Protic Ionic Liquid as Reagent, Catalyst, and Solvent: 1‐Methylimidazolium Thiocyanate

Abstract

We propose anew concept of the triple role of protic ionic liquids with nucleophilic anions:a)aregenerable solvent, b) aB rønsted acid inducing diverse transformations via general acid catalysis,a nd c) as ource of an ucleophile.T he efficiency of this strategy was demonstrated using thiocyanatebased protic ionic liquids for the ring-opening of donoracceptor cyclopropanes.Awide variety of activated cyclopropanes were found to react with 1-methylimidazolium thiocyanate under mild metal-free conditions via unusual nitrogen attacko ft he ambident thiocyanate ion on the electrophilic center of the three-membered ring affording pyrrolidine-2-thiones bearing donor and acceptor substituents at the C(5) and C(3) atoms,r espectively,i nasingle timeefficient step.T he ability of 1-methylimidazolium thiocyanate to serve as at riplex reagent was exemplarily illustrated by (4+ +2)-annulation with 1-acyl-2-(2-hydroxyphenyl)cyclopropane,epoxidering-opening and other organic transformations.

4‐(Dimethylamino)Pyridinium Azide in Protic Ionic Liquid Media as a Stable Equivalent of Hydrazoic Acid

“…Lastly, we explored the possibility to utilize 4‐(dimethylamino)pyridinium azide within a telescopic synthesis. Thus, alkyl thiocyanates generated by the treatment of benzyl bromide and cyclohexene oxide with an equimolar amount of 1‐methylimidazolium thiocyanate (HMimNCS) [15] were reacted in situ with HDMAPN 3 providing the corresponding (3+2)‐cycloaddition products – 5‐(alkylthio)‐1 H ‐tetrazoles 9 [53] and 10 . Yields of products 6 – 10 were unoptimized, as our goal in this study was only to demonstrate a principal possibility of HDMAPN 3 application in these transformations.…”

“…These considerations along with our endeavors on the use of protic ionic liquids as triple‐role reagents (solvent; source of proton for general acid catalysis; nucleophile) [15] stimulated us to reinvestigate D‐A cyclopropane opening with azide ion as model process aiming to find the reaction conditions suitable for the efficient and eco‐friendly synthesis of polyfunctionalized azides. We explored three different systems containing both azide ion and a proton source: 1) aqueous solution of sodium azide and Brønsted acid (or its salt with an amine); 2) the combination of aqueous NaN 3 and protic ionic liquid (PIL, salt formed by an acid and an organic base with a melting point less than 100 °C); 3) the mixture of PIL and salt of hydrazoic acid with the appropriate Brønsted base (Scheme 1).…”

Synthesis of Heterocycles from Donor-Acceptor Cyclopropanes: A Five-Year Recap

“…Also in 2021, Trushkov, Werz, Andreev, and co-workers demonstrated the use of protic ionic liquid, 1-methylimidazolium thiocyanate, in a reaction with DAC wherein the ionic liquid plays a triple role as a solvent, reagent, and catalyst. 53 The 1-methylimidazolium thiocyanate was prepared by the reaction of N -methylimidazolium chloride with sodium thiocyanate and was isolated as a bench stable compound. Subsequent heating of various DACs in 1-methylimidazolium thiocyanate produced 5-aryl-2-thioxopyrrolidine-3,3-dicarboxylates in good yields.…”