1H, 2H, and 11B NMR spectroscopy has been used to study the mechanism of the Fries rearrangement of
aryl formates promoted by boron trichloride by monitoring both the substrate and the Lewis acid. DFT
calculations were employed to investigate the energetics of several reaction paths and to calculate NMR
chemical shifts of key intermediates and products. After the formation of a 1:1 substrate−Lewis acid
adduct, the rearrangement proceeds in two steps, beginning with the cleavage of the ester bond and the
release of formyl chloride in situ, which, in turn, acts as a formylating agent, introducing an aldehydic
functionality into the aromatic ring. The high regioselectivity (only the ortho product is obtained) is also
accounted for by the proposed intermolecular, Lewis acid-assisted mechanism.
The Fries rearrangement of model aryl formate esters, promoted by boron trichloride, has been investigated by means of NMR spectroscopy (both experimental and computational) and by DFT calculations. Firstly, the 11B NMR chemical shifts of a series of model boron compounds have been predicted by GIAO-B3LYP/6-31G(d,p) calculations, in order to make predictions of the chemical shifts of transient reaction intermediates observable by 11B NMR. Such 11B spectra for the reaction of two esters (phenyl and 3-methyoxyphenyl formates) have been obtained, and are found to follow different patterns which can be rationalized on the basis of computed chemical shifts. Secondly, DFT calculations (B3LYP/6-31G(d,p) level) have been employed to investigate several mechanistic pathways of the rearrangement of phenyl formate. It is found that the pathways leading to the lowest activation energies are those in which formyl chloride is generated from a complex between phenyl formate and BCl3, which then acts as the formylating agent.
Orthoamides of six alkynecarboxylic acids, possessing reactive substituents in 3-position, are transformed by elemental iodine to the corresponding vinylogous guanidinium iodides. The constitution of two of the iodides was established by crystalstructure analysis.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.