Pyrimidinones tetrahydropyrido

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 mass spectrometric behavior of the isomeric 2-oxo-2H- and 4-oxo-4 -6,7,8,9-tetrahydropyrido[l,2-<3]pyrimidines was studied under electron-impact induced polarization (97RCM664). The molecular ion of the 2-OXO-2H isomer appeared to be much more stable than that of the 4-oxo-4 isomer. The fragmentation of the molecular ion (M+) of the 4-oxo-4 isomer is related mostly to the saturated piperidine ring, whereas that of the 2-oxo-2H isomer is much more selective, the only significant process is the primary loss of a CO molecule from the pyrimidinone ring via contraction of the ring. Electrospray ionization quadrupole ion-trap mass spectrometric characterization of risperidon (11) was presented and a possible mechanism for the observed fragmentation pattern was... 

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