Bisorthoesters as Polymer Intermediates. III. Oligomers Containing Purine Rings

Hexa-n-propyl orthoisophthalate, hexa-n-propyl orthoterephthal-ate, and in one case hexaethyl orthooxalate were condensed with aminomalondiamine dihydrochloride or aminomalonamideamidine dihydrochloride in DMSO or DMF between 100°C and the boiling point of DMF to oligomers containing adenine and hypoxanthine rings. For example, hexa-n-propyl orthoisophthalate and amino-malonamidamidine dihydrochloride in dimethyl sulfoxide at 100°C gave an oligomer of poly (2,8-hypoxanthinediyl-1,3-phenylene). The condensation was limited to oligomers of relatively low molecular weight, partly because of the low solubility of the oligomers under reaction conditions and partly also because the four reactive amino groups of the aminomalonamideamidine and the aminomalondiamidine did not react simply as difunc-tional tetramines to form linear aromatic polymers; this unequal reactivity of the amine functions caused side reactions to occur. Such side reactions have not been observed in the reactions of bisorthoesters with tetrafunctional aromatic orthodiamines, such as 3,3′,4,4′-tetraaminobiphenyl.