Pyrimidines Vilsmeier-Haack reaction

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... 

An interesting variation of this procedure relies upon the formation of malondialdehyde precursors in sita.44-463 Vinylogs of Vilsmeier-Haack intermediates (60),47 formed from dimethylaminoacroleins (59) and phosgene, undergo reaction with 2,4,6-triaminopyrimidine to yield 6-alkyl- and 6-aryl-substituted 2,4-diaminopyrido[2,3-d]-pyrimidines (61). Dimethylaminoacroleins were found to be unsatisfactory.44... 

The Vilsmeier-Haack reagent, prepared from dimethylformamide and phosphoryl chloride, converts 2-amino-5-(4-pyridyl)nicotinonitrile 1-oxide (45) into 7-chloro-6-(4-pyridyl)pyrido-[2,3-c/]pyrimidin-4(3f/)-one (46),72 this reaction also being an example of the conversion of an A-oxide into an st-chloro group. 

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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