Recently, several interesting examples of the photodimerization .of the tropone derivatives have been reported 2,4,5).
Of these examples, the photodimerization of 2-phenoxy-4,5-benzotropone (I) reported by Chapman et al ( ) is noteworthy in that migration of the phenyl group during dimerization was observed. In order to investigate the effect of the condensed benzene ring on the photo-behavior of the troponoid systems and to compare the results with the photodimerization of I, the photochemistry of 2-methyl-4,5-benzotropone (II) was studied.
It was discovered that II, on irradiation, did not afford any of the valence tautomers obtained in the case of the monocyclic troponoids ( ), but gave two kinds of photoproducts including a dimer. The result will be reported here.
(1)
When a solution of I in acetonitrile was irradiated externally in Pyrex vessel, under nitrogen atmosphere using high pressure mercury lamp (Toshiba H400-p), two products, III, m.p. 267", and IV, m.p. 704-6", were obtained in 2-7 and o-10 $ yield accompanied with a large amount of polymer. The yields of III *and IV were practically unchanged, if benzene, acetone and isopropyl alcohol were used as the solvent.
Elemental analysis and molecular weight determination by mass spectroscopy (Table ) show that IV is a dimer, C24H2002 and III is a dehydrogenated