Fast ruthenium-catalysed allylation of thiols by using allyl alcohols as substrates

Article abstract of DOI:10.1002/chem.200900192

The allylation of aromatic and aliphatic thiols, by using allyl alcohols as substrates, requires only minutes at ambient temperature with either a Ru ^Iv catalyst, [Ru(Cp*)(n³CH₅)(CH ₃CN)₂](PF₆)₂ (2; Cp* = pentamethylcyclopentadienyl) or a combination of [Ru(Cp*)(CH ₃CN)₃](PF₆) and camphor sulfonic acid. Quantitative conversion is normal and the catalyst possesses high functional-group tolerance. The use of [Ru(Cp*)(CH₃CN) ₃](PF₆) alone affords poor results. A comparison is made to the results from catalytic runs based on the use of carbonates rather than alcohols, by using 2 as the catalyst, and it is shown that the products from the alcohols are formed faster, so there is no advantage in using a carbonate substrate. The observed branched-to-linear (b/1) ratios when using substituted alcohols decrease with time suggesting that the catalysts isomerise the products. A new methodology from which one can select the desired isomeric product is proposed. DFT calculations and NMR spectroscopic measurements, by using an arene sulfonic acid as co-catalyst, suggest that ⁶-complexes are not relevant for the catalytic system. Moreover, the DFT results indicate that l)any rf-complexes from the acids RC₆H₄SO ₃H result from deprotonation of the acid, 2) complexation of the thiol, via the deprotonated sulfur atom, is preferred over complexation of the O atom of the sulfonate, RC₆H₄SO₃and 3) a sulfonate O-atom complex will be difficult to detect.