION OF ALKYL PHENYL KETONES

Abstract Chiral hydride reagents for asymmetric reduction were prepared from LiAlH4, optically pure 2,2′-dihydroxy-6,6′-dimethylbiphenyl (1), and an achiral alcohol. They showed high enantioface discrimination in the reduction of prochiral alkyl phenyl ketones. The configuration of preferentially formed enantiomer always agreed with that of 1 used for the reagents. Further, polymeric reagents containing (R)-1 moiety were prepared and their behavior in the reduciton was described also.

Asymmetric transfer hydrogenation of prochiral α-methyl-crotonic acid by achiral and chiral alcohols with a binuclear ruthenium diphosphine complex

Asymmetric transfer hydrogenation of prochiral α-methyl-crotonic acid by achiral and chiral alcohols with a binuclear ruthenium diphosphine complex

ChemInform Abstract: OPTICALLY ACTIVE TRIVALENT PHOSPHORUS ACIDS ESTERS, AN APPROACH BY ASYMMETRIC SYNTHESIS

AbstractDie Umsetzung der Phosphor(III)‐chloride (I) mit den Alkoholen (II) in Äther bei ‐70°C ergibt in Gegenwart des optisch aktiven Amins (IV) die optisch aktiven Ester (III).

Optically active trivalent phosphorus acids esters: an approach by asymmetric synthesis

The reaction of chiral PIII chlorides with achiral alcohols or thiols in the presence of optically active tertiary amines gives the hitherto unknown optically active trivalent phosphorus acids esters, the absolute configuration and optical purity of which was determined chemically by conversion into known phosphine oxides or phosphonodithioates.

Asymmetric synthesis of sulphinic esters with the sulphur atom as a sole chirality centre

The reaction of sulphinyl chlorides with achiral alcohols in the presence of optically-active tertiary amines has been found, by means of 1H n.m.r. spectroscopy using a chiral europium complex, to give optically-active sulphinates with optical purity up to 45%.

Asymmetric selection during dehydration of achiral alcohols in the presence of (+)-camphorsulphonic acid

Individual dehydration of four achiral alcohols, (I), (II), (IV), and (V), in the presence of (+)-camphorsulphonic acid resulted in the formation of optically active olefin in each case.