A novel route to new carbonyl derivatives of cinchonine and cinchonidine

Cinchonine and cinchonidine are readily transformed to their corresponding N-oxides by the action of MMPP in acetonitrile–bicarbonate buffer. Methylation of the N-oxides by iodomethane in dichloromethane leads, under mild conditions, to the formation of a unique enol stabilized by intramolecular hydrogen bonding. In water the enol form tautomerizes to its parent keto derivatives. The reaction has been extended to quinine and quinidine.