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The dimerization reactions of 2-bromo-3,5,6-trimethyl-1,4-benzoquinone have been examined. 2,2′-Dimeric benzoquinone was prepared via a Stille-type homocoupling, whereas an oxepin was formed by the treatment of the title quinone with hexamethylditin, CuI, and (±)-BINAP in DMF. Two dimerization reactions involving a hetero Diels–Alder reaction between quinones and quinone methides were also observed.

A 2H-naphtho[1,2-b]pyran, prepared by dimerization of 2-bromo-3-methyl-1,4-naphthoquinone and O-methylation, readily undergoes solid-state [2 + 2] photodimerization to give a photodimer in excellent yield and with excellent selectivity. Retro [2 + 2] cycloaddition can be achieved by irradiation of a solution of the photodimer in chloroform. Interestingly, the 2H-naphtho[1,2-b]pyran dimerizes with a skeletal rearrangement to afford 2,5-dihydro-1-benzoxepin dimers upon irradiation in methanol or via irradiation with hexamethylditin. Furthermore, treatment of the resulting dimers with triethylamine regenerates the 2H-naphtho[1,2-b]pyran monomer. Significant differences in the color, fluorescence, and cytotoxic properties of the monomer and dimers were observed.