Reaction kinetics, sugar-amine

Although the exact mechanism of the reaction is difficult to resolve, from our accumulated data we can propose a mechanism which explains the experimental results obtained and enables the prediction of the stereochemistry of the sulfinate formed, based on the steric volume of the amine. The experimental data clearly demonstrate that the diastereoselective formation of a sulfinate is base-dependent. Therefore, the proposed mechanism has to include the effect of the base on the stereocourse of the reaction. Some additional circumstances have to be taken into account (1) the reaction of sulfiny 1 chlorides with alcohols in the presence of bases does not proceed via a sulfine intermediate117 (2) Mislow has proved that the reaction of chiral alcohols with sulfinyl chlorides in the presence of a base is kinetically controlled814,83 and (3) on first inspection, one could imagine the extreme case where DAG, under the influence of the base, reacts with only one of the enantiomeric sulfinyl chlorides. However, this is not the case, because the same yield and ee are obtained when 1.2 or 2.0 equiv of MeSOCl are used. Accordingly, the first step of the process could be an equilibrium reaction involving the sulfinyl chloride and the base. The racemic sulfinamide formed would be the active sulfur species that interacts with the sugar derivative. 

Closely related to this reaction is the base-catalyzed epimerization of aldonic acids and their lactones (see Lundt and Madsen, this voL). This reaction is, of course, even older than the LdB-AvE process, and was first used by Emil Fischer [29]. Potassium hydroxide and tertiary amines (pyridine, quinoline) have been used as bases. The reaction is much slower than the epimerization of sugars and requires prolonged heating, but the aldonic acids are much more stable to the action of bases than the sugars, and no side reactions occur. The reaction proceeds even if the hydroxyl group at C-2 is methylated [30]. The kinetics and the mechanism of the interconversion of the aldopentonic acids in potassium hydroxyde solution have been studied this reaction also occurs via the enediol and the removal of H-2 is the rate-determining step [31]. It is of industrial importance, as indicated by numerous patents [32]. 

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