Nitrogen bridgehead compounds. 62. Conformational analysis of 6,7,8,9-tetrahydro-4H-pyrido[1,2-a]pyrimidin-4-ones and their methyl derivatives by NMR spectroscopy
using N,N-diphenylformamide or in a “one-pot” procedure with aniline and triethyl orthoformate. Ethanolysis of 9-N-methyl-N-phenylaminomethylene derivatives 15 and 19 afforded 9-ethoxy-methylene compounds 26 and 27 in the presence of hydrogen chloride. The structures of the 9-substituted 6-methyltetrahydropyridopyrimidin-4-ones 14-25 were elucidated by means of uv, 1H and 13C nmr spectroscopy. 9-Piperidinomethylene