3- fluoro-5-methylthiophene

Fluorothiophene and 2-fluoro-5-methylthiophene were prepared by the exothermic reaction of perchloryl fluoride with the corresponding organolithium heterocyclic compounds in anhydrous ether. 

A number of cycloalkyl-, vinyl-, aryl-, and benzyllithium compounds (predominantly benzyl-lithiums) are converted into fluoro derivatives in good to excellent yields, e.g. formation of 4, 5, and 6 19 however, when this method was applied to the synthesisof 3-fluorobenzocyclobutene from the lithium salt a violent explosion occurred when the reaction mixture was warmed from — 70 C to room temperature.20 Various fluoro-substituted thiophenes 7 are obtained when the starting compounds (thiophene, 2-methylthiophene, etc.) arc transformed with al-kyllithium compounds to the corresponding lithium derivatives then fluorinated with perchloryl fluoride at 0 C.21 Potassium tricyanomethanidc is converted at —15 C in triglyme into tricyanofluoromethane in 81 % yield.22... 

Electron-withdrawing and electron-donating groups on the pyridine moiety were compatible. It is worth noting that ster-ics and electronics play an inportant role in governing C2- vs. C6-selectivity for C3-substituted pyridines sterically hindered substrates, such as C3-pivalamido, phenyl, and ester substrates, preferred C6-arylation, whereas, due to electronic effects, C3-chloro- and fluoro-substrates favored C2-arylation. Other azines could also be cross-coupled with 2-methylthiophene including pyrimidine, quinoline, quinoxaline, pyridine, and pytidazine. 

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