Silver-Promoted Free Radical Fluorocyclization With Hypervalent Fluoroiodane Reagent

In recent years,the fluorine-containing organic compounds has been widely used in medicine,pesticides and materials industry with the rapid development of the organic fluorine chemistry.For example,in positron emission tomography(PET),18F-labeled organic compounds are generally used as tracers.The heterocyclic structure is common in natural and synthetic organic molecules,which is also one of the basic structural units in drug design.Considering the significant effect of fluorine atoms on the chemical and biological activities of the drug molecules,it is very meaningful to develop some strategies for the efficient synthesis of fluorine-containing heterocyclic compounds.The electrophilic fluorocyclization reaction is one of the most important means to prepare fluorocyclic compounds.Currently,The commonly used electrophilic fluorination reagents have high-valent nitrogen reagents(such as Selectfluor,NFSI),and high-valent oxygen reagents(such as CF3OF).The drawback of these reagents is that they are very expensive because they are generally made from F2.Hypervalent iodine compounds are mild oxidant,which show similar reactivities to some metals,but more environmentally friendly.A bench-stable cyclic hypervalent iodine(III)fluoro reagent 1-Fluoro-3,3-dimethyl-1,3-dihydro-?3-benzo[d][1,2]iodoxole(compound 1)has aroused the concern of many scholars,for it's convenient preparation from cheap fluoride salt.This feature makes it potentially valuable in the field of radioactive fluorine chemistry.According to the literature survey,we found that the reaction of this compound is normally by an ionic mechanism,and the free radical process has not been reported.Intramolecular fluorocyclization of unsaturated carbamates is described here using compound 1 in the presence of silver catalyst.Both(hetero)aryl-substituted olefins and acrylamides can be utilized as effective substrates.Preliminary mechanistic investigations suggest the reaction proceeds via a cyclization/1,2-(hetero)aryl migration/fluorination cascade involving an unusual radical process.