Rh(III)-Catalyzed Fabrication of [4,3,1]-Bridged Azaheterocycles using Quinone Monoacetals

A rhodium-catalyzed annulation strategy for the fabrication of cyclohexanone-bridged indazolones and other related diazole-ones and diazine-ones was established using quionone monoacetals under mild conditions. On the other hand, the use of 4-hydroxy-4-methylcyclohexa-2,5-dienone under the optimized Rh-conditions produced an <i>ortho-</i>C_Ar-arylated product in moderate reactivity. Mechanistic studies suggested that the coupling proceeded <i>via</i> one-pot C-H activation-Michael/hetero-Michael additions into the enone moiety. Interestingly, the [4,3,1]-bridged-1,2-dihydro-3<i>H</i>-indazol-3-ones underwent unexpected migratory aromatization in acidic condition to produce 3-hydroxy-14<i>H</i>-benzo[<i>c</i>]indazolo[1,2-<i>a</i>]cinnolin-14-ones in high yields.