Recent Advances in the Synthesis of Diverse Libraries of Small-Molecule Building Blocks in Ionic Liquids (ILs)

Abstract

The Account describes recent advances, from the authors’ laboratories, in the synthesis of diverse libraries of small-molecule building blocks employing ionic liquids (ILs). The ability of ILs to act as catalysts/promoters/solvents for electrophilic and onium ion chemistry, as well as in metal-mediated cross-coupling reactions, and the potential to sequence/hyphenate these methods, have opened up new opportunities for facile assembly of functional small molecules with increased complexity from readily available precursors. While Brønsted acidic IL/IL solvent mixtures are suitable media for carbocation and onium ion chemistry, piperidine-appended IL/IL solvent mixtures can successfully catalyze a variety of base-catalyzed reactions. Several widely practiced transformations including ‘name reactions’ were adapted and performed efficiently in ILs.1 Introduction2 Aryldiazonium Salts and Aryltriazenes as Coupling Partners in Metal-Mediated C–C Cross-Coupling Reactions in ILs3 Expanding the Scope of Metal-Mediated Cross-Coupling Reactions in ILs4 Application of ILs in Synthesis and Functionalization of Hetero­cycles5 Expanding the Scope of Amide Synthesis in ILs6 Generation and Chemistry of ‘Tamed’ Propargylic Cations in ILs7 Newer Nitration Methods for Arenes and Heteroarenes in ILs8 Halofunctionalization in ILs9 ‘Name Reactions’and Other Widely Practiced Synthetic Transformations in ILs9.1 The Biginelli Reaction9.2 Nitrile Synthesis by the Schmidt Reaction9.3 Rupe Rearrangement9.4 Synthesis of 1,3-Dioxanes via Prins Reaction in [BMIM(SO3H)][OTf]9.5 Synthesis of Cyclopropanes and Oxiranes by the Corey–Chaykovsky (CC) Reaction10 Conclusions and Closing Remarks

Aryltriazenes as Coupling Partners in the Hiyama, Hiyama‐Suzuki and Hiyama‐Heck Cross‐Coupling Reactions Using Conventional and Ionic Liquid Reagents and Solvents

“…The next phase of the study focused on the development of “hyphenated” Hiyama‐Suzuki (H−S) and Hiyama‐Heck (H−H) reactions. Table 5 summarizes the results for a stepwise process (Figure 5) in which the p‐bromobiphenyl, the product of the Hiyama coupling (via entry 3, Table 4), reacts by Suzuki and Heck coupling in [BMIM][X] as solvent, with [PAIM][NTf 2 ] as basic‐IL [9] and with [Pd] catalyst under MW, without any additive or ligand.…”

“…[8] In previous studies, we demonstrated the potential of aryldiazonium salts and aryltriazenes as coupling partners in the Suzuki, Heck, and Sonogashira reactions, employing ionic liquids (ILs) as solvents, in combination with acidic or basic ILs as promoters and catalysts, generating diverse libraries of small molecule building blocks. [9,10] In continuation, we report here on the utility of aryltriazenes as coupling partners for the Hiyama coupling, and examine the influence of conventional and ionic liquid (IL) reagents and solvents. We also report on the stepwise and sequential/tandem Hiyama-Suzuki (HÀ S) and Hiyama-Heck (HÀ H) reactions in IL solvents, employing basic and Brønstedacidic ILs.…”