Depending on the substituents at C(3) and on the reaction conditions, Vilsmeier - Haack formylation (POCl3 - DMF) of 6,7,8,9-tetrahydro-4H- pyrido[1,2-a]pyrimidin-4-ones (I) led to 9-(dimethylamino-methylene)- or 9-(ethoxymethylene)-6,7,8,9-tetrahydro-4H-pyrido[1,2-a]pyrimidines (II) and (IV), respectively, or 9-formyl-1,6,7,8-tetrahydro-4H-pyrido[1,2-a]pyrimidines (III). Compounds (II) may be converted into (III) or (IV). Owing to the enhanced activity of their 9-CH2 group, the 3-carboxylic acid derivatives of (I) form compounds (II) even on the action of dimethylformamide diethyl acetal, and compounds (IV) on the action of triethyl orthoformate in Ac2O. Compounds (III) may be converted back into (I) by hydrolysing the 9-formyl group. Their spectral data show that compounds (II) and (IV) exist exclusively in the E-configuration, and compounds (III) predominantly in the 1,6,7,8-tetrahydro-tautomeric form.
|Number of pages||9|
|Journal||Journal of the Chemical Society, Perkin Transactions 1|
|Publication status||Published - Dec 1 1983|
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