Enhancement of S_NAr reactions by CH₃SO₃⁻ ionic liquid and organic solvent dimethylformamide as bifunctional organocatalysts: A mechanistic study

Abstract

Quantum chemical analysis is presented for the mechanism of S N Ar reaction of p-fluoronitrobenzene and p-anisidine promoted by [C 4 C 1 im][CH 3 SO 3 ] and by dimethylformamide (DMF), experimentally observed by Welton and co-workers (Org. Lett. 2007, 9, 5247-5250). We find that [C 4 C 1 im] + assists the detachment of the fluoride leaving group, while [CH 3 SO 3 ] À supplies partial negative charge to the nucleophile NH 2 to enhance the reactivity. We also show the moderate yield (22.1%) in DMF can also be understood by considering the solvent molecule as a bifunctional organocatalyst. The calculated Gibbs free energies of activation are in excellent agreement with the experimental observations.

Ionic Liquids as Organocatalysts for Nucleophilic Fluorination: Concepts and Perspectives

“…Since the aliphatic fluorination is just a small part of S N 2 reactions, many advantageous properties of ILs will surely stimulate further developments in other nucleophilic reactions with a variety of substrates and organocatalysts. S N Ar reactions seems to remain a largely unexplored field in this respect [ 79 , 80 , 81 , 82 ]. Experimental and theoretical examination of using ILs as solvents/promoters for efficient and selective S N Ar fluorination in metal-free conditions would be highly desirable.…”