Approaches to cyclopropa-fused quinones. The synthesis and photolysis of some 4,9-disubstituted 3,3-dimethyl-3H-benz[f]indazoles

Addition of 2-diazopropane to 1,4-naphthoquinone at low temperature, followed by in situ enolization and acetylation or silylation gave 3,3-dimethyl-1H- benz[f] indazol-4,9-diyl diacetate and 3,3- dimethyl- 9-(t-butyldimethylsilyloxy)-1H- benz[ f] indazol-4-ol, respectively. Functional group manipulation of the latter compound provided a number of other 4,9- disubstituted 3,3- dimethyl- 3H-benz[f] indazoles. Irradiation of the diacetate led to clean extrusion of nitrogen to give the naphtho[b] cycloproparene and an alkene. Attempts to elaborate the cycloproparene into the derived cyclopropanaphthoquinone were unsuccessful. Of the other 4,9- disubstituted 3,3-dimethyl-3H- benz[ f] indazoles examined, only the compound possessing an acetoxy group at C9 was photoactive, and afforded the expected cycloproparene and alkene. Compounds bearing a hydroxy or alkoxy group at C9 were photochemically inert.