Nitrogen Bridgehead Compounds. 62. Conformational Analysis of 6,7,8,9-Tetrahydro-4H-pyridopyrimidin-4-ones and Their Methyl Derivatives by NMR Spectroscopy

Article abstract of DOI:10.1021/jo00353a024

Proton and carbon-13 chemical shift data have been acquired for 2 6,7,8,9-tetrahydro-4H-pyrido<1,2-a>pyrimidin-4-ones and 20 methylated derivatives.Least-squares regression analysis has been undertaken on the aliphatic ring carbons of compounds with unequivocal conformations to determine the methyl substituent parameters for the four distinct aliphatic positions, and the results have been used to estimate the position of equilibrium of confomationally mobil compounds.It is concluded that at room temperature the 6-methyl derivatives predominantly adopt the conformation with a pseudoaxial methyl group and the 7- and 8-methyl derivatives that with an equatorial methyl group, but the 9-methyl derivatives exist in essentially equally populated conformers.Substituent parameters are compared with those previously determined for methylated tetralins.