Light-Promoted Low-Valent-Tungsten-Catalyzed Ambient Temperature Amination of Boronic Acids with Nitroaromatics

Abstract

Triggering C−N bond formation with nitroaromatics and boronic acids at mild conditions is highly desirable, since most prior works were carried out under harsh conditions and sometimes suffered from poor chemo-or regioselectivity. Herein, a low-valent-tungsten-catalyzed reaction that enables the ambient temperature amination of boronic acids with nitroaromatics is disclosed. With readily available W(CO) 6 as a precatalyst under external-photosensitizer-free conditions, nitroaromatics smoothly undergo C−N coupling reactions with their boronic acid partners, delivering structurally diverse secondary amines in good yields (>50 examples, yields up to 96%). This methodology is both scalable and highly chemoselective and engages both aliphatic and aromatic boronic acid partners. The catalysis is initiated by the deoxygenation of nitroaromatics by a trans-[W(CO) 4 (PPh 3 ) 2 ] (trans-W, PPh 3 = triphenylphosphine) complex, which forms in situ via ligand replacement.

Direct Reductive Coupling of Nitro Compounds for the Synthesis of Advanced Amines

“…Oxygen-atom transfer then occurred in the presence of PPh Song, Xu, Cai et al also developed a UV-light-promoted C-N coupling under the catalysis of low-valent tungsten (Scheme 15). 27 The absence of the tungsten catalyst and light restrained the reaction. An obvious erosion of the re-…”

Reductive Arylation of Nitroarenes with Chloroarenes: Reducing Conditions Enable New Reactivity from Palladium Catalysts

“…Strategies for the reductive arylation of nitroarenes have thus far relied on the in situ conversion of the nitroarene to a transient, electrophilic nitrosoarene, which is trapped with a nucleophilic carbon source (Ar-[M]) or aryl radical . In general, the propensity of nitrosoarenes to undergo deleterious over-reduction and dimerization necessitates the use of more reactive nucleophilic carbon sources, such as aryl Grignard reagents. − Despite recent advances enabling the use of less reactive arylboronic acids, − arylboronic acids are less available than chloroarenes (∼180× fewer commercially available, Scheme B), adding synthetic complexity. Engagement of aryl chlorides would be simplest via oxidative addition to low-valent palladium or nickel catalysts, but the resulting arylpalladium and arylnickel intermediates are not known to form new C–N bonds with nitroarenes.…”

Low-valent-tungsten catalysis enables hydroboration of esters and nitriles

“…10 Inspired by these works, our group has recently described an efficient tungsten-catalyzed [W(CO) 4 -bpy-Me] homogeneous system for controllable oxidative dehydrogenative coupling of anilines to selectively produce azoaromatics and azoxyaromatics as well as 2-substituted indolone N -oxides by simply appropriately choosing the reaction solvent. 11…”

“…Specifically, we envisaged that the characteristics of low-valent tungsten catalysts to provide multiple coordination geometries together with their high Lewis acidity when compared with late-transition metals would be particularly beneficial in the activation of challenging compounds such as esters and nitriles. 8–11 As part of our research interest in tungsten catalysis and olefin functionalization, 11,17 we describe here the successful implementation of this goal, culminating in the establishment of the first low-valent-W-catalyzed hydroboration of esters and nitriles.…”