2-Hydroxy-4-oxo-4//-pyrido

The solid state structures of anhydro-(3-methy - and 3-phenyl-2-hydroxy-4-oxo-47/-pyrido[l,2-n]pyridinium)hydroxides, 2-methoxy-3-methyl-47/-and 2-(2-pyridylamino)-47/-pyrido[l, 2-n]pyrimidin-4-ones were established by X-ray diffraction analysis. The amide type N(5)-C(4)-0 bonds are unusually long (144-149 pm) showing no sign of an amide type conjugation. 

Alkylation of mesoionic y ro-(2-hydroxy-4-oxo-47/-pyrido[l,2- ]pyrimidinium)hydroxide with 2-chloromethyl-... 

Methoxy-47/-pyrido[l,2-a]pyrimidin-4-one was prepared from 2-chloro-4Fr-pyrido[l,2-a]pyrimidin-4-one with NaOMe in MeOH for I6h, and from a A7diro-(2-hydroxy-4-oxo-47/-pyrido[l, 2-a]pyridinium)hydroxide with Me2S04 in the presence of NaOMe in MeOH for 3h at room temperature in 93% and 41% yields, respectively (99JCS(P2)1087). 2-(2-Hydroxyethoxy)-47/-pyrido[l,2-a]pyrimidin-4-one was prepared from the... 

Free radical polymerization of anhydro-(2-hydroxy-3-[(3-vinylphenyl)-methyl]-1 -phenyl-4-oxo-47/-pyrido[ 1,2-a]pyrimidinium)hydroxide in DMF at 60 °C for 2 days in the presence of 2,2 -azoizobutyronitrile led to a mesoionic polymer (00MI26). 

IR spectra in conjunction with theoretical calculations (B3LYP/6-31G ) indicate that the (2 /z3 /r6>-(2-hydroxy-4-oxo-4//-pyrido[l,2-(2]pyrimidinium)-hydroxide form exists in solution and in the crystal, but the 2-hydroxy-47/-pyrido[l,2-a]pyrimidin-4-one tautomer dominates in the gas phase (00JCS(P2)2096). 

Vilsmeier-Haack formylation of 2-(4-methyl-l-piperazinyl)-4/7-pyrido-[l,2-a]pyrimidin-4-one with a mixture of POCl3 and DMF at 95°C gave a 3-formyl derivative (93FES1225) while ethyl 4-oxo-6,7,8, 9-tetrahydro-47/-pyrido[l,2-u]pyrimidine-2-acetate at 50 °C yielded a 9-dimethylaminomethylene-3-formyl derivative (01MI4). 3-Formyl-2-hydroxy-8-[2-(4-isopropyl-l,3-thiazol-2-yl)-l-ethenyl]-47/-pyrido[l,2-a]pyri-midin-4-one was obtained from the 3-unsubstituted derivative with oxalyl chloride-DMF reagent in CH2C12 at room temperature for 3h (01MIP1). 

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