2(1H)-PYRAZINONES AND 2H-1,4-OXAZIN-2-ONES AND THEIR USE IN HETEROCYCLIC SYNTHESIS

The synthesis and functionalization of 3,5 dichloro-2(1H)pyrazinones a nd the corresponding 2H-1,4-oxazin-2-ones is described. The use of the ir multifunctionalized 2-azadiene system in cycloaddition reactions wi th electron-rich and electron-poor dienophiles and subsequent eliminat ions from the adducts of alkynes or nitriles is discussed. In this way pyridine or pyrazine derivatives can be obtained. Application of an i ntramolecular version of the cycloaddition-elimination process is show n to yield c-anellated 2(1H)pyridin(on)es from 2(1H)pyrazinones anchor ed with an appropriate side chain in position 3 or 6. The specific com bination of a 2-azadiene system, 3-chlorimine group and a reactive lac tone function in the 2H-1,4-oxazin-2-ones is demonstrated to generate specifically substituted oxazoles, triazoles and tetrazoles on reactio n and further conversion with specific nucleophiles. The mechanism of these processes is briefly mentioned together with their application i n the synthesis of nucleoside or alkaloid-type compounds.