Aza-analogues of pteridine. Part I. 1,2,4,6,8-Penta-azanaphthalene and some methyl, dihydro-, and 5-alkoxy-derivatives

Abstract

Synthetic routes to 1,2-dihydro-1,2,4,6,8-penta-azanaphthalene and its mono-, di-, and tri-methyl derivatives have been developed. Oxidation by silver oxide in aprotic media gave the fully aromatic 1,2,4,6,8-penta-azanaphthalenes (pyrimido[5,4-e]-as-triazines), of which the 3-methyl-, 3,7-dimethyl, and 3,5,7-trimethyl derivatives were sufficiently stable for complete characterization. Covalent addition of methanol to those aromatic compounds lacking a 5-methyl group gave 5,6-adducts which were isolated and dehydrogenated by silver oxide to the corresponding 5-methoxypenta-azanaphthalenes. 1H N.m.r. spectra confirmed the structures and those of two products, 9-amino-2,6-dimethylpurine and 4,6-dimethyl-7-nitro-1,2,3a,5-tetra-azaindene, formed abnormally from appropriate 4-hydrazinopyrimidines and triethyl orthoformate. The u.v. spectrum of each penta-azanaphthalene in cyclohexane exhibited a well defined n→π* transition band with centre ca. 500 mµ.