Cu-Catalyzed Aerobic Oxidative N–N Coupling of Carbazoles and Diarylamines Including Selective Cross-Coupling

Abstract

A Cu-catalyzed method has been identified for aerobic oxidative dimerization of carbazoles and diarylamines to the corresponding N-N coupled bicarbazoles and tetraarylhydrazines. The reactions proceed under mild conditions (1 atm O, 60-80 °C) with a catalyst composed of CuBr·dimethylsulfide and N, N-dimethylaminopyridine. Reactions between carbazole and diarylamines show unusually selective cross-coupling, even with a 1:1 ratio of the two substrates. This behavior was found to arise from reversible formation of the tetraarylhydrazine. Formation of this species is kinetically favored, but cleavage of the N-N bond under the reaction conditions leads to selective formation of the thermodynamically favored cross-coupling product.

Cu(OTf)2‐Mediated Cross‐Coupling of Nitriles and N‐Heterocycles with Arylboronic Acids to Generate Nitrilium and Pyridinium Products**

“…This is clearly mechanistically related to previously reported Cu-mediated N-N coupling reactions. [44,45] Consistent with these previous reports,our EPR data suggests that these processes proceed via single electron oxidation of the aniline by Cu II ;h owever,i mportantly,t he resulting aminium radical does not appear to be free in solution and attempts to intercept these species were universally unsuccessful (Table S6). In contrast to ap reviously proposed mechanism, [44] our data suggests formation of the NÀNb ond at the metal or within the solvent cage.This would deliver the symmetrical hydrazine product, consistent with previous observations.…”

Tunable Electrochemical C−N versus N−N Bond Formation of Nitrogen‐Centered Radicals Enabled by Dehydrogenative Dearomatization: Biological Applications

“…First, the generality of the cyclization product was tested (Table 1, standard condition A). As shown, ab road spectrum of functional groups was tolerated with good to quantitative efficiency.Specifically,electron-donating groups, such as alkyl (4,5,15,16), ether (6,7,17,18), and thioether groups (9), and electron-withdrawing groups including fluoro (8, 22, 23, 25, 28, 29), chloro (2, 22, 26, 28), bromo (27), and trifluoromethoxy (10,19)m oieties reacted smoothly in the aqueous system. Interestingly,t he groups that were electrochemicaly oxidative and reductive labile were intact in moderate yields.T his observation was exemplified by the amino (20,21), and thioether groups for the electrochemical oxidative moieties and by the aldehyde (32), ketone (31), and ester (11,33)g roups for the reductive labile moieties.…”

“…Conventional transition-metal-catalyzed oxidative coupling of secondary amines with oxidants is the primary procedure for their preparation. [15] In view of these privileged structures and our interests [16] in organic electrochemistry, [17] we envision that by controlling one of the key factors in electrochemistry,namely,the current density,the distinctive target compound might be furnished in at unable manner through transition-metal-and exogenous oxidant-free electrochemical dehydrogenative NCR strategies.T he hypothesis was based on the principle that the current density is proportional to the reaction rate at the electrode surface,a nd hence correlates to the concentration of the reactive intermediate species.…”

Mechanistic insights into copper-catalyzed aerobic oxidative coupling of N–N bonds

“…These strategies include electrochemical [7][8][9][10] and aerobic oxidative coupling methods. [11][12][13][14][15][16][17][18] Homogeneous Cu catalysts are featured prominently in the latter methods (Scheme 1A), but the mechanism of these reactions has received little attention.…”