Ring-Expansion/Amination Of Cycloalkanones Via Visible Light Photocatalysis

Cycloalkanones are a class of compounds providing a vast pool of C-C bonds in synthetic chemistry.The activation of itsα-C-C bond is one of the most important strategies for the construction of complex C-C bonds and C-X bonds from these chemical feedstocks.To the best of our knowledge,the well-established C-C bonds activation strategies can be generally divided into two catalytic modes,including the precious transition metal catalysis and visible light photocatalysis,which often require the use of directing group or pre-functionalization of the ketone substrates（such as the formation of oxime ester,etc.）.Therein,the atom and step economy of the reaction has aroused more efficient catalytic systems.In this thesis,theα-C-C bond cleavage/amination of cyclobutanones has been achieved under room temperature in the presence of Ru^II photocatalyst.Based on several mechanistic experiments,we propose the ring-expansion/amination process has occurred through the single-electron oxidation of a hydrazone intermediate.We also find it difficult to realize the C-C bonds activation of cyclopentanones or cyclohexanones,which is largely attributed to the low ring-strains inherent in these ketone molecules,and considerable efforts are still devoted to the exploration of more effective conditions.Albeit in the absence of other cyclic ketone substrates,the present ring-expansion/amination of cyclobutanones has proved highly atom economic and up to 56 substrates work well in this catalytic system,featuring a remarkably low catalyst loading and good functional group tolerance.We believe this amination process would undoubtedly find wide applications in the synthesis of aza-cyclic carbon skeleton.