The mechanism of cyclisation of 1-ethyl-2-nitrobenzene to give 3-methylanthranil in trifluoromethanesulfonic acid. Evidence for an intramolecular hydrogen transfer

Abstract

Deuterium labelling has been used to show that the cyclisation in trifluoromethanesulfonic acid of 1-ethyl-2-nitrobenzene to 3-methylanthranil does not proceed through an equilibrium concentration of the aci-form of the substrate. Instead, the rate-determining step appears to involve the intramolecular transfer of hydrogen from the α-carbon atom to one of the oxygen atoms of the protonated nitro group. This conclusion is supported by semi-empirical molecular orbital calculations.