Nitrogen bridgehead compounds. Part 4. 1→3 N→C-acyl migration. Part 2

Abstract
Ring closure of 2-substituted 3-(2-pyridylamino)acrylates (1) in phosphoryl chloride–polyphosphoric acid gives pyrido[1,2-a]pyrimidines (2), whereas (6-substituted 2-pyridyl) derivatives in Dowtherm A afford pyrido[1,2-a]-pyrimidines (2) and 1,8-naphthyridines (3). The 6-substituted pyrido[1,2-a]pyrimidines (2) can be converted thermally into 1,8-naphthyridines (3) by 1 → 3 NC-acyl migration. Similar acyl migrations can be observed in other such systems.

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