An Efficient Synthesis of 2,3-Dihydro-1H-pyrimido[1,2-a]quinoxaline 6-Oxides

Abstract

5-Substituted 2,3-dihydro-1H-pyrimido[1,2-a]quinoxaline 6-oxides 1a-f were synthesized by ring closure of N-acyl-N′-(o-nitroaryl)-1,3-propanediamines 2 with ethyl polyphosphate (PPE) or trimethylsilyl polyphosphate (PPSE) to the corresponding 2-substituted 1-(o-nitroaryl)-1,4,5,6-tetrahydropyrimidines 3, followed by spontaneous heterocyclization. The method was extended to the synthesis of the homologous 6-aryl-1,2,3,4-tetrahydro-1,3-diazepino[1,2-a]quinoxaline 7-oxide (1g).

Key words

heterocycles - nitrogen - cyclizations - antibiotics - antitumor agents

References

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5

Due to its aprotic character, PPSE is less prone to promote deacylation reactions and led to better yields than PPE.