Selective chlorination of hydroxynaphthazarins with dichlorine monoxide. Remarkable stability of some geminal diols derived from 2,3-dihydro-2-oxonaphthazarin

The reaction of 2-hydroxynaphthazarins with dichlorine monoxide in CCl4 aff ords the stable gem-diols 3,3-dichloro-2,3-dihydro-2,2-dihydroxynaphthazari ns in quantitative yields. In the case of 2-hydroxy-3-methylnaphthazarins t he formation of the mixture of corresponding monochlorinated at 3 position 2,3-dihydro-3-methyl-2-oxonaphthazarins and 2,3-dihydro-3-methyl-2,2-dihydr oxynaphthazarins takes place. For these compounds, under certain conditions , the keto - gem-diol equilibrium is observed.