Pteridine studies. Part XLIV. Self-condensation of some methylpteridines, and reactions with other nucleophiles

Abstract

Treatment of 6,7-dimethylpteridine with aqueous alkali and with aliphatic amines gave 7-(3,4-dihydro-6,7-di-methylpteridin-4-ylmethyl)-3,4-dihydro-4-hydroxy-6-methyl-(1) and 7-(6,7-dimethylpteridin-4-ylmethylene)-3,7-dihydro-6-methyl-pteridine (3a), respectively. 7-Methylpteridine and an amine similarly produced 3,7-di-hydro-7-(7-methylpteridin-4-ylmethylene)pteridine (3b).

6,7-Dimethylpteridine and hydroxylamine yielded 3-hydroxyiminomethylamino-5,6-dimethylpyrazine-2-carbal-dehyde oxime (9a). 2,6,7-Trimethylpteridine and methoxyamine afforded 2-(1 -methoxyimino)ethylamino-3-methoxyiminomethyl-5,6-dimethylpyrazine (9b). Malononitrile reacted with (a) 6,7-dimethyl- and 2,6,7-tri-methyl-, (b) 4-methyl-, and (c) 4,6,7-trimethyl-, and 2,4,6,7-tetramethyl-pteridine to give, respectively, (a) the 2,3-dimethyl (13)(from the first two). (b) the 8-methyl (15), and (c) the 2,3,8-trimethyl (16) derivatives of 6-amino-pyrido[2,3-b]pyrazine-7-carbonitrile. Cyanoacetamide and 6,7-dimethylpteridine yielded 6-amino-2,3-di-methylpyrido[2,3-b]pyrazine-7-carboxamide (14).

Dimedone, malonamide, and methanol (the last named only under acidic conditions) added to 6,7-dimethylpteridine across the 3,4-double bond to give 4-substituted 3,4-dihydro-6,7-dimethylpteridines [respectively (18a and b) and (17)]. 2-Methylpteridine and dimedone gave 3,4-dihydro-2-methyl-4-(4.4-dimethyl-2,6-dioxocyclo-hexyl)pteridine (18c). With ethyl acetoacetate, 2-methyl- and 4-methyl-pteridine yielded 2-methyl (19a) and 4-methyl derivatives of ethyl 5,5a,8a.9-tetrahydro-7-methylfuro[2,3-g]pteridine-8-carboxylate (19b), respectively. 4-Methylpteridine added two molecules of benzylamine across the 5,6- and 7,8-double bonds to give 6,7-bis-(benzylamino)-5,6,7,8-tetrahydro-4-methylpteridine (21 ).

Consideration of the u.v. spectra of the dimedone adducts (18a, c, and d) revealed that the neutral species were zwitterionic.

U.v. and ¹H n.m.r. spectra are reported and discussed.