The Substrate Expansion Of The Novel Oxidation Catalyzed By A Combinative Mn（OAc）₃/CoCl₂System And Its One-pot Application On Pyrrole Synthesis

Mn(OAc)3·2H2O has been well-known for a long time for its powerful, selective, specific and mild reaction abilities as a radical initiator and the methodology on this field has indicated the extensive applications in strategy-level carbon-carbon bond formation during the synthesis of complex molecules. Recently, our group reported a novel oxidative deacetylation and tandem cyclization for hetero Diels-Alder products and furan formation promoted by3equivalent of manganese(Ⅲ) acetate, which could generate the useful bicyclic skeletons in organic synthesis. However, large quantity of the metal salt was not economically and environmentally friendly and an efficient catalyst system was needed for this new oxidative method and its further application.Co(Ⅱ) was one of the most ideal co-metal for Mn(OAc)3since Co(Ⅲ) complex, which was generated by the oxidation of oxygen from air could lead the Mn(II) to Mn(Ⅲ) easily in a reaction system. After the screening on the solvent, co-metal salt species, temperature and time on a basic terpenoid substrate, the optimized conditions were developed successfully for both hetero Diels-Alder and furan pathways.5mol%Mn(OAc)3and2mol%CoC12at60℃for2.5h was the best reaction condition for these two directions while the ethanol was better solvent for hetero Diels-Alder reactions and acetic acid could give more furan product. These two pathways could proceeded well in one molecule with both structural units while the furan was exhibited the priority in competing condition due to the same speed of the deacetyaltion, which made it impossible to form the hetero Diels-Alder products. The mechanism for oxidation involved a consecutive sequence of peroxyl radical insertion, deacetylation, double bond migration and ring formation.The amine compounds in reaction system could be manipulated to produce the heterocycles in the presence of1,4-diketone series, which could be in-situ generated by the oxidative deacetyaltion with Mn(OAc)3/CoC12catalyst system. Following this method, a variety of pyrrole derivatives were synthesized through the one pot reaction in moderate yield.