Unequivocal total assignment of 13C and 1H NMR spectra of some pyrido[1,2-a]pyrimidine derivatives by 2D-NMR

We report the total assignments of the 13C and 1H NMR spectra of some 4‐methyl‐2‐oxo‐(2H)‐pyrido[1,2‐a]pyrimidine and 2‐methyl‐4‐oxo‐(4H)‐pyrido[1,2‐a]pyrimidine derivatives. The products were characterized by 1H and 13C NMR and reported data for similar compounds. No comparative data for the two sets of isomeric compounds with respect to 13C and 1H NMR have been reported to date. We made some detailed studies of the 2D NMR spectra of these compounds and observed that assignments made for non‐protonated carbon atoms by us and those reported in the literature for similar compounds need correction. The revised assignments were made on the basis of heteronuclear single quantum correlation (HSQC) and heteronuclear multiple bond correlation (HMBC) techniques. Copyright © 2003 John Wiley & Sons, Ltd.