Reactions of 2-imino-3-aryl-4-phenyl-4-thiazolines with 2-cyanopyrazine and 4-cyanopyridine: difference in reactivity

The kinetics of the reactions of 2-imino-3-aryl-4-phenyl-4-thiazolines (2-ITZ, 3a-e) with 2-cyanopyrazine (2-CPZ, 1) and 4-cyanopyridine (4-CPY, 2) have been carried out in methanol at various temperatures. Results show that 2-ITZ derivatives (3a-e) reacted faster and more readily at ambient temperature with 2-CPZ than with 4-CPY. 2-CPZ readily reacted with methanol forming an amidate ester, while 4-CPY did not. The amidate ester was prone to. nucleophilic substitution (OMe being a good leaving group). Slower reaction rate was observed for the reactions of 2-CPZ with 2-ITZ and its derivatives in THF. On the other hand 4-CPY did not react with 2-ITZ derivatives even under extreme conditions in THF. The order of reactivity of various substituents both in MeOH and in THF is : p-OMe > o-OMe > p-CH3 > o-CH3 > H. The isokinetic temperatures, T-iso for the reactions of 2-ITZ with 2-CPZ and 4-CPY in MeOH were 352.6 K and 438.3 K respectively.