Kinetic Study of the Reaction of 2,4,6-Triphenylpyrylium Ion with Amines. Base-Catalyzed Ring-Opening Reaction of 2H-Pyran Intermediates

Article abstract of DOI:10.1021/jo00174a022

The kinetics of reaction of 2,4,6-triphenylpyrylium ion with butylamine, cyclohexylamine, pyrrolidine, piperidine, and morpholine to yield the corresponding ring-opened divinylogous amides have been studied in methanol at 25 deg C.The reactions with the secondary amines are base-catalyzed, whereas those with the primary amines are not.The results are consistent with the formation of a charged 2H-pyran as a reaction intermediate.With the primary amines the formation of the intermediate is the rate-determining step, whereas for the secondary amines it is the decomposition of the intermediate toward the ring-opened product that is the slow process.In particular, the sensitivity of the base-catalyzed step to the nature of the secondary amine is shown to indicate that the rate-controlling step is the proton transfer from the charged 2H-pyran to the amine to yield the corresponding neutral 2H-pyran.