In recent years, environmental and economic reasons have motivated the development of transition metalfree carbon-carbon bond forming reactions and some excellent reviews have covered this research area of particular interest for pharmaceutical industry. However, none of these reviews has been specifically dedicated to summarize and discuss the results achieved in the rapidly growing field of the transition metal-free direct (hetero)arylation reactions of heteroarenes. This review, which covers the literature from 2008 to 2014, aims to provide a thorough insight of the synthetic and mechanistic aspects of these atom economical and environmental benign reactions also highlighting their advantages and possible disadvantages compared to conventional methods for the synthesis of arylheteroarenes and biheteroaryls via transition metal-catalyzed reactions. 1. Introduction 2. Direct (Hetero)arylation of Heteroarenes with (Hetero)aryl Halides or Pseudohalides 3. Direct (Hetero)arylation of Heteroarenes with (Hetero)aryl Iodonium Salts 4. Direct Arylation of Heteroarenes with Anilines Nitrosated in situ or Arylhydrazines 5. Direct Arylation of Benzothiazoles with Aryl Aldehydes 6. Direct (Hetero)arylation of Heteroarenes with (Hetero)arylmetals 7. Conclusions
A new hole-transport material (HTM) based on the 1,3,4-oxadiazole moiety (H1) was prepared through a single-step synthetic pathway starting from commercially available products. Thanks to a deep HOMO level, H1 was used as HTM in CH3 NH3 PbBr3 perovskite solar cells yielding an efficiency of 5.8%. The reference HTM (Spiro-OMeTAD), under the same testing conditions, furnished a lower efficiency of 5.1%. Steady-state and time-resolved photoluminescence of the thin films showed good charge-extraction dynamics for H1 devices. In addition, H1 shows a large thermal stability and completely amorphous behavior (as evaluated by thermal gravimetric analysis and differential scanning calorimetry).
This review with 453 references covers the literature up to the end of April 2015 on the transition metal-catalyzed direct C-H (hetero)arylation reactions of heteroarenes with one heteroatom in which high regioselectivity has been gained by the use of removable protecting/blocking substituents or traceless directing groups. Particular attention has been devoted to illustrate the typical features of these methods, and to summarize the synthetic procedures used for the introduction of removable protecting/blocking groups in the heteroarene substrates and their subsequent removal from the reaction products. The limitations related to the use of protecting/blocking substituents and directing groups, such as an increase in synthetic steps or the fact that, in many cases, the (hetero)arylation reactions assisted by directing groups involve only C-H bonds ortho to the directing group, will also be highlighted
The significant number of papers and reviews published in this last decade testifies to the utility of the transition-metal-catalyzed direct C–H (hetero)arylation reactions of (hetero)arenes as efficient and powerful tools for the step- and atom-economical, regio- and chemoselective synthesis of natural and unnatural compounds. However, no review has so far been devoted to summarizing the application of these reactions in the synthesis of biologically active compounds. This review with 341 references aims to fill this gap, providing a comprehensive picture of the transition-metal-catalyzed intra- and intermolecular direct C–H (hetero)arylation reactions of (hetero)arenes with (hetero)aryl halides or pseudohalides that have been used as key steps of syntheses of unnatural biologically relevant compounds including pharmaceutical targets, up to the end of September 2015. Attention has also been directed to provide a brief description of the biological properties of the synthesized compounds. 1 Introduction 2 Syntheses via Intramolecular Direct (Hetero)arylation of (Hetero)arene Derivatives 3 Syntheses via Intermolecular Direct (Hetero)arylation Reactions 3.1 Of Arenes 3.2 Of Five-Membered Heteroarenes with One Heteroatom 3.3 Of Five-Membered Heteroarenes with Two Heteroatoms 3.4 Of Five-Membered Heteroarenes with Three and Four Heteroatoms 3.5 Of Five-Membered Heteroarenes Fused to a Six-Membered Heteroarene 3.6 Of Five-Membered Heteroarene Moieties of Tricyclic Heteroarenes 3.7 Of Six-Membered Heteroarenes 4 Syntheses of Nitrogen-Containing Polycyclic Heteroarene via One-Pot Palladium-Catalyzed Domino Direct Arylation/N-Arylation Reactions 5 Conclusion
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