Palladium-Catalyzed[7+2] Dipolar Cycloadditions With Photochemcially Generated Ketenes

Medium-sized rings are not only widely found in natural products,but also important structural units of many functional molecules including medicines and pesticides.Therefore,the development of efficient synthetic methods to access these compounds has been an important task of synthetic community.However,the unfavorable enthalpic and entropic effect together with transannular interactions make the synthesis of medium-sized rings,especially for nine-membered rings,more difficult.In address this challenge,in this thesis photochemcially generated ketenes were used to achieve the efficient synthesis of two types of nine-membered lactones through the[7+2]dipolar cycloaddition reaction.The details are as follows:In the first work,pyrazolone derivatives were used as 1,7 dipoles,ketene photogenerated in-situ by Wolff rearrangement of α-diazoketones were used as a class of reactive C2 synthons.[7+2]cycloaddition using synergistic palladium catalysis and visible light activation,obtaining nine-membered lactones in 29%-94%yields.After that,we try to probe an asymmetric variant.The asymmetric nine-membered lactones can be obtained with 38%ee value as the best results.In the second work,spirovinylcyclopropyl oxindole were used as 1,7 dipoles under the palladium catalysis,ketene photogenerated in-situ by Wolff rearrangement ofα-diazoketones were used as a class of reactive C2 synthons.[7+2]cycloaddition using synergistic palladium catalysis and visible light activation,the nine-membered ring lactones can be obtained in 43%-87%yields in 14 examples.Also,the asymmetric products can be obtained in 40%enantioselectivity when using the P,S ligand.