2- -47/-pyrido Vilsmeier-Haack formylation

Vilsmeier-Haack formylation of 2-(4-methyl-l-piperazinyl)-4//-pyrido-[l,2-n]pyrimidin-4-one with a mixture of POCI3 and DMF at 95°C gave a 3-formyl derivative (93FES1225) while ethyl 4-oxo-6,7,8, 9-tetrahydro-4//-pyrido[l,2-n]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]-4//-pyrido[l,2-n]pyri-midin-4-one was obtained from the 3-unsubstituted derivative with oxalyl chloride-DMF reagent in CH2CI2 at room temperature for 3h (OlMIPl). 

Depending upon the reaction conditions, Vilsmeier-Haack formylation of the pyrido [1,2-a] pyrimidines (63 R = H, Me) yielded the 3-formyl derivatives (222 and 223) or the 3-dimethylaminomethylene compounds (224).98,285,296 298 Under vigorous conditions, 2-methoxy-4-oxo-4//-pyrido... 

Depending on the work-up conditions, Vilsmeier-Haack formylation of 4-oxo-6,7,8,9-tetrahydro-4//-pyrido[l,2-a]pyrimidines gave various 9-sub-stituted pyrido[l,2-a]pyrimidines (240 -242).284,319 The 9-aminomethylene derivatives (240) were transformed by hydrolysis in 0.5 N hydrochloric acid to the 9-formyl compounds (241 R3 = H), by ethanolic hydrogen chloride to... 

Vilsmeier-Haack formylation of 9-phenylhydrazonotetrahydropyr-ido[ 1,2-a]pyrimidin-4-ones 636 with a mixture of phosphoryl chloride and dimethylformamide at 60°C for 2 hours, then at 90°C for 0.5 hour, led to the formation of unsaturated dichlorinated 4//-pyrido[l,2-a]pyrimidin-4-ones 331 (91H1455). Because the analog 9-(phenylaminomethylene)tetra-hydropyrido[l,2-a]pyrimidin-4-one 558 (R = COOEt) did not give a similar product, it was assumed that the 6,7-dihydro form 637 was involved in the ring transformation. 

The reaction of 5-acetyl-,V-ethyl-2-(pyrrolidin-l-yl)pyrimidin-4-amine with the Vilsmeier-Haack reagent leads to cyclization followed by formylation in the 6-position of the resulting pyrido[2,3-c/]pyrimidin-5(8/7)-one, thus representing one of the few examples of electrophilic attack at a ring carbon.184-185... 

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