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■ Condensed as-Triazine II: Synthesis of 7-Phenyldihydro- and Tetrahydropyrazino[2,3-e]-as-triazines

Kuan-Han Lee, Bor-Ruey Huang, Yeh-Long Chen, and Cherng-Chyi Tzeng*

*School of Chemistry, Kaohsiung Medical University, 100 Shin Chuen 1st Rd., Kaohsiung 80708, Taiwan, R.O.C.

Abstract

Certain derivatives of dihydro- and tetrahydropyrazino[2,3-e]-as-triazines were prepared by ring closure of 5,6-diamino-as-triazines with phenylglyoxal in methanol. These 4-azapteridines experience an addition of the alcohol at C(7), and N(8) underwent an unusual methylation under acidic conditions affording the 7-methoxy-8-methyl-6-phenyldihydropyrazino derivative. Regioselective control by the aldehyde-binding reagent, sodium hydrogen sulfite and sodium sulfite, tends to direct the phenyl group to the C(7). Hinsberg reaction of 5,6-diamino-as-triazines with phenacyl bromide proceeded in regiospecific fashion to give the E-form Schiff bases which then isomerize to the corresponding enamines.