Rapid access to the core skeleton of the [3 + 2]-type dimeric pyrrole–imidazole alkaloids by triplet ketone-mediated C–H functionalization

The ability of triplet ketones to abstract a hydrogen atom from hydrocarbons is reminiscent of that of the high-spin metal-oxo complexes in C–H oxidation enzymes. In practice, the reactivity of triplet ketones is easier to control and applicable to promoting a wider range of reactions. We demonstrate herein the synthetic utility of triplet ketone-mediated C-addition of methanol to cyclopentenone derivatives with an expedient synthesis of the core skeleton of the 3 + 2]-type dimeric pyrrole–imidazole alkaloids. Remarkably, this photochemical C–H functionalization reaction is highly regioselective and can tolerate a good range of functional groups.