Experimental kinetics investigation of stable phosphorus ylides involving a theophylline along with theoretical calculations

In the present work, NMR, theoretical, Kinetics and mechanism investigations were undertaken from a one-pot condensation reaction between theophylline and dialkyl acetylenedicarboxylates in the presence of triphenylphosphine containing novel stable phosphorus ylides 4a-c. Herein, theoretical calculations have been employed for assignment of the most stable isomers (Z or E) of phosphorus ylides 4a,b by natural population analysis, atoms in molecules methods and CHelpG keyword, in which Z-4(a,b) are more stable forms as the majors. The 1H, 13C and 31P NMR data of these ylides are consistent with results obtained from theoretical calculations. In addition, kinetic investigation of new ylides was undertaken by ultraviolet spectrophotometry. Useful information was obtained from studies of the effect of solvent, structure of reactants (different alkyl groups within the dialkyl acetylenedicarboxylates) and also the concentration of reactants on the rate of reactions. Proposed mechanism was confirmed according to the obtained results and steady stat approximation and the first and the third (k3) steps of reaction were recognized as the rate determining and fast steps, respectively on the basis of experimental data.