| The tandem reaction has a wide range of advantages, including high efficiency,high process economy and atom economy etc. Recently, much attention has been paid to the radical tandem reaction and it becomes one of the hotspots in organic chemistry.The coumarin scaffold is found in many natural products, pharmaceuticals, pesticides,perfumes, dyes, and materials. Traditional synthetic methods usually suffered from the limited sources of raw materials, harsh reaction condition, and high cost of catalyst.Thus, it is of high demand to develop novel and efficient methods for the synthesis of coumarins.In this thesis, we have employed the strategy of radical tandem reaction for the access of coumarin derivatives. The construction of 3-functionalized coumarins involved the radical addition, 5-exo cyclization, and subsequent 1,2-ester migration.1) A silver-catalyzed radical 5-exo cyclization of alkynotes with acyl radical is developed, which affords 3-acyl-4-phenylcoumarinsin excellent yields. The good substrate compatibility under mild conditions is observed. The oxidatively radical5-exocyclization and 1,2-ester migration are involved in this process.2) A metal-free reaction of 1,3-dioneswith alkynotes for the synthesis of3-acetonylcoumarins is described. The presence of tetrabutylammonium bromide and potassium persulfate could facilitate the generation of methene radical from diones.3) A tandem reaction of bromine radical with activated alkynesis realized for the preparation of 3-bromocoumarins through oxidative 5-exo cyclization and 1,2-ester migration. Moreover, The 3-bromocoumarins can be elaborated via transitonal metal-catalyzed phosphation and alkynylation. The method could avoid the use of highly toxic liquid bromine, greatly improving the operational safety for the synthesis of 3-bromocoumarins. |
