Transition Metal-Free Heteroarylation of Quinoxaline: Construction of Heteroaryl-Fused Phenazines by Oxidative Coupling

Brønsted acid-mediated mono- and di-substitution of quinoxalines with indoles: a pathway to indolocarbazole-quinoxaline scaffolds

A versatile and efficient protocol for the mono- and di-substitution of quinoxalines with indoles has been developed, offering a direct pathway to indolocarbazole-quinoxaline scaffolds. By optimizing the reaction conditions, selective coupling at the C-2 and C-3 positions of quinoxalines with diverse indole derivatives was achieved under transition metal-free conditions. Substrate scope evaluation revealed broad functional group tolerance and the synthetic utility was demonstrated by gram-scale synthesis and subsequent cyclization into novel indolocarbazole-quinoxalines. Mechanistic studies suggest an ionic pathway, highlighting the potential of this method for constructing biologically relevant heterocyclic architectures.

2-(Thienyl)quinoxaline derivatives and their application in Ir(III) complexes yielding tuneable deep red emitters

The synthesis and characterisation of eleven different 2-(thienyl)quinoxaline species that incorporate different points of functionality, including at the thiophene or quinoxaline rings, are described. These species display variable fluorescence properties in the visible region (λem = 401-491 nm) depending upon the molecular structures and extent of conjugation. The series of 2-(thienyl)quinoxaline species were then investigated as cyclometalating agents for Ir(III) to yield [Ir(C^N)2(bipy)]PF6 (where C^N = the cyclometalated ligand; bipy = 2,2'-bipyridine). Eight complexes were successfully isolated and fully characterised by an array of spectroscopic and analytical techniques. Two Ir(III) examples were structurally characterised in the solid state using single crystal X-ray diffraction; both structures confirmed the proposed formulations and coordination spheres in each case showing that the thiophene coordinates via a Ir-C bond. The photophysical properties of the complexes revealed that each complex is luminescent under ambient conditions with a range of emission wavelengths observed (665-751 nm) indicating that electronic tuning can be achieved via both the thienyl and quinoxaline moieties.

Recent Advances in the Transition-Metal-Free Arylation of Hetero­arenes

Transition-metal-free arylation reactions have attracted considerable attention for economic and environmental reasons over the past 40 years. In recent years, much effort has been made to develop efficient transition-metal-free approaches for the arylation of heteroarenes. Covering the literature from 2015 to early 2021, this review aims to provide a thorough overview of the synthetic and mechanistic aspects of these atom-economical and environmentally benign reactions.

1 Introduction

2 Arylation of Pre-functionalized Heteroarenes

2.1 Arylation of Heteroaryl Halides

2.2 Decarboxylative Arylation of Heteroarenes

3 Direct C–H Arylation of Heteroarenes

3.1 C(sp2)–H Arylation

3.2 C(sp3)–H Arylation

4 N-Arylation of Heteroarenes

5 Summary and Outlook