In the presence of an amine, carboxylic acids are converted to acyl azides which undergo a modified Curtius reaction in the presence of an alcohol to give alkyl carbamates directly. With t-butanol, the resulting t-butyl carbamates can readily be converted to the free amines with mild acid. Malonic half-esters, e.g. Ethyl- hydrogen malonate, give ɑ-amino acid derivatives: J. Am. Chem. Soc., 94, 6203 (1972); Chem. Pharm. Bull., 22, 1398 (1974); J. Org. Chem., 49, 185 (1984). Use of the hindered base 1,8-Bis(dimethyl-amino)-naphthalene, enables the isocyanate intermediates to be isolated: Synth. Commun., 23, 335 (1993). Application to ɑ?-unsaturated acids provides a useful degradation to aldehydes with one C atom fewer by hydrolysis of the intermediate enamine. See, e.g.: Synth. Commun., 20, 589 (1990).
