Photoredox Catalyzed Cyclopropanation Via "Radical-Polar" Crossover Processes

Cyclopropanes are important structures found in various natural products and biologically active compounds.The reseach on their synthesis has attracted constant attention.Based upon the ongoing evolution of silicates as versatile radical precursors,we introduced the synthesis of cyclopropanes by trapping alkyl radicals with homoallylic（pseudo）halides or bromomethyl radicals with various alkenes.This dissertation is mainly composed of the following two parts:The first part utilizes alkyl silicates as radical sources and puts forward the synthesis of cyclopropanes via the radical-polar reaction of radicals and homoallylic（pseudo）halides.The reaction condition was screened using diisopropyl（4-chlorobut-1-en-2-yl）phosphonite and℃tanyl silicate as the model substrate.And the optimal conditions are as follows:the alkene substrate was stirred under r.t.for 24h with the radiation of a 9 W blue LED with the silicate（2.0 equiv）,the photocatalyst Ir[d F（CF₃）ppy]₂（dtbbpy）PF₆（2 mol%）,and DMSO as the solvent（0.033 M）.The scope of this reaction showed that various radicals derived from silicates performed well in this reaction,and it was possible to introduce substituents on the 3 membered ring by installing groups onto the silicate before carrying out the reaction.From the alkene side,Michael receptors and styrene derivatives all afforded the products in good yields.The radical-polar pathway was confirmed by the successful reaction of substrates utilizing a sulfonate as the leaving group.By teaming different halomethyl radicals with homoallylic halides,we compared the nucleofuge performance of different leaving groups.It turned out that due to the actual surroundings during the reaction,the differences of leaving groups were not in accordance with anticipation.The cascade radical allylation-cyclopropanation reaction was also performed to afford the product with two consecutive radical processes.The competitive experiment revealed that 3-exo-tet cyclization was decisively preferred over 4-exo and 5-exo modes.In the second part the bromomethyl silicate was introduced as a novel methylene transfer reagent.The reaction conditions were:the alkene and potassium[18-Crown-6]bis（catecholato）-bromomethylsilicate（2 equiv）,and the catalyst Ir[d F（CF₃）ppy]₂（dtbbpy）PF₆（2 mol%）,were irradiated with a 9 W blue LED for 24 h dissolved in DMSO（0.033 M）.The scope of Michael receptors and styrenes were broad,affording the cyclopropane products in medium to good yields.This reaction was highlighted by the successful cyclopropanation of unactivated alkenes with medium yields.This showcased the low electronic demand to the alkene substrates of bromomethyl radicals.Compared with the waning yields and the addition product contamination of electron defect substrates with chloromethyl radicals,and the preference of iodomethyl radicals to internal alkenes,bromomethyl radicals showed the broadest substrate scope.In the epilogue,we performed the total synthesis of retinoid X receptor（RXR）agonist LG100268.