Fast Ruthenium-Catalysed Allylation of Thiols by Using Allyl Alcohols as Substrates

✍ Scribed by Alexey B. Zaitsev; Helen F. Caldwell; Paul S. Pregosin; Luis F. Veiros

• Publisher: John Wiley and Sons
• Year: 2009
• Tongue: English
• Weight: 382 KB
• Volume: 15
• Category: Article
• ISSN: 0947-6539
• DOI: 10.1002/chem.200900192

✦ Synopsis

Abstract

Green and fast: Allylation of aromatic and aliphatic thiols, by using allyl alcohols as substrates, requires only minutes at ambient temperature with a Ru catalyst (see scheme). Quantitative conversion is normal and the catalyst possesses high functional‐group tolerance.magnified image

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*)(η^3^‐C~3~H~5~)(CH~3~CN)~2~~2~ (2; Cp*=pentamethylcyclopentadienyl) or a combination of Ru(Cp*)(CH~3~CN)~3~ and camphor sulfonic acid. Quantitative conversion is normal and the catalyst possesses high functional‐group tolerance. The use of Ru(Cp*)(CH~3~CN)~3~ 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/l) 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 η^6^‐complexes are not relevant for the catalytic system. Moreover, the DFT results indicate that 1) any η^6^‐complexes from the acids RC~6~H~4~SO~3~H 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, RC~6~H~4~SO~3~^−^ and 3) a sulfonate O‐atom complex will be difficult to detect.