The Mass Spectra of Pyrido [2,3-d] pyrimidines

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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+CH≡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 fragment 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.

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