Chromium-Catalyzed Radical Cyclization of Bromo and Chloro Acetals

Cyclopentadienyl chromium β-diketiminate catalysts are used for the radical cyclization of bromo and chloro acetals. Mn powder activated with PbBr2 or PbCl2 is the stoichiometric reductant, and γ-terpinene is the hydrogen atom donor. Although the primary cyclized product can be isolated and structurally characterized as the Cr(III) complex, this substrate can also be reduced catalytically under mild photolysis conditions.