Visible-Light Photocatalytic Organic Synthesis Using Hydrazine And Olefine Derivatives

Visible light photoredox catalysis(VLPC)has emerged as a powerful tool in synthetic organic chemistry,owing to its natural abundance,ease of use,and fascinating potential of applications.It has already found major applications in enantioselectiveα-functionalization of carbonyl compounds,[2+2] cycloadditions,dehalogenationreactions,decarboxylative couplings,radical C–H functionalization of aromatic compounds,as well as the synergistic catalysis involving VLPC for oxidative couplings/annulations.In this paper,through the study of catalysts and reaction conditions,we have developed high efficient green protocols for the synthesis of pyrazoles,alkenes and hydrazones usingvisible light photocatalysis,including:Part Ⅰ: In the first part of the paper,we have developed a green and high yielding synthesis of polysubstitutedpyrazoles through a VLPC-promoted reaction of hydrazine with Michael acceptors.The reaction is proposed to go through VLPC-promoted oxidation of hydrazine to diazene followed by its addition to Michael acceptors,other than the conventional condensation of hydrazine with a carbonyl.The synthesis conditions of the synthesis method are very mild and have the advantages of easy availability of raw materials and high yield.This method opens up a new field for pyrazole synthesis.Part Ⅱ: In the second part of the paper,we have developed a metal-free protocol for the conversion of alkenes to ketones through oxidative radical addition with arylhydrazines.The reaction is easy to operate,green economy and environmental protection,have high universality,low reactivity,and its by-product only have nitrogen and water.Synthetically,this system could be scaled up to 20 mmol with good efficiency.Part Ⅲ:In the third part of the paper,we have developed a metal-free protocol for the synthesis of hydrazones through visible light mediated oxidative cleavage of C=C bonds to directly construct C=N bonds.Instead of metal salts and organic peroxides,molecular oxygen is used as the terminal oxidant for the reaction of alkenes andhydrazines.It showsbroad substrate scope with respect to both alkenes and hydrazines,and a variety of hydrazones were synthesized in moderate to good yield.Preliminary mechanistic studies suggested a diazetidine intermediate for the reaction.