A-Amino-y-hydroxycarboxylic

A suspension of Pd-C in ethyl acetate vigorously stirred under H2 until uptake of gas ceased, a soln. of /r 5-2-azidocyclohexanol and di- ert-butyl dicarbonate in the same solvent added, and the mixture stirred at room temp, under H2 for 19 h - product. Y 71%. Pre-saturation of the catalyst is important to prevent nitrile formation. F.e. incl. N-protected a-amino-p-hydroxycarboxylic acid esters and 2-acoxyamines, s. S. Saito et al.. Tetrahedron Letters 30, 837-8 (1989). 

For the a-alkylation of //-hydroxy- or //-amino-substituted y-lactones the preparation of a dianionic species is required. This methodology was first used with /J-hydroxycarboxylates and became an important, highly stereoselective, preparative step (see Section 1.1.1.3.2.1.1.1.2.). 

The following cases should be distinguished caramelization in the presence of (a) an inorganic acid, (b) an organic acid as the catalyst, and (c) either a-, y-, or < hydroxycarboxylic acid as the catalyst. In the last case, such acids may form lactides or lactones, respectively, under the caramelization conditions. Our preliminary results suggested that such acids participate in the formation of secondary aromas similarly to 0 -amino acids. This problem will be discussed separately in the section devoted to certain food aromas in which carbohydrates are involved. In either case when organic acids are... 

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