Efficient Thiolation of Alcohols Catalyzed by Long Chained Acid‐Functionalized Ionic Liquids under Mild Conditions

Abstract

Thioethers as important building blocks have been usually found in organic synthesis. Herein, a series of long chained acid‐functionalized ionic liquids derived from pyrrolidine were applied for the thiolation of alcohols to synthesize different compounds containing thioether structures. This kind of ionic liquids exhibited higher efficiency than general ionic liquids based on imidazole, providing up to 99 % yield with [BsCtP][OTf] as the catalyst at room temperature for 0.25 h. The results indicated that the activities of the ionic liquids have relationship with the side chain length of ionic liquids based on pyrrolidine, anions and cations. The catalytic system had wide substrate scope and was applicable for the reaction of aromatic primary and secondary alcohols and thiols including aliphatic and aromatic thiols, benzothiazole‐2‐thiols and benzooxazole‐2‐thiols. Besides, there was no obvious change in activity of the catalyst after six runs. Thus, the catalytic system exhibited good recyclability. Additionally, carbocations should be the key intermediate and several functionalized groups of the ionic liquids have synergetic effect for the thiolation.

Ionic Liquids with Multi‐Active Sites Synergistically Catalyzed Metal‐Free Transformation of Alcohols Using Dimethyl Carbonate as an Environmental Solvent

“…According to our results and the previous report, [24–28,44] we proposed a possible mechanism involving carbocation and ethers as the intermediates and synergistically promoted effect of hydrogen bonding (Scheme 6). Initially, we thought that the activities may be significantly influenced by the acidities of the ionic liquids.…”

“…And carbocation was usually recognized as the key intermediate derived from alcohols especially in Lewis or Brønsted acid‐catalyzed systems among the third developed systems. Previously, we have developed several efficient and mild systems catalyzed by acidic ionic liquids to generate carbocations from alcohols, which can react with sulfonamide, amide, carbamate, aromatic amine, olefins, thiols et al to produce corresponding products [24–28] . Ionic liquids exhibit high thermal and chemical stability, negligible vapor pressure, easy recyclability, tunable properties and could be used as environmental catalysts for the reaction by introducing different functionalized groups [29–33] .…”

“…As a continuation of our efforts to develop reactions involving generated carbocation as the intermediate, [24–28] we wanted to exploit more efficient, mild and environmental system to catalyze the atom economic C3 substitution of 4‐hydroxycoumarins with carbocations derived from alcohols. The reaction was synergistically catalyzed by metal‐free pyridine‐based ionic liquids with multiple active sites using DMC as the green solvent, providing up to 99 % yield (Scheme 1 and Figure 1).…”

Direct deoxygenation of active allylic alcohols via metal-free catalysis

“…53–56 Alcohols, especially highly active allylic alcohols, under the action of Brønsted acids easily form carbocations, 57 which is also typically considered to be the intermediate step in Lewis acid-catalyzed direct deoxygenation. 58–60 Continuing our research on the transformation of alcohols using specific acidic materials, 61–64 we believe that Brønsted acids can provide protons to activate the hydroxyl group of highly active allylic alcohols in order to break the C–O bond and generate carbocations. Meanwhile, benzyl alcohol can provide the hydrogen source that acts as the reductant for a series of reactions, 65–68 except hydrosilanes, hydrazine, Hantzsch ester, HCOOH, H 3 PO 3 , and so on.…”

Embedded ionic liquid modified ZIF-8 in CaMgAl hydrotalcites for bio-glycerol transesterification

“…Ionic liquids as green catalysts can be designed and synthesized according to service conditions. 12–14 The use of basic ionic liquids in transesterification is conducive to sustainable development and environmental protection. However, ionic liquids are not suitable for industrial applications since they are not easily separated and recovered in reaction systems.…”