Pyrido pyrimidinones, -diones

Electrophilic substitution at ring nitrogen atoms has been limited to protonation and iV-alkylation of the anion derived from a pyrido-pyrimidinone.i - Thus, the sodium salt of pyrido-[2,3-d]pyrimidine-2,4-(l//,3ir)-dione and dimethylsulfate yield the 1,3-dimethy] derivative (176). 

A 1,4-dipolar cycloaddition between tetrahydropyrido[l,2-a]pyrimidi-none 114 (R = Me) and 4-methyl-l, 2,4-triazoline-3,5-dione 666gave stable adduct 667 in acetonitrile or in acetic acid at room temperature for 1 hour (Scheme 44) (85CB4567). When ethyl cyanoformate was used as dienophile in boiling toluene for 20 hours, ethyl 3-methyl-4-oxo-6,7,8,9-tetrahydro-4//-pyrido[ 1,2-a]pyrimidine-2-carboxylate 669 was obtained (86CB1445). Pyrido[l,2-a]pyrimidine-2-carboxylate 669 was formed from the initial adduct 668 by elimination of phenyl isocyanate. Reaction of tetrahydropyr-ido[l,2-a]pyrimidinone 114 (R = Me) with l-(diethylamino)-l-propyne in... 

The typical ring positions available for the introduction of carbofunctional groups by exchange of hydrogen are the various -CONH— functions of pyrido[2,3-t/]pyrimidinones.87 265 322 324 For alkylation or acylation reactions of pyrido[2,3-cf]pyrimidine-2,4(l//,3//)-diones 4, in most cases the NH groups are converted into the respective anions by sodium hydride78 322 or sodium ethoxide.323 Mannich reactions with formaldehyde/piperazines have been reported,323 as has been the introduction of propynyl groups under Mitsunobu conditions.324... 

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