Acid-promoted isomerisation of 1-acceptor-1-sulfenyl-substituted 2-vinylcyclopropanes with C1–C2 bond fission and novel 1,5-sulfenyl rearrangement

Abstract

1-Acceptor-1-sulfenyl-substituted vinylcyclopropanes 1 undergo C1–C2 bond fission and 1,5-sulfenyl rearrangement to give 6-sulfenyl-α,β;γ,δ-unsaturated carboxylic esters and nitriles 4 by treatment with acid. The reactions proceed smoothly by use of a sulfonic acid such as p-TsOH·H2O, CF3SO3H etc. in a non-polar solvent. The results, obtained from reactions of compounds 12 and 16, imply that the C1–C2 bond cleavage and deprotonation from the C2-methyl group of substrates 1 occur via a concerted process. The cross-over experiment showed that the 1,5-sulfenyl shift proceeds intermolecularly. Addition of a catalytic amount of m-MeC6H4SH improves the yield of the rearranged product 4c.