Dihydroquinazolinones by Titanocene-Catalyzed Reductive Radical Addition to Quinazolinones

Here, we describe a novel titanocene-catalyzed synthesis of functionalized dihydroquinazolinones by an intramolecular radical addition to quinazolinones. The mechanistic key-issue is the reduction of the radical σ-complex formed after the addition of the epoxide-derived β-titanoxy radical that is unprecedented in titanocene-catalyzed radical arylations. The diastereoselectivity of product formation is high, and a number of functional groups are tolerated in the pharmaceutically relevant 6- and 7-positions of the dihydroquinazolinone products. If desired, these products can be oxidized to the corresponding quinazolinones with MnO₂.