An improved method for the asymmetric protonation of enolates with chiral α-sulfinyl alcohols/trifluoroethanol

Enantioselective protonation of 2-methyl tetralone enolate using a stoichiometric amount of 2-sulfinyl alcohol (S,R_s)-1 as a chiral proton donor yields the corresponding chiral ketone with a high level of enantioselectivity, provided that the chiral proton donor (CPD) is regenerated with an achiral proton source (APS). In contrast, stereoselectivity was only moderate if catalytic CPD (0.2 equiv.) and an APS are used.     

Prediction of the vaporization enthalpy based on modified Randi? indices. I. Monohydric alcohols

The vaporization enthalpy of monohydric alcohols with different structures under normal conditions is calculated using a modified Randič method with an error comparable to the experimental one. The energy of hydrogen bonds in alcohols is determined and shown to be constant and independent on the alcohol structure. Original Russian Text Copyright ? 2009 by E. L. Krasnykh __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 50, No. 3, pp. 577–581, May–June, 2009.     

Prediction of the vaporization enthalpy based on modified Randič indices. II. Polyatomic alcohols

The vaporization enthalpy of polyatomic alcohols with different structures under normal conditions is calculated using a modified Randič method. The vaporization enthalpy of polyatomic alcohols is shown to largely depend on the number of hydrogen bonds formed by alcohols.     

Alkaloids of Nitraria komarovii. XI. Structure of komavicine and the products of the dehydrogenation of the nitrarine method of dehydrogenation in the quinolinyl-β-carboline series

The new alkaloid komavicine has been isolated from the epigeal part ofNitraria komarovii, and its structure has been established on the basis of spectral characteristics and chemical transformations. The products of the dehydrogenation of nitrarine with selenium and sulfur have been studied. A method has been developed for the dehydrogenation of dihydro and tetrahydro derivatives in the quinolinyl--carboline series.Institute of Chemistry of Plant Substances, Uzbekistan Academy of Sciences, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 33–39, January–February, 1993.     

Selective lipase-catalyzed acylation of epimeric α-sulfinyl alcohols: an efficient method of separation

A facile and efficient separation of mixtures of epimeric α-sulfinyl alcohols 2:3 can be accomplished by selective lipase-catalyzed acylation with neat vinyl acetate. Pseudomonas cepacia and Candida rugosa lipase showed opposite epimer differentiation in the esterification.     

Vapour–liquid equilibria of dimethyl carbonate with linear alcohols and estimation of interaction parameters for the UNIFAC and ASOG method

Isobaric vapour–liquid equilibria have been experimentally determined for the binary systems methanol+dimethyl carbonate, ethanol+dimethyl carbonate, dimethyl carbonate+1-propanol, dimethyl carbonate+1-butanol and dimethyl carbonate+1-pentanol at 101.3 kPa. The activity coefficients were calculated to be thermodynamically consistent and were correlated with the Wilson and UNIQUAC equations. Interaction parameters related to the carbonate group (OCOO) and alcohols, in ASOG and UNIFAC methods, have been determined using our experimental VLE data. The experimental results, as well as those by other authors, agree with the calculated VLE using the new ASOG and UNIFAC parameters.     

Synthesis of new enantiomerically pure β-amino alcohols of the pinane series

A series of new β-amino alcohols with pinane structure, (+)- and (?)-3α-amino-10β-pinan-4β-ols, 4β-amino-10β-pinan-3α-ol, and 4α-amino-10β-pinan-3α-ol have been synthesized with the goal of using them as organocatalysts in the aldol reaction of isatin with acetone.     

A general method for the synthesis of enantiopure aliphatic chain alcohols with established absolute configurations. Part 2, via catalytic reduction of acetylene alcohol MαNP esters

A general method for synthesizing enantiopure (100% ee) aliphatic alcohols with established absolute configurations has been developed and applied to alcohols CH₃(CH₂)_n–CH(OH)–(CH₂)_mCH₃, the enantiomeric discrimination of which is the most difficult, if m = n + 1 and n is large. Racemic saturated alcohols with short chains could be directly enantioresolved as (S)-(+)-2-methoxy-2-(1-naphthyl)propionic acid (MαNP acid) esters by HPLC on silica gel, and their absolute configurations were simultaneously determined by ¹H NMR diamagnetic anisotropy. However, the application of this powerful MαNP ester method to alcohols with long chains was difficult, because of smaller values of the separation factor α. In such cases, the use of the corresponding acetylene alcohol MαNP esters was crucial. Acetylene alcohol MαNP esters were largely separated by HPLC on silica gel, and their absolute configurations were unambiguously determined by ¹H NMR as reported in the Part 1 paper. The MαNP esters obtained with established absolute configurations were catalytically hydrogenated to yield saturated alcohol MαNP esters. It was evidenced that no racemization occurred at the stereogenic center of the alcohol moiety during catalytic hydrogenation, by the coinjection of MαNP esters in HPLC. From the MαNP esters obtained, enantiopure (100% ee) aliphatic chain alcohols with established absolute configurations were recovered. Although the [α]_D values of these alcohols were too small for the identification of the enantiomers, it was clarified that the analytical HPLC of MαNP esters is useful for identification in most cases.     

Preparation and oxidation of α-nitro alcohols with supported reagents.

Preparation of 2-nitro alkanols has been achieved by condensation of aldehydes with nitroalkanes in the presence of alumina-supported potassium fluoride. Nitroketones are produced by oxidation of nitroalkanols with montmorillonite - supported chromium trioxide.     

Diastereoselectivity in the Carroll rearrangement of β-keto esters of tertiary allylic alcohols

Carroll rearrangement of β-keto esters derived from tertiary allylic alcohols, for example, 7, under basic conditions followed by decarboxylation of the resulting β-keto acids yielded the expected γ,δ-unsaturated methyl ketones 8 with a range of olefin geometries from 100:0 to 1:1.8 E/Z, depending on the relative steric requirements of the two groups at the allylic center.     

Study of the enantioselectivity of the CAL-B-catalysed transesterification of α-substituted α-propylmethanols and α-substituted benzyl alcohols

A study of the enantioselectivity exhibited by the lipase B from Candida antarctica in the transesterification of different α-substituted α-propylmethanols with vinyl acetate is shown. The best results are obtained when the large-sized (L) substituent of the alcohol is either a phenyl group or more especially a cyclohexyl group, although the reaction rates are lower than when linear or slightly branched groups are present. It is also found that ramification at the β-position of the L substituent has a deleterious effect on both lipase activity and enantioselectivity. Moreover, some α-substituted benzyl alcohols bearing medium-sized (M) substituents larger than an ethyl and smaller than a propyl group are resolved by means of this methodology with moderate-good enantioselectivities (E=46–57) and similar reaction rates.     

Congested molecules. Where is the steric repulsion? An analysis of the electron density by the method of interacting quantum atoms

The computed electron density of several congested saturated hydrocarbons and halogenated derivatives has been analyzed by the method of interacting quantum atoms (IQA). For all the molecules studied, the calculations show the existence of a bond path between the congested atoms and which, according to the Quantum Theory of Atoms in Molecules, indicates that there is a stabilizing interaction between these atoms. The bond path is found to exist up to interatomic distances well‐beyond the sum of the van der Waals radii. The IQA results indicate that steric hindrance is not a repulsive force between the congested atoms but that is the result of an increase in the intra‐atomic or self‐energy of the congested atoms. This increase in self‐energy is caused by the deformation of the atomic basin of the congested atoms. © 2013 Wiley Periodicals, Inc.     

New method for studying the reactivities of α-diazo imines. Investigation of the cyclization of N-substituted 2-diazoacetamidines to 1,2,3-triazoles

N-Substituted diazoacetamidines were generated in the reaction of N-substituted acetamidines with benzenesulfonyl azide. It is shown that their cyclization to isomeric 1,2,3-triazoles characterizes the reactivities of -diazo imines. The synthesis of 5-amino-1,2,3-triazole derivatives was accomplished, and their ¹H, ¹³C, and ¹⁵N NMR spectra were studied.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 775–782, June, 1991.     

Ir-catalysed formation of C-F bonds. From allylic alcohols to α-fluoroketones

A novel iridium-catalysed tandem isomerisation/C-F bond formation from allylic alcohols and Selectfluor? to prepare α-fluorinated ketones as single constitutional isomers is reported.     

About the limits of regularization and the ansatz method

The well-known adsorption integral equation (AIE) for calculating pore size and adsorption energy distributions from adsorption isotherms on porous solids is, from the mathematical point of view, a linear Fredholm integral equation of the first kind and therefore an ill-posed problem. What can we realistically expect from the solution of such an ill-posed problem by regularization? Does it make sense to restrict the number of possible solutions by the so-called ansatz method? In this paper, the two methods for solving ill-posed problems are from scratch explained and illuminated by concrete examples. Their relevance and fundamental limitations are discussed.     

roposed method can effectively eliminate the effects of

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