Sulfonic Acid‐Functionalized Ionic Liquids as Metal‐Free, Efficient and Reusable Catalysts for Direct Amination of Alcohols

Abstract

A series of sulfonic acid‐functionalized (SO3H‐functionalized) ionic liquids was synthesized and used as metal‐free, highly selective and efficient catalysts for the direct amination of alcohols. Notably, the activities of the series of SO3H‐functionalized ionic liquids were compared and a 92% isolated yield was obtained using 3‐tetradecyl‐1‐(butyl‐4‐ sulfonyl)imidazolium trifluoromethanesulfonate ([BsTdIM][OTf]) as the catalyst. Importantly, the catalytic system has wide substrate scope including benzylic, allyl, propargylic, aliphatic alcohols with sulfonamide, amide, carbamate, aromatic amine and N‐heterocyclic compounds. Interestingly, the system was also suitable for a multi‐gram scale direct amination of alcohols. Additionally, the reusable nature of [BsTdIM][OTf] makes this protocol more attractive and avoids the disposal and neutralization of acidic catalysts. Moreover, preliminary experiments indicated that this reaction should proceed via an SN1 pathway.

Metal‐Free and Recyclable Route to Synthesize Polysubstituted Olefins via CC Bond Construction from Direct Dehydrative Coupling of Alcohols or Alkenes with Alcohols Catalyzed by Sulfonic Acid‐Functionalized Ionic Liquids

“…Oxybis(methanetriyl)tetrabenzene (5a): White solid; mp 113–114 °C, this compound is known 13 . 1 H NMR (400 MHz, CDCl 3 ): δ =5.39 (s, 2 H), 7.22–7.37 (m, 20 H); 13 C NMR (100 MHz, CDCl 3 ): δ =79.9, 127.3, 127.4, 128.4, 142.2; GC‐MS (EI): [ m/z ] + =350.0.…”

“…Inspired by our previous research on the sulfonic acid‐functionalized ionic liquids‐catalyzed direct amination of alcohols13 and previous reports on carbocation chemistry,4c we envisioned that the formed carbocation intermediate from an alcohol under the action of SO 3 H‐functionalized ionic liquids could participate in a nucleophilic addition of olefins to afford new carbon‐carbon bonds with water as the only by‐product. In addition, the olefin coupling partner can be obtained in situ by the dehydration of the corresponding inexpensive and often easily available alcohols bearing H at the β position.…”

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

“…Thus, direct nucleophilic substitution reactions of alcohols have gained much attention . Previously, we realized direct synthesis of polysubstituted olefins via construction of C‐C bonds from alcohols or alkenes with alcohols and also developed system for direct amination of alcohols , . Generally, carbocations from alcohols were proposed as the active intermediates during the systems.…”

Synthesis of pyranopyrazoles, benzopyrans, amino-2-chromenes and dihydropyrano[c]chromenes using ionic liquid with dual Brønsted acidic and Lewis basic sites

“…In general, a slight decrease in the activity of the catalyst is common and has been reported in several studies (Fang, et al, 2006;Han, et al, 2012;Liu, et al, 2013;Luo, et al, 2014;Wang, et al, 2008). In the current work, although there is no clear explanation for the slight loss of activity, it might be due to the ion exchanges.…”