Direct comparison of safer or sustainable alternative dipolar aprotic solvents for use in carbon–carbon bond formation

There is a lot of interest in the development of new, safer and more sustainable polar aprotic solvents due to their importance in industrial applications and significant safety issues with the most commonly used examples. One such area of application is in pharmaceutically relevant C–C coupling reactions, where polar aprotic solvents are commonly used for solubility and to stabilise reaction intermediates. Although there are now a number of excellent alternatives in the literature, to date they have not been compared in a single study. This study demonstrates the effectiveness of the green solvents N-butylpyrrolidinone (NBP), γ-valerolactone (GVL), propylene carbonate (PC) and dihydrolevoglucosenone (Cyrene) in Heck and Baylis–Hillman reactions. Good conversions and initial rates were observed in GVL and NBP in Heck reactions. Cyrene exhibited high initial rates of reaction and high yields in the Baylis–Hillman reaction. This demonstrates Cyrene to be a promising alternative polar aprotic solvent for this reaction.