Cycloallenes. Part 15: 3δ2-1H-Naphthalene (2,3-Didehydro-1,2-dihydronaphthalene) from 3-Bromo-1,2-dihydronaphthalene

As a test as to whether the title intermediate 13 can be liberated from 3-bromo-1,2-dihydronaphthalene (19), the latter was treated with potassium tert-butoxide (KOtBu). Being the major products, naphthalene (20) and 3-tert-butoxy-1,2-dihydronaphthalene (21) provide unambiguous evidence for the intermediacy of 13. When the reaction was carried out in the presence of furan, 2,5-dimethylfuran and spiro[2,4]hepta-4,6-diene, expected (31, 32, 33, 34) and unexpected compounds (30, 35–37) were formed, which either directly resulted from the cycloaddition of 13 or were consecutive products of cycloadducts. Performed in the presence of benzophenone, the generation of 13 gave, inter alia, naphth-2-yldiphenylmethanol (27). This product testifies the intermediacy of the naphth-2-yl anion (24), which emerged from the deprotonation of 13 and was trapped by benzophenone.