Fructose-catalyzed synthesis of tetrahydrobenzo[b]pyran derivatives: Investigation of kinetics and mechanism

Abstract

Fructose was used as an efficient catalyst for three-component condensation reactions of aryl aldehydes, malononitrile, and dimedone in a mixture of EtOH and H2O as green solvents. The advantages of this method are a short reaction time, high yields, low cost, easy accesses, and simple work-up. The mechanism of the synthesis of a derivative of 4H-tetrahydrobenzo[b]pyran was clarified using spectroscopic kinetic methods. The activation energy (Ea = 65.34 kJ/mol) and related kinetic parameters (ΔG‡ = 69.14 kJ/mol, ΔS‡ = 20.99 J/(mol·K), and ΔH‡ = 62.89 kJ/mol) were calculated, based on the effects of temperature, concentration, and solvent. The first step in the proposed mechanism was identified as the rate-determining step (k1), based on the steady-state approximation.