In the formation of a Grignard reagent from a compound possessing both bromine and chlorine, magnesium preferentially inserts into the C–Br bond over the C–Cl bond. For example, the formation of a Grignard reagent from 1-bromo-2-chloroethane proceeds with good selectivity:
How can this be explained? Can it be rationalised using a reaction mechanism?
- Simon, P. Y.-R.; Oreal, H.; Audran, G.; Schulz, M.; Joly, J.-P.; Siri, D.; Siri, A. Proteasome Inhibiting β-Lactam Prodrugs Useful for the Treatment of Cancer and Neurodegenerative Disorders. World Patent WO 2018/115497 A1, June 28, 2018.