Acid-catalysed methanolysis

In mixed anhydrides in which thiophosphoryl phosphorus is bonded to another heteroatom other than phosphorus, attack by a nucleophile may be diverted away from the phosphorus should the second reactive centre be more electrophilic. So, in the case of phos-phinothioic sulphonic anhydrides, although hydrolysis or acid-catalysed methanolysis of 101 (X = H) proceeds with inversion at phosphorus, attack by HO occurs at sulphur with retention of configuration of phosphorus whilst the hydrolysis of the much more reactive 101 (X = F) in aqueous dioxane proceeds with preponderant inversion of phosphorus... 

The stereoselectivity of the uncatalysed 0-1 methylation of free sugars with diazomethane has been correlated with the preferred conformations of the thermodynamically favoured anomers. More specific studies of methyl glycosides relate to the acid-catalysed methanolysis of a-D-glucofuranose 1,2 3,5-bis(phenylboronate), which gives the a- and 3-glucofuranosides in the ratio of... 

The H and n.m.r. of the Ca complex of A -glycolylneuraminic acid at pH 7 showed that a 1 1 complex is formed. Analysis of electric field shifts gave the approximate position of the ion shown in formula (14). The interactions of Na", Ca ", and La " with methyl glycofuranosides in methanol have been studied by measurement of the rate of acid-catalysed methanolysis in the presence of chlorides. Rates decreased with increasing ionic charge. The conclusion was reached that steric requirements for complex formation with metal ions differ even when the ionic radius is approximately the same and that the main factor is charge, to which is related the ability to deform the furanoside. ... 

Selective acid>catalysed methanolysis of 2,3,2, 3 -tetra-0-benzyl-4,6 4, 6 -di-0-benzylidene-a,a-trehalose gave the monoacetal which was converted into the dimesylate and from this 6-deoxy-6-fluoro-a,a-trehalose was obtained. In the course of the work 4-chloro-4,6-dideoxy-6-fluoro-a-D-galactopyranosyl a-D-glucopyranoside was produced (as a derivative), and 6-iodo, 6,6 -di-iodo, 6-azido-, and 6,6 -diazido-trehalose compounds were also prepared. 6-Deoxy-6-fluoro- and 6-deoxy-6-iodo-trehalose were also obtained by way of the... 

Deuterated fatty acids can be separated from non-deuterated in part at least on WCOT columns coated with polar stationary phases [693,695], t-Butyldimethylsilyl ester derivatives (see Chapters 4 and 7) are useful for GC-mass spectrometric estimation of these compounds [692,709,1004], Long-chain dicarboxylic acids have been separated by GC and identified by GC-MS in the semm of patients suffering from Reye s syndrome [663] and in the lipids of royal Jelly [542,543], Brominated vegetable oils are added to soft drinks to disperse flavouring agents after acid-catalysed methanolysis, the methyl ester derivatives of fatty acids containing two, four and six bromine atoms have been separated on packed [538] or fused silica [151] columns with non-polar silicone stationary phases. 

Base-catalysed anonerisation of some acetylated 2,4-dinitrophenyl j9-D-glucopyranosides was determined to occur by nucleophilic attack at the ipse-position,and acid-catalysed methanolysis of the methyl D-glucofuranosides led to anomerisation and also, unlike in the case of the pyranosides, to the formation of the dimethylacetal. 

Paulsen s group has reported the synthesis of derivatives (256) and (257) of the hydroxyethyl-branched octose that is found as a component of the quinocycline complexes isolated from Streptomyces aureofaciens. The route from the epoxyketone (255) is outlined in Scheme 59. An identical route was used to prepare branched-chain analogues in the o-series, in which it was shown that acid-catalysed methanolysis of the hydroxyethyl-branched derivative (258) yielded the more stable isomer (259) via the anhydro-sugar d-(257). Paulsen s group has also described a synthesis of a derivative (260) of pillarose (see Vol. 9, p. 99), a component of the antibiotic pillaromycin, using the dianion (261) prepared from 2-hydroxymethyl-l,3-dithiane to introduce the branch at C-4 (Scheme 60). A similar approach, using the anion derived from 2-methyl-l,3-dithiane, and subsequent desulphurization and reduction, etc., was adopted in a synthesis of a derivative (262) of aldgarose (4,6-dideoxy-3-C-[(i )-l-hydroxyethyl]-D-W6o-hexopyranose 3,3 -cyclic carbonate) (cf. Vol. 8, p. 100). 

Contactor-type polymeric membrane reactors have been also applied to liquid-phase reactions other than hydrogenation or oxidation. The hydration of a-pinene has been carried out successfully over polymeric membranes consisting of mixed matrixes of PDMS embedded USY or beta zeolites or sulfonated activated carbon. The membranes were assembled in a flat contactor-type reactor configuration, separating the aqueous and organic phases. Sulfonated PVA membranes were also reported to be effective in the acid catalysed methanolysis of soybean oil carried out in a flat contactor-type membrane reactor configuration. ... 

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