The Synthesis Of Difluoroalkylated Alkenes And Gem-Difluoroalkenes

Alkenes are a class of hydrocarbons with carbon-carbon double bonds,which have a wide range of applications in organic synthesis and materials.In recent years,as an important class of fluorine-containing blocks in organic synthesis,difluoroalkene structural units can efficiently construct monofluorinated compounds,trifluoromethyl derivatives and fluorine-containing heterocyclic compounds.Therefore,it is of great scientific and social value to develop green,efficient,concise,and atom-economical synthesis method.Depending on whether difluoromethane（CF₂）is directly connected to the alkene bond,it can be divided into difluoroalkyl（-CF₂-）and difluoroenyl（=CF₂）.Combined with the current construction methods of difluoroalkene compounds,the following research is mainly carried out on the green and efficient synthesis of these two structures:1)Visible-light promoted the synthesis of difluoroalkylated alkenes;2)The reaction of trifluoromethylated bromides reduction to form gem-difluoroalkenes.（1）Visible-light promoted the synthesis of difluoroalkylated alkenesIn this chapter,we describe a mild,catalyst-free and simple-handled to use Heck-type reaction study of alkenes and ICF₂COOEt.Mechanism experiments showed that an electron donor-acceptor（EDA）complexes is formed between DMA and fluoroalkyl iodides,which generates fluoroalkyl radicals under the irradiation of purple LEDs,thus achieving this conversion.This photochemical conversion has the advantages of simple operation,high synthesis efficiency,and functional group tolerance,thus providing a simple synthetic path for the synthesis of difluoroalkyl alkenes blocks.（2）The reaction of trifluoromethylated bromides reduction to form gem-difluoroalkenesGem-difluoroalkenes are considered to be the universal precursors of a variety of organofluorines compounds.In addition,this moiety is considered as carbonyl bioisostere with a widespread application in drug,pesticides and life sciences.Here,we use trifluoromethylated alkyl bromides as the substrate to systematically screen and optimize the reaction conditions,and found that the target product can be obtained with excellent yield by using cheap metal zinc powder as a reducing agent,and the yield can still be maintained in the gram scale,which further demonstrates the practicability and reliability of the method.