Studies On The Ring-Opening Reaction Of In Situ Generated Siloxy Gem-Difluorocyclopropanes

The introduction of fluorine or fluorinated moieties into organic molecules can remarkably enhanced their lipophilicity,metabolic stability and the acidity or basicity of proximal functional groups.Therefore,the fluorinated organic compounds have irreplaceable physical,chemical and biological properties in the fields of agrochemical,medicine and materials.Nowadays,only 13 kinds of organic fluorides have been found in the nature.So,it has been a research focus on designing and synthesizing more excellent fluorine-containing skeletons for the application in the life science and material science.In the past,the simple,economical and efficient synthesis methods access gem-difluorocyclopropanes have been well-established.Recently,it has been gradually paid attention that gem-difluorocyclopropanes as fluorine-containing three-carbon synthons constructing various fluorinated organic molecules by their ring-opening reactions.This work thoroughly studied the ring-opening reactions of siloxy gem-difluorocyclopropanes,including the following five chapters:In chapter one,introducing different functional groups into gem-difluorocyclopropane can change their structure and chemical reactivities in different degrees.According to the difference of functional group connected in gem-difluorocyclopropane’s structure,we classified and summarized the ring-opening reactions of gem-difluorocyclopropanes in recent years.In chapter two,we realized a unique domino reaction of enolizable carbonyl compounds with TMSCF₂Br under only a catalytic amount of n-Bu₄NBr as initiator for the construction ofα-fluoroenones.In this tandem reaction,TMSCF₂Br acts as not only the difluorocarbene source but also the TMS transfer agent as well as internal bromide and fluoride anion catalyst.In chapter three,a highly controlled ring opening of siloxydifluorocyclopropanes,formed by n-BuN₄Br-catalyzed difluorocyclopropanation ofα-acyl ketene dithioacetals by using TMSCF₂Br as a unique difluorocarbene source,results in copper difluorohomoenolates with assistance of copper followed by an intramolecular addition and elimination reaction leading toα,α-difluorocyclopentenones efficiently.The strategy can be extended to the transformation of vinylogous thioesters.For the first time,we developed siloxydifluorocyclopropanes into difluorohomoenolate equivalents,which was used in the synthesis of fluorinated organic functional molecules.In chapter four,a method for the halogenation of siloxydifluorocyclopropanes was realized simply and effectively,and a series ofα,α-difluoro-β-halo-substituted ketones were synthesized.In chapter five,we explored a tandem Ag-catalyzed defluorination ring-opening diarylation reaction of siloxydifluorocyclopropanes for the synthesis of polysubstituted2-fluoroallylic compounds.This multicomponent reaction proceeds smoothly in good stereoselectivity,which is due to a stereoselective addition of arenes toα-fluoroketones by using Ag（I）as chelating catalyst.Alkenes proved to be extended to the catalytic system.