New approach to α-pentafluorosulfanyl-substituted carboxylic acid derivatives via Ireland-Claisen rearrangements

[3,3]-Sigmatropic rearrangement of pentafluorosulfanylacetic acid allyl esters is used as the key step of synthesis of α-pentafluorosulfanylcarboxylic acid derivatives. •New access to α-pentafluorosulfanylcarboxylic acid derivatives is disclosed.•Pentafluorosulfanylacetic acid allyl esters are used as starting materials.•[3,3]-Sigmatropic rearrangement is the key step of the synthesis.•For the first time evidence for the intermediate formation of SF5-substituted ester enolates is observed by NMR spectroscopy. A new synthetic strategy towards α-pentafluorosulfanyl carboxyl compounds was developed. Starting from allylic esters, which were prepared from fluorinated or fluorine free allylic alcohols by esterification with pentafluorosulfanylacetyl chloride, a range of trans-configured γ,δ-unsaturated α-pentafluorosulfanyl carboxylic acids were synthesized via Ireland-Claisen rearrangements. The formation of intermediate (E)- and (Z)-enolates as the key-step was confirmed by NMR spectroscopy, which also indicated that only the (Z)-enolates rearrange, while the (E)-enolates are stable under the reaction conditions and hydrolyze back to the starting allylic esters during aqueous workup. As a consequence an incomplete rearrangement of the starting esters was observed. Transformation of the formed acids into the corresponding methyl esters allowed an easier isolation of the desired pentafluorosulfanyl-containing products.