An investigation of potential [2,3]-sigmatropic rearrangements of pentafluorophenyl-aza-, -thio-, and -methylene-sulphonium ylides

Abstract

The reactions of pentafluoroaniline and pentafluorothiophenol with dimethyl sulphoxide–trifluoroacetic anhydride at low temperatures followed by triethylamine give the N-trifluoroacetyl compound (6) along with the N-trifluoroacetyl-N-methylthiomethyl compound (7) and decafluorodiphenyl disulphide, respectively; no molecular rearrangements occur. Under similar conditions 2,3,4,5,6-pentafluoro-N-methylaniline gives the cyclohexa-2,5-dienone derivative (8)via hydrolysis of the [2,3]-sigmatropic rearrangement intermediate (9). 2,3,4,5,6-Pentafluorobenzyl bromide and dimethyl sulphide give the sulphonium compound (10) which with butyl-lithium in tetrahydrofuran gives four products derived from the highly reactive [2,3]-rearrangement intermediate (17): (11)(32%), (12)(2.5%), (13)(5%), and (14)(11%). One product only (21)(6%) derived from (17), could be isolated from the reaction in ether. Dimethylsuiphonium methylede reacts with hexafluorobenzene to give a much simpler product consisting of (13)(5%) and (14)(45%).