Showing papers in "Journal of Organic Chemistry in 1977"

Nuclear magnetic resonance determination of enantiomeric composition and absolute configuration of .gamma.-lactones using chiral 2,2,2-trifluoro-1-(9-anthryl)ethanol

Abstract: or elucidating the structures of natural products. Chiroptic methods are useful for determining absolute configurations of some lactones depending upon the substitution patterns.1 X-ray structural analysis is valuable (in the case of suitably crystalline materials) but time consuming and hence expensive. In this paper, we describe an NMR method for simultaneously determining absolute configurations and enantiomeric purities of -lactones that is, in principle, applicable regardless of substitution pattern. Chiral aryltrifluoromethylcarbinols, 1, are known to render the NMR spectra of enantiomers “nonequivalent” for a

Rates of thiol-disulfide interchange reactions between mono- and dithiols and Ellman's reagent

Abstract: The rate constants for thiol-disulfide interchange between 21 mono- and dithiols and Ellman's reagent correlate with the pKu's of the thiol groups with a Bronsted coefficient of p = 0.36. The maximum rates ofreduction are observed for thiols having pK, values close to the pH of the solution in which the reactions were carried out. In the dilute solutions examined (10-4-10-6 M in each reagent), the rate of the second, intramolecular interchange step in reactions of dithiols was faster than that of the first, intermolecular interchange, regardless of the size of the cyclic disulfide formed. A convenient synthesis of a mixture of diastereomers of 1,4-dimercapto-2,3-butanediol (i.e., of a mixture of dithiothreitol, DTT, and dithioerythritol, DTE) has been developed from 1,2:,4-diepoxybutane and thiolacetic acid.

Fluorination with molecular fluorine. A convenient synthesis of 2-deoxy-2-fluoro-D-glucose

Abstract: A method is described for the direct conversion of 3,4,6-tri-0-acetyl-D-glucal to 3,4,6-tri-0-acetyl-2-deoxy-2-fluoro-..cap alpha..-D-glucopyranosyl fluoride (I) and 3,4,6-tri-0-acetyl-2-deoxy-2-fluoro-..beta..-D-mannopyranosyl fluoride (II) by reaction with F/sub 2/. I and II hydrolyze to 2-deoxy-2-fluoro-D-glucose and 2-deoxy-2-fluoro-D-mannose. The method can be used to prepare I and II in yields of 35 and 26%, respectively. (BLM)

A simple preparation of phenols from diazonium ions via the generation and oxidation of aryl radicals by copper salts

Abstract: The standard method of preparation of phenols from diazonium salts consists of heating the latter in highly acidic aqueous solution; the high temperature and acidity often cause a variety of unwanted side reactions. We advocate an entirely different procedure which can be performed in a few minutes in neutral solution at room temperature, or below. The method is based on our previous observation that aryl radicals can be oxidized to phenols by cupric ion and it consists of adding cuprous oxide to a dilute solution of the diazonium salt dissolved in a solution containing a large excess of cupric nitrate. In one case the presence of siIver(1) appeared to accelerate the radical oxidation. Not only is the redox procedure simpler than the thermal method, but in all cases studied to date, the yields are equivalent or superior to those obtained by the thermal procedure. In four cases in which the latter is unsatisfactory, the redox method is quite successful and it is considered the method of choice for new cases.