Metallation reactions. XXV. A re-examination of the metallation reaction of (alkylthio)fluorobenzenes

Article abstract of DOI:10.1016/S0022-1139(99)00097-4

The metallation of (alkylthio)fluorobenzenes by organolithium compounds, lithium amides and butyllithium/potassium tert-butoxide superbasic mixture was re-examined. To avoid the formation of defluorinated compounds all the reactions must be carried out below -80°C. The para-substituted 1a and 1b showed a regiochemistry directed by the halogen; the ortho-derivative 1c underwent metallation ortho to the halogen when treated with lithium tetramethylpiperidide, an α-metallation with butyllithium while sec-butyllithium was less selective. Compounds 1a and 1c allowed the preparation of disubstituted products. At temperatures higher than -80°C increasing amounts of dehalogenated products are formed, whose formation can be explained through the intermediacy of arynes.