Kinetics and mechanism of the condensation reaction of symmetrical and unsymmetrical 1,3-diketones with cyanoacetamide in the synthesis of 4,6-disubstituted-3-cyano-2-pyridones

Abstract

The rate constants for the condensation reaction of cyanoacetamide with pentane-2,4-dione, 5-methylhexane-2,4-dione and 5,5-dimethylhexane-2,4-dione catalysed by piperidine were determined under a variety of experimental conditions. A UV spectrophotometric method for rate measurements was developed and the structures of the products were elucidated by means of a spectroscopic study. On the basis of the obtained rate constants, activation parameters and the evidence on the structure of synthesized unsymmetrical 4,6-disubstituted-3-cyano-2-pyridones a possible reaction scheme was suggested. It was thus possible to explain the selectivity of the reaction and the position of substituents in the pyridones obtained.