Nitrogen bridgehead compounds. Part 34. A study of tautomerism in 9-formyltetrahydro-4H-pyrido[1,2-a]pyrimidin-4-ones by 1H, 13C, and 15N nuclear magnetic resonance spectroscopy

Abstract

It has been established (¹H and ¹³C n.m.r.) that for 9-formyltetrahydro-4H-pyrido[1,2-a]pyrimidin-4-ones the tautomeric system imine ⇌ enamine ⇌ enol-imine [(A)⇌(B)⇌(C)] is dominated by form (B) which is stabilized by internal hydrogen bonds. The presence of ca. 15% of (C) in the equilibrium was shown by ¹⁵N n.m.r. While no (A) could be detected.