Synthesis and reactivity of new beta-enamino acid derivatives: A simple and general approach to beta-enamino esters and thioesters

A new strategy has been developed for the synthesis of several beta-enamino acid derivatives. N,N'-Carbonyldiimidazole has been used as C-acylating ag ent of methyl ketimines, providing a direct and simple route to new beta-en amino carbonyl imidazole derivatives 2. These derivatives 2 were cleanly an d efficiently transformed into beta-enamino esters 4 (X = O) and thioesters 4 (X = S) by reaction with a great variety of alcohols and thiols, includi ng tertiary ones. Alternative and complementary routes to compounds 4 were also investigated. In addition, beta-keto esters 6 have been obtained by mi ld acid hydrolysis of beta-enamino esters 4.