The mechanism of the Pechmann condensation is still controversial despite the technological and biochemical importance of coumarins. Here, we present NMR evidence for a mechanism featuring the sequence of initial electrophilic aromatic substitution followed by transesterification and a final dehydration. This mechanism has been convincingly defined and supported by the temporal evolution of two key intermediates which could be purified and identified.

No abstract

Synthesis of 7-Alkoxy-4-trifluoromethylcoumarins via the von Pechmann Reaction Catalyzed by Molecular Iodine. -(DEGROTE, J.; TYNDALL, S.; WONG, K. F.; VANALSTINE-PARRIS*, M.; Tetrahedron Lett. 55 (2014) 49, 6715-6717, http://dx.