Acid catalysed reactions of 5-formyluracils with enamines. A facile synthesis of 5-acylvinyluracils

Article abstract of DOI:10.1016/S0040-4020(98)00390-1

5-Formyl-1,3-dimethyluracil (1) reacts with secondary amine derived enamines of ketones and aldehydes to provide 5-(acyvinyl)uracil derivatives. The presence of a CH₃ group at C-6 of 1 induces a competitive annulation reaction. Depending on the bulk of substituents 5-(acylvinyl)-uracils acquire cis -diene and E or Z configurations on the vinyl unit. Enamines derived from 1,3-cyclohexanedione and ethyl acetoacetate react with 1 in 1: 2 stoichiometric manner to provide 5-(9-xanthenyl)uracil and 5-(6- cycohexadienyl)uracil (X-ray) derivatives.