Lewis Base-Boryl Radicals Enabled The Desulfurizative And Defluorinative Functionalization Reactions

Nitrogen and fluorine-containing compounds have valuable applications in pesticides,pharmaceuticals,dyes,daily chemicals and a variety of functional materials.Therefore,it is of great significance to develop efficient methods to construct these molecules from readily available starting materials.Our group is interested in exploring new transformations of Lewis base-boryl radicals.Under this background,we found that Lewis base-boryl radical could react with thioamides to construct organic amines or nitrogen-containing heterocycles selectively by using different thiol catalysts.We also discovered a boryl radical promoted chemoselectivity-controllable two-stage C-F bond functionalizations of trifluoroacetamides and trifluoroacetates,in which spin-center shift was found to be a key step to enable C-F bond cleavage.The first chapter of my thesis summarizes the methods and strategies of desulfurizative functionalizations of thiocarbonyl compounds and defluorination of trifluoromethyl groups,especially the protocols based on radical transformations.The second chapter of my thesis introduces Lewis base-boryl radicals enabled desulfurizative reduction and annulation of thioamides.The choice of a thiol is crucial to control the chemoselectivity.When PhSH was used as the polarity reversal catalyst,the reduction was preferred to give amines,while the employment of sterically hindered thiol catalyst,such as Ph3CSH,favored the cyclization with an intramolecular alkene moiety that provides N-heterocyclic and carbocyclic skeletons.The Lewis base-borane complexes are readily accessible,bench stable,and nontoxic.This work provides an efficient and practical method for the synthesis of nitrogen-containing compounds.The third chapter of my thesis describes a 4-dimethylaminopyridine-boryl radical promoted sequential C-F bond functionalizations of trifluoromethyl group.Using this strategy,one or two C-F bonds of trifluoroacetic acid derivatives could be cleaved selectively to give di-and monofluoroalkyl radical intermediates,which then undergo either hydrogen atom transfer or radical addition to afford a diverse range of di-and mono-fluorinated products.Mechanistic experiments revealed that the C-F bond was cleaved through spin-center shift process,and the chemoselectivity was controlled by the radical addition step.This method provides an ideal way for the synthesis of monofluoro-or difluoro-compounds from readily available trifluoroacetic acid derivatives.