The trimethyl ether of fisetin with a free hydroxyl group in 4′-position yields the 5′-aldehyde readily by the action of hexamine. Subsequent oxidation with hydrogen peroxide gives rise to good yields of robinetin trimethyl ether. Its methylenation leads to the synthesis of kanugin and demethylation to the formation of robinetin. This constitutes another example of the two stage ortho-oxidation of the side phenyl nucleus of the flavonols.