Copper-mediated C-N bond formation

An impressive range of nucleophiles was successful for arylboronic acids in the presence of Cu(OAc)2 and base, which included amine, anilines, amides, imines, ureas, carbamates, sulfonamides, and aromatic heterocycles (e.g., imidazoles, pyrazoles, triazoles, tetrazoles, benzimidazoles, and indazoles) (Equation (226)) 996 997 1000-1011 For all the reactions investigated with A-nucleophiles, the use of Et3N resulted in yields superior to those obtained with pyridine, but pyridine was the base of choice for the preparation of imidazole derivatives from heteroarenes. For the tetrazole, NMO and DBU were studied as alternative bases. There are mechanistic studies.999,1002-1013 

A one-pot two-step process using two different arylboronic acids for 3-iodoindazole furnished 1,3-diaryl indazoles (Equation (227)).1014 

It was shown that the partner could be extended with a vinyl group (Equations (228) and (229)).1015 1016 The best yields of the desired coupling products were obtained in the presence of stoichiometric amounts of Cu(OAc)2 exposed to air. 

The reaction was made catalytic when a suitable oxidant of Cu(i) species was used. In the presence of catalytic amount of copper salt, aryl- (Equation (230)) and alkenylboronic acids (Equation (231)) smoothly reacted with A-nucleophiles, such as imidazoles, at room temperature.1012,1013,1015,1017,1018 TEMPO, pyridine A-oxide, oxygen were effective reoxidants to recycle the copper catalyst. 

Oxidant 02, air, TEMPO in air, pyridine A/-oxide Base Et3N, pyridine 

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