Pyrazine chemistry. Part 14. On the preparation and oxygenation of pyrazines and some reactions of the product peroxides

Abstract

Some new methods for preparing substituted pyrazines are reported. 2,6-Dimethoxy substituted pyrazines undergo facile addition of singles oxygen to form endoperoxides, some of which are remarkably stable. The behaviour of these compounds has been explored. In particular, deoxygenation is effected with triphenylphosphine to induce skeletal rearrangements, the pyrazines undergoing ring contraction to substituted imidazoles. The rearrangement occurs via intermediate oxadiazepines which can be intercepted by intramolecular trapping with a pendant hydroxy group, leading to a novel method for entry into the 3,6,1-oxadiazecine system. Reductive cleavage of the peroxide bond leads to unstable dihydroxydihydropyrazines.