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■ Nitrogen Bridgehead Compounds. Part 82. An Unexpected Ring Transformation of 6-Hydrozono-4-oxo-6,7,8,9-tetrahydro-4H-pyrido[1,2-a]pyrimidine-3-carboxylates

István Hermecz,* Ágnes Horváth, Tünde Erõs-Takácsy, and Benjamin Podányi

*Chinon Research Centre, Tó u.1-5, Budapest, H-1045, Hungary

Abstract

Treatment of 9-hydrozono-4-oxo-6,7,8,9-tetrahydro-4H-pyrido[1,2-a]pyrimidine-3-carboxylates with the Vilsmeier-Haack reagent gave unsaturated 7-substituted 9-amino-4-oxo-4H-pyrido[1,2-a]pyrimidine-3-carboxylates in a degenerate ring transformation, probably through ring opening via the N(5)-C(6) bond.