Acid catalyzed coupling of aromatic aldehydes and methyldiazoacetate––a theoretical mechanistic study

The proton catalyzed reaction of methyldiazoacetate and benzaldehyde resulting in the formation of β-ketoesters and 3-hydroxyacrylates has been investigated by means of DFT/B3LYP calculations. Experimentally this reaction is performed using HBF4·Et2O as the catalyst and CH2Cl2 as the solvent. Several mechanistic pathways involving 1,2-migration of phenyl-, H-, and OH-substituents have been considered. In agreement with the experiment, phenyl migration is slightly favored over H- and OH-migrations and thus the formation of 3-hydroxyacrylates over β-ketoesters takes place. Epoxide formation is not feasible in the presence of acid with non-nucleophilic counterions. Moreover, a counterion-assisted pathway has been also taken into account. The overall reaction is similar and competitive to the “BF4−-free” pathway.