Photochemical Generation and Reversible Cycloaromatization of a Nine-Membered Ring Cyclic Enediyne.
Irradn. of the nine-membered ring enediyne precursor, which has one of its triple bonds masked as cyclopropenone, efficiently (Φ = 0.34) generates the reactive 4,5-benzocyclonona-2,6-diynol. The latter rapidly equilibrates with the corresponding 1,4-didehydronaphthalene diradical and then undergoes rate-limiting hydrogen abstraction to produce the ultimate product of the Bergman cyclization, benz[f]indanol. [on SciFinder(R)]