Copper‐Catalyzed Coupling of Arylethynes and Aryltriazenes to Access Libraries of 1,2‐Diketones and Their Efficacy in Synthesis of Triaryloxazoles, Imidazoles and Diaryl‐Diazepines

Synthesis of 2,4,5-Trisubstituted Oxazoles from Copper-Mediated Benzylic sp3 C-H Aerobic Oxidative Annulation of Ketones and Amines via a Cascade Reaction

The functionalization of sp³ carbons is deemed challenging in synthetic organic chemistry yet has tremendous potential in producing potent organic compounds. A facile synthesis of 2,4,5-trisubstituted oxazoles through an oxidative, copper-catalyzed, and solvent-free annulation is described. Various arylated oxazoles were efficaciously synthesized at a mild temperature from readily available substrates under a molecular oxygen atmosphere. Preliminary mechanistic studies suggested that the reaction proceeds via an anionic-type mechanism and indicated the formation of a keto-imine intermediate. The reaction is notable for the abstraction of six hydrogen atoms, the functionalization of one sp² carbon and two sp³ carbons, and the formation of C-O and C-N bonds.

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

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 Introduction

2 Aryldiazonium Salts and Aryltriazenes as Coupling Partners in Metal-Mediated C–C Cross-Coupling Reactions in ILs

3 Expanding the Scope of Metal-Mediated Cross-Coupling Reactions in ILs

4 Application of ILs in Synthesis and Functionalization of Hetero­cycles

5 Expanding the Scope of Amide Synthesis in ILs

6 Generation and Chemistry of ‘Tamed’ Propargylic Cations in ILs

7 Newer Nitration Methods for Arenes and Heteroarenes in ILs

8 Halofunctionalization in ILs

9 ‘Name Reactions’and Other Widely Practiced Synthetic Transformations in ILs

9.1 The Biginelli Reaction

9.2 Nitrile Synthesis by the Schmidt Reaction

9.3 Rupe Rearrangement

9.4 Synthesis of 1,3-Dioxanes via Prins Reaction in [BMIM(SO3H)][OTf]

9.5 Synthesis of Cyclopropanes and Oxiranes by the Corey–Chaykovsky (CC) Reaction

10 Conclusions and Closing Remarks