Photoredox Asymmetriccatalyticof 3-chlorooxindoles Toformaquaternarycarbonchir Alcenter

Oxindoles are intermediates for the syntheses of many natural products,and are widely used in various areas such as medicines,pesticides,and materials due to their remarkable physiological and pharmacological activities.The enantiomers of oxindoles with chiral centers tend to exhibit different physiological activities,the synthesis of a single enantioselective compound is thus of great significance.One of the important approaches to obtain enantioselective compounds is the induction by using a chiral catalyst.Meanwhile,with the concept of “green chemistry” being constantly raised,solar energy has been recognized by the majority of people as a non-polluting,cheap,readily available and renewable green energy source.The rational utilization of solar energy to convert into chemical energy has become one of the biggest challenges of the new century.The visible light-induced chemical reaction can effectively convert solar energy into chemical energy,it has drawn more and more attention due to its high efficiency,environmental friendliness,mild reaction conditions,and easy operation.The dual catalytic mode combining the above asymmetric catalysis with visible light catalysis is expected to have advantages in both areas,thereby obtaining highly enantioselective compounds.Based on the dual catalytic mode,this thesis has carried out the following study:Firstly,the dual catalytic mode combining asymmetric catalysis with visible light catalysis is briefly introduced.According to the reaction mechanism,free radicals are generated by photoredox,and the chirality is controlled by asymmetric catalysis.Compared with the conventional asymmetric catalytic method for constructing all-carbon stereocenter compounds,the dual catalytic mode has milder reaction conditions and facile operation,and the chiral center is easy to control.At the same time,the problem of excessive steric hindrance in the synthesis of all-carbon stereocenters is largely overcome.Secondly,a series of 3-haloxindoles containing different protecting groups were designed and synthesized.They were reacted with N-arylphenylglycine groups catalyzed by a photoredox catalyst dicyanopyrazine-derived chromophore(DPZ)and achiral phosphoric acid.The sulfonyl protected 3-chloroxindoles exhibited the best regioselectivity and enantioselectivity.The sulfonyl protected oxindoles changed the electron cloud density at the 3-position and thus generating more electron-deficient radicals.As a result,cross-coupling between these radicals and the electron-rich radical generated by N-arylphenylglycine was easier to occur.Finally,by employing a dual catalytic mode of DPZ as a photoredox catalyst and combining with chiral phosphoric acids,the sulfonyl protected 3-chloroxindoles and N-arylphenylglycine were used as substrates,and by changing the reaction solvents,temperature,additives under anaerobic visible light conditions,all-carbon stereocenter compounds with high enantioselectivity and high yield were obtained.Moreover,Horsfiline or natural and non-natural bioactive molecules with high enantioselectivity could also be achieved.