Oxidation of bisnaphthols to spironaphthalenones, revisited

Bis(2-hydroxy-1-naphthyl)methane derivatives have been efficiently convened to their corresponding spirans through three methods, i.e. oxidation by TCCA under mild reaction conditions, Ph3Bi catalyzed air oxidation, and by electrochemical reaction. The first two methods are diastereoselective and give either of the two possible diastereomers, while the electrochemical method produces equal amounts of these diastereomers.