Studies On Molecular Oxygen-Promoted Free Radical Alkylation With Aliphatic Boronic Acid

Oxindoles are the key structural framework for many natural products and biologically active compounds,as well as intermediates for asymmetric synthesis,library design,and drug macromolecular synthesis.In recent years,it is a hot spot for chemists to study the construction of oxindoles all the time.This paper started by the synthesis of oxindoles by free radical alkylation of activated olefins with organoboronic acid,and then extended to other activated olefins such as chromones,coumarins,quinolones and naphthoquinones.First,we summarized the research progress of boronic acid as a free radical precursor.Then we introduced the strategy of oxygen-mediated radical alkylation of activated olefins with organic boronic acid developed by our group in detail.Finally,the research field is summarized and forecasted.The full text is from the following four aspects.The first chapter discussed the research progress of boric acid as a free radical precursor.From the perspective of organic boron chemistry,the free radical reaction of Et₃B/O₂ as a free radical initiator,organoborane as a free radical precursor,potassium trifluoroborate as a free radical precursor and aliphatic boronic acid as a free radical precursor are described in detail.The second chapter described the strategy of oxygen-promoted free radical tandem cyclization of aliphatic boronic acid and acrylamide to synthesis oxindoles.This method utilized only low-cost and easily available oxygen as an initiator of free radicals,and realized tandem cyclization of acrylamide with alkyl radicals in the absence of a metal catalyst and without peroxide.This method is environmentally friendly.The third chapter demonstrated the strategy developed by our group of oxygen-promoted free radical alkylation of aliphatic boric acid with heterocyclic compounds.This method used aliphatic boronic acid as the alkyl donor,which is more stable and safer than other organoboranes to couple with heterocyclic compounds（quinolone,chromone and coumarin,etc.）.This strategy is efficiency.The suitability of functional groups is wide range.We expect this strategy will be widely promoted in the field of organic synthesis.Finally,through the summary of the above two chapters,we outlooked the oxygen-promoted free radical alkylation with organic boronic acid by emphasis on its sustainability and high selectivity.We hope to explore a new and efficient strategy for this field in the future.