Abstract
Mass spectra of 4-substituted pyrido [2, 3-d] pyrimidines were examined.
Fragmentations of pyrido [2, 3-d] pyrimidine (I), 4 (3H)-pyrido [2, 3-d] pyrimidinone (VIII), 4-chloropyrido [2, 3-d] pyrimidine (IX) and 4-methoxypyrido [2, 3-d] pyrimidine (X) were analogous to those of corresponding quinazoline derivatives, respectively. Fragmentation of 4-methylpyrido [2, 3-d] pyrimidine (II) afforded (M-·H)+ intermediate written as diazatropylium ion 3' in pathway leading to [M-(·H+CHE≡CH)]+ ion 4. 4-Ethylpyrido [2, 3-d] pyrimidine (III), 4-phenylpyrido [2, 3-d] pyrimidine (V) and 4-phenyl-3, 4-dihydropyrido [2, 3-d] pyrimidine (VI) gave intermediate written as cyclic flagment ion (8, 12, 16) as same as shown in fragmentation of 2-ethylquinoline and 1-ethylisoquinoline. In any way the predominant fragmentation of 4-substituted pyrido [2, 3-d] pyrimidines was proceeded by consecutive loss of cyano radical and hydrogen cyanide accompanied with breakdown or migration of the substituent.
