CONDENSATION OF TRIFORMYLMETHANE WITH HETEROAROMATIC AMINES, INCLUDING NUCLEIC-ACID BASES - A NOVEL EXAMPLE OF RING-CHAIN TAUTOMERISM

Treatment of several heteroaromatic amines, including the nucleic acid bases cytosine and adenine, with triformylmethane in pyridine at 70 d egrees C afforded 1:1 condensation products (2-11) that were character ized by H-1 and C-13 NMR spectroscopy. All the compounds were assigned as N-substituted aminomethylenemalonaldehydes, strongly preferring th e amino/keto form over the imino/enol tautomer. With cytosine and 1-me thylcytosine, unequivocal evidence for ring-chain tautomerism was addi tionally obtained: intramolecular nucleophilic attack of cytosine N3 t o one of the carbonyl carbons results in reversible cyclization to a 4 -hydroxy-4H-pyrimido[1,6-a]pyrimidin-6(7H)-one derivative (9b, 10b). I n dry methanol the corresponding O-methyl ether (12) was obtained.