Recent Progress in Amination Enabled by Transition-Metal-Free C(sp2)–O/C(sp2)–S Bond Cleavage Strategy

Abstract

Recently, intense efforts have been dedicated to the development of novel synthetic strategies to access aromatic amines due to their importance in the pharmaceuticals, agrochemicals, materials, and natural product areas. Although numerous transition-metal-catalyzed C–N formation strategies have been described for the preparation of aromatic amines in the past few decades, complementary methods under transition-metal-free conditions are still required. We present the recent advances in the exploration of innovative amination approaches via C(sp2)–O/C(sp2)–S bond cleavage in this review.1 Introduction2 Stoichiometric Base-Promoted Amination3 Base-Catalyzed Amination4 Photoredox-Catalyzed Amination5 Acid-Promoted Amination6 Conclusion and Perspectives

Synthesis of Indoles via Domino Reactions of 2-Methoxytoluene and Nitriles

“…Wang and co-workers presented a KN­(SiMe 3 ) 2 -promoted amination protocol to install various aryl amines onto activated N -heteroaromatic rings . Moreover, there are transition-metal-free mediated amination reactions via C­(sp 2 )–O/C­(sp 2 )–S bond cleavage . Based on these pioneering reports, we envisioned that it might be possible to construct 2-arylindoles from 2-methoxytoluenes and benzonitriles (Scheme c), significantly expanding the synthesis of indoles.…”

“…40 Moreover, there are transition-metalfree mediated amination reactions via C(sp 2 )−O/C(sp 2 )−S bond cleavage. 41 Based on these pioneering reports, we envisioned that it might be possible to construct 2-arylindoles from 2-methoxytoluenes and benzonitriles (Scheme 3c), significantly expanding the synthesis of indoles. Herein, we demonstrate that conditions used for the reversible deprotonation of 2-methoxy toluenes introduced here indeed enable addition to the nitrile and the S N Ar with the methyl ether to expel methoxide.…”