Annulation Reactions And Dehydrogenation Coup Ling Reactions Via Electrochemical Aryl C-H Functionalization

Aryl C-H functionalization is one of the most economical and efficient synthetic strategies for the construction of aryl carbon-carbon/heteroatom bond,which avoids the pre-functionalization of the substrates in high atom-and step-economy manner.Conventional aryl C-H functionalization are typically carried out at high temperatures and rely on use of expensive transition-metal catalysts and stoichiometric oxidants.In recent years,electrochemistry has been recognized as a promising green synthesis technology to replace traditional stoichiometric oxidants and reductant s.Implementation of accurate pointing by controlling the reaction potential,some side reactions can be avoided,and the reaction selectivity and conversion efficiency are improved.Based on the advantages of organic electrosynthesis,electrochemical techniques can effectively solve the lack of conventional aryl C-H functionalization,and have a major study significance for the development of aryl C-H functionalization.This paper mainly focuses on the electrochemical annulation reactions and dehydrogenation coupling reactions via aryl C-H functionalization.The main research contents include the following aspects:(1)Recent progress in the electrochemical annulation reactions and cross dehydrogenation coupling via aromatic C-H functionalization are reviewed,which mainly focused on summary of both transition-metal-catalyzed and transition-metal-free aromatic C-H functionalization transformations.Moreover,The results and mechanisms of these reactions are also descibled and discussed.(2)We have developed a Ru(?)-catalyzed electrooxidative[4+2]annulation of benzylic alcohols with internal alkynes via aryl C-H functionalization for the synthesis of multi-substituted isocoumarins,wherein benzylic alcohols act as the weakly directing group precursors to promote the aryl C-H functionalization.The reaction features broad substrates scope,excellent tolerance of a wide range of functional groups,and practical incorporation of the isocoumar in unit into important bioactive molecules.The control experiments and cyclic voltammetry analysis suggested that the annulation reaction is achieved via the generation of the active benzoyloxy-Ru(?)intermediates by oxidation of benzylic alcohols using an electrooxidative Ru(?)catalysis,not via the direct formation of acid intermediates,which oxidized from alcohol.(3)An electrochemical decarboxylative[4+2]annulation between aryl?-keto acids and internal alkynes using an aryl C-H functionalization strategy for the preparation of 1H-isochromen-1-ones is described.By utilizing cooperative anode and ruthenium catalysis,the reaction enables the formation of several new bonds in a single reaction step avoiding use of additional external oxidizing reagents.Isotope labeling experiments showed that H₂O serves as the carboxyl oxygen atom source of the target products,not oxygen.In addition,the decarboxylation process prior to the C-H functionalization for the generation of C(sp²)-Ru species.(4)A metal-free electrochemical[3+2]heteroannulation between N-Ts-aniline and electro-deficient pyridines by dual aryl C-H aminations,allowing access to highly valuable pyrido[1,2-a]benzimidazole derivatives under mild conditions in a undivided cell was developed.By simply tuning the conditions to alkaline,6-aminopyrido[1,2-a]benzimidazole derivatives can be constructed with high selectivity.The resulting product IV-10aa exhibited strong fluorescence at different concentrations,with a large Stokes shift,and the fluorescence inhibition was obvious in the presence of Co²⁺.Cyclic voltammetry analysis and control experiments indicated the annulation process involves radical/radical cross-coupling.(5)An ortho/para-selective C(sp²)-H/C(sp²)-H electrochemical cross dehydrogenation coupling of 2-naphthylamine and aniline in the absence of metal catalysis for the construction of a series of unsymmetrical biar ys with excellent selectivity was established.Some bioactive drug structures were successfully introduced into biarys compounds by electrochemical technology.It is worth noting that the choice of the high dielectric constant fluorine-containing solvent HFIP is the key to achieving high-efficiency biaryls conversion,because HFIP has a significant stabilizing effect on radical cations.