Updating the Benzoin Condensation of Benzaldehyde Using Microwave-Assisted Organic Synthesis and N-Heterocyclic Carbene Catalysis

The benzoin condensation of benzaldehyde is a staple of the undergraduate organic chemistry laboratory, introducing the current topic of nucleophilic carbene organocatalysis. Our procedure makes notable improvements to current practice, including the elimination of solvent waste and an "18-fold reduction of reaction time." We have demonstrated that microwave heating provides yields comparable to current practice in 5 min, using significantly less power (70 W) than traditional heating methods. The highest yields were obtained with N,N'-(2,4,6-trimethylphenyl)imidazolium chloride (IMes·HCl) as the catalyst and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) as the base. Our procedure has been successfully executed by multiple cohorts of organic chemistry undergraduates, both with and without pandemic social distancing constraints.