ACID DEUTERIUM EXCHANGE IN METHOXYQUINOLINES AND THEIR N-OXIDES

Article abstract of DOI:10.1007/BF00519532

Kinetic studies of acid deuterium exchange have been carried out for a series of isomeric 6-, 7- , and 8-methoxyquinolines and their N-oxides, in comparison with the analogous carbocyclic compounds.It has been found that methoxyquinolines are deuterated in the N-protonated form, whereas the N-oxides are reactive in their neutral forms.In full agreement with data for the reactivity of these heterocycles in nitration, quantum chemical calculations show that in exchange in 6-methoxyquinoline and its N-oxide the preferred site for electrophilic attack is the 5-position,and in the 7-isomer the 8-position is preferred.The rate is lower in the 8-isomer, owing to the presence in the latter of intramolecular hydrogen bonding.The probable structure of the transition state in the reaction is discussed.