Esters directed syntheses, -dipolar

Alkylation of malonic esters and other active methylene compounds is useful in synthesis because the alkylated products can be subjected to hydrolysis and decarboxylation (1.10). Direct decarboxylation under neutral conditions with an alkali metal salt (e.g. lithium chloride) in a dipolar aprotic solvent (e.g. DMF) is a popular alternative method. ... 

General. Diphenyl phosphorazidate is a readily available, nonexplosive, and relatively stable azide widely used as a reagent in peptide synthesis, " and as a versatile reagent in a wide array of organic transformations. DPPA has been successfully utilized in the synthesis of a-amino acids and o-aryl carboxylic acids direct preparation of thiol esters from carboxylic acids and thiols the stereospecific preparation of alkyl azides and the phosphorylation of alcohols and amines The application of DPPA in a modified Curtius reaction permits a simple one-step conversion of carboxylic acids to urethanes under mild reaction conditions. DPPA acts as a nitrene source, and can undergo 1,3-dipolar cycloaddition reactions. The Curtius degradation of carboxylic acids in the presence of f-butanol gives the Boc-protected amine directly (eq 1). 

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