Remote Regiocontrol by a Thioether Group in Diels-Alder Reactions of Naphthazarin: Regioselective Access to Tetracyclic Polyhydroxyquinones

The synthesis of tetracyclic polyhydroxyquinones 5a and 5b was achieved through a sequence involving two Diels-Alder reactions with 1-methoxy-1,3-cyclohexadiene: the first with 2-(p-tolylthio)naphthazarin and the second on the resulting tricyclic derivative previously transformed into a (p-tolylsulfinyl)naphthazarin. The success of this strategy stemmed from the efficient remote regiocontrol exerted by the thioether substituent in the first step.     

Fluorimetric determination of diacetyl and 2,3-pentanedione with isoniazide and a zirconium salt

Diacetyl and 2,3-pentanedione react with isoniazide in acidified solutions to give the corresponding hydrazones which, by reacting with a zirconium (IV) salt, form fluorescent complexes. Both reactions have been studied separately. Variables such as pH, heating time, and excess of reactives are discussed. The method may be used for the determination of these compounds in foods.