The reactions of some ortho-naphthoquinones with 2,3-dimethylbutadiene

The reactions of dimethylbutadiene with 1,2-naphthoquinones are shown to involve either addition to the 3,4-double bond [substituents 3-chloro-, 4-cyano-, 3-methoxycarbonyl, 3-nitro-, and 3-methoxy-(partially)] or to the 2-carbonyl group [substituents 4-chloro-, 4-bromo-, 3,4-dichloro-, 3-methoxy-(partially)]. The adduct from 3-chloro-1,2-naphthoquinone is shown to eliminate hydrogen chloride to yield a phenanthrene-9,10-diol, which then undergoes acid-catalysed addition of dimethylbutadiene to yield a hydroxyphenanthrenone.