2,4- vs 3,4-Disubsituted Pyrrole Synthesis Switched by Copper and Nickel Catalysts

Abstract

A novel and efficient copper or nickel catalyzed highly selective denitrogenative annulation of vinyl azides with aryl acetaldehydes has been developed. 2,4- and 3,4-diaryl substituted pyrroles, which are difficult to synthesize by the reported methods, can be highly regioselectively prepared by this protocol simply switched by the selection of the transition metal catalysts. Compared with the reported acidic or basic conditions for polysubstituted pyrrole synthesis, the present reaction conditions are mild, neutral, and very simple without any additives.

Silver‐Catalyzed Nitrogenation of Alkynes: A Direct Approach to Nitriles through CC Bond Cleavage

“…Furthermore, when 3-(4-methoxyphenyl)-2H-azirine (6), which is potentially generated by the nitrene intermediate, [20] and tetrazole 7 [21,22] were employed as the substrates, the reactions did not proceed (Scheme 4 c and d). These results exclude azirine and tetrazole as intermediates in this transformation.…”

New regioselective synthesis of polyfunctionalized 3-ferrocenyl-1 H -pyrroles under microwave irradiation

“…The ability of ferrocene to undergo reversible one-electron oxidation to the ferrocenium cation, under air or photo-oxidation, is known and has been widely explored. 36 Based on similar reports, 22h, 30,32,36 we presume that, in this catalytic reaction, the ferrocenyl vinyl azide can act as both reactant and catalyst.…”

“…22h, 30,32 Thus, in order to support this initial idea, a control experiment was performed, adding the radical scavenger (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) to the standard synthetic conditions (Scheme 3). From this experiment, only traces of the pyrrole 3a were observed, which suggests that the reaction should follow a radical path in the cyclization process.…”

Cu‐Catalyzed Heterocycle Synthesis

“…Cu(OAc) 2 could catalyze the formation of 2,4-diaryl-substituted pyrroles. This selective polysubstituted pyrrole synthesis could proceed under mild conditions without any acidic or basic conditions [20] CuOTf-catalyzed synthesis of polysubstituted pyrroles from -diazoketones, nitroalkenes, and amines was reported by Lu, Wang, and coworkers. The corresponding polysubstituted pyrroles could be obtained in moderate yields using air as the oxidant.…”