Visible Light-Catalyzed Green Synthesis Of Isatin And Cascade Hydrosilylation/Aminomethylation Of Its Derivatives

Isatin and its derivatives are an important class of heterocyclic compounds and can be used as precursors for pharmaceutical synthesis.Since its discovery,a great deal of research has been carried out on the synthesis,chemical properties,biological activity and industrial applications of isatin.From a historical perspective,the conventional methods for preparing isatin derivatives are the Sandmeyer,Stolle,Gassman,and Martinet procedures.One of the modern trends in the synthesis of isatin is the oxidation of indole and its derivatives,but it is rare to produce isatin gently and efficiently by photocatalytic oxidation of indole and its derivatives.Hydrosilylation refers to the addition reaction which actived by catalysts between a silane compound containing Si-H bonds and an unsaturated compound.Transition metal catalysis has been successfully applied to the hydrogenation or hydrosilylation of compounds containing unsaturated bonds.The hydrosilylation of carbonyl compounds with hydrosilanes results in the formation of corresponding alcohols,but it is more useful to retain silyl groups as protecting groups,as they are valuable synthetic intermediates and monomers used in the production of organosilane polymers and materials.However,the hydrosilylation of isatin has not been reported currently,and it is more challenging to achieve the cascade hydrosilylation and aminomethylation of isatin derivatives with hydrosilane.This paper focuses on the visible light catalyzed green synthesis of isatin and its hydrosilylation/aminomethylation cascade reaction.The specific work includes the following three aspects:(1)We studied 4CzIPN-catalyzed photocatalytic oxidation reaction of indole to construct isatin and its derivatives efficiently.Experiments showed that indole and its derivatives were catalyzed by 4CzIPN to obtain isatin derivatives in moderate to good yields under room temperature conditions and blue light irradiation N-alkyl,N-phenyl and Nbenzyl-substituted indole could obtain corresponding products and the reaction has good functional group tolerance.(2)We studied the reduction of isatin derivatives by hydrosilane with palladium acetate as a catalyst.Except for N-protecting-free isatins,other substrates could obtain corresponding target products in moderate to good yields.To our knowledge,this is the first synthesis of hydrosilation products of isatin and its derivatives.(3)We demonstrated that using palladium acetate as a catalyst for reduction of DMF and isatin derivatives by hydrosilanes,a novel cascade reaction can be realized.With DMF as a reactant and a solvent,the in-situ generated siloxymethylamin intermediate,an adduct of DMF and hydrosilanes,smoothly participates in the successive stages,providing a novel serials of Si,N-functionalized indolin-2-ones in moderate to good yield.This strategy exhibits high chemoselectivity toward carbonyl moieties reduction among the substrates.