Fluorine into Five-Membered Heterocycles

Introduction of Fluorine into Five-Membered Heterocycles 

Introduction of fluorine into heterocyclic systems can be achieved using molecular fluorine. However, direct fluorination is known to be notoriously regio- and stereo-unselective. Extensive work is still going on to overcome these problems (79MI3 86CRV997 89MI1). In special cases 

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A. Introduction of Fluorine into Five-Membered Heterocycles... 

Well-defined substitution patterns in the target molecules can be constructed by a combination of fluorine-free or fluoro-substituted (1,3 ee) components with fluorine-free and fluoro-substituted (1,2 nn) compounds. A representative example for the introduction of fluorine and fluoro-substituted groups into five-membered heterocycles via both educts is the reaction of fluoro-substituted chalcones and pentafluorophenyl hydrazine (88JIC773). 

IV. Introduction of Fluorine, Poiyfluoroaikyl, and Perfluoroalkyl Groups into Five>Membered Heterocycles via Cycloaddition Reactions... 

Introduction of Fluorine-containing Substituents into Five-Membered Heterocycles via Fluoro-substituted 1,3-Dipoles... 

Reactions offluorinated dipoles. In recent years, much effort has been devoted to the preparation of tnfluoromethyl-substituted 1,3-dipoles with the goal of using them to introduce trifluoromethyl groups into five-membered nng heterocycles Fluorinated diazoalkanes were the first such 1,3-dipoles to be prepared and used in synthesis A number of reports of cycloadditions of mono- and bis(tnfluo-romethyl)diazomethane appeared prior to 1972 [9] Other types of fluonne-substi-tuted 1,3-dipoles were virtually unknown until only recently However, largely because of the efforts of Tanaka s group, a broad knowledge of the chemistry of tnfluoromethyl-substituted nitrile oxides, nitnle imines, nitnle ylides, and nitrones has been accumulated recently... 

Five-membered fluorine-containing heterocyclic compounds with two or three sulfur atoms are more extended. A ring expansion reaction of thietanes into 1,2-dithiolanes involving heating with sulfur was used. ... 

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