Allylation with Pummerer-generated Subtituted Vinylthionium Ions

Article abstract of DOI:10.1016/S0040-4020(01)85513-7

Pummerer-derived substituted vinylthionium ions (allyl phenyl sulfoxide, TMSOTf, EtN(i-Pr)2, CH2Cl2, -78 deg C) with a β-trimethylsilylmethyl (2), γ-phenyl (14), or γ-phenylthio (15) group allylate the enol silyl ethers of acetophenone (3) and cyclohexanone (4) in good yield.Allylation with (14) and (15) required slow addition of base in order to limit the rate of production of intermediate, and thus avoid unwanted sila-Pummerer type products.Huenigs's base conjugate addition was not observed in these cases.Both the (E)- and (Z)- forms of allyl sulfoxide (15) were shown to equilibrate to the (E)-transoid conformer prior to allylation resulting in exclusive (E)-vinyl sulfide formation.Blocking of the γ-position resulted in preferential α-attack.