Nitrogen bridgehead compounds. Part 73. Ring transformation of nitrogen bridgehead ring systems
Abstract
In an investigation of the role of the substituents in position 3 in the ring-transformation reaction of 6-substituted nitrogen bridgehead condensed pyrimidinones (1) it was revealed that the resonance effect of the substituent in position 3 may play a more significant role than its field contribution. X-Ray crystallographic analysis confirms the structures of pyrido [1,2-a]pyrimidine-3-acetates (7) and (8). While the bicycle of 6-unsubstituted (7) is nearly planar, that of 6-methyl-substituted (8) is twisted around the C(4)–N(5) bond; the consequence of a 1–3 interaction of the substituents in peri positions 4 and 6.