SYNTHESES OF THE PRINCIPAL BREAD FLAVOR COMPONENT, 6-ACETYL-1,2,3,4-TETRAHYDROPYRIDINE, AND ACETAL PROTECTED PRECURSORS

Various synthetic approaches towards the principle bread flavor component, 6-acetyl-1,2,3,4-tetrahydropyridine, and some of its more stable acetal and enol ether derivatives have been developed by elaboration and ring closure of appropriately functionalized imines. The aza-Wittig type cyclization of functionalized delta-azido ketones, carrying an acetal function at the alpha'-position, proved to be the most successful route. The synthetic scheme leading to the labile bread flavor component incorporates (1) a regioselective acetalization of a nonsymmetric alpha-dione and (2) an entry into stable protected acetal derivatives. An alternative to the required delta-chloroketone, carrying an acetal function at the alpha'-position, consisted of selective hydrolysis of the corresponding delta-chloro-imine. In addition, some N-alkylated analogues of the Maillard flavor compound have been synthe-sized. Alternative approaches towards acetal protected 2-acetyltetrahydropyridines involved initial azidation of delta-chloroimines, selective hydrolysis of the imino function in the presence of an acetal moiety and intramolecular aza-Wittig type formation of cyclic imines.