Recent advances in synthetic methodologies for transition metal-free Ullmann condensation reactions

Abstract

Different methodologies for transition metal-free Ullmann condensation reactions.

Diaryl Ether: A Privileged Scaffold for Drug and Agrochemical Discovery

“…Besides, the metal-catalyzed cross-coupling reactions, such as the Ullmann-type coupling reaction, the Buchwald-Hartwig coupling reaction, and the Chan-Lam reaction, have been widely studied to synthesize the DE scaffold, of which the type and dosage of catalysts, reaction conditions, substrate scopes, and chemoselectivity have undergone continuous improvements and innovations . Furthermore, the lately developed superbase system (such as KOH/DMSO) and diaryliodonium salts-mediated metal-free methods for the construction of the C–O bond also provided alternative pathways for the synthesis of the DE framework, which greatly expanded the substrate scope and avoided the drawbacks of organometallic chemistry . The above-introduced synthesis methods lay a solid foundation for the discovery and exploration of medicines and agrochemicals featuring a DE scaffold.…”

“…240 Furthermore, the lately developed superbase system (such as KOH/DMSO) 241 and diaryliodonium salts 242 -mediated metal-free methods for the construction of the C−O also provided alternative pathways for the synthesis of the DE framework, which greatly expanded the substrate scope and avoided the drawbacks of organometallic chemistry. 243 The above-introduced synthesis methods lay a solid foundation for the discovery and exploration of medicines and agrochemicals featuring a DE scaffold.…”

Deep eutectic solvents: cutting-edge applications in cross-coupling reactions

“…Recently, most of these hurdles have been circumvented via the development of greener synthetic methodologies, such as the utilization of recyclable heterogeneous catalysts, metal-and ligandfree conditions, microwave-and ultrasound-assisted synthesis, and the deployment of greener solvents, importantly DESs. 164 It is needless to state that the choice of an appropriate reaction solvent is of crucial importance for successful synthesis and implementation of DESs, as non-toxic, recyclable and insensitive solvents towards moisture, thus making the century-old Ullmann reaction appropriate test case in the domain of synthetic organic chemistry.…”

Transition Metal‐Free, Base‐Induced Arylation of Amino Acids: Synthesis of N‐(para‐Substituted phenyl)amino‐2‐carboxylic acids

“…It is notable that despite enormous improvements in C–C homologation, the scope of cross‐coupling techniques to form (hetero)aryl C–N bonds still lags, comparatively . This may be attributed to the sensitivity of functional groups, with respect to requisite bases and aminating agents, and to the prevalence of substituent (e. g., –OH & –NH) effects on the (hetero)aryl halide ring .…”