Substrate Controlled Regioselective Bromination of Acylated Pyrroles Using Tetrabutylammonium Tribromide (TBABr₃)

Abstract

Electrophilic bromination of pyrroles bearing carbonyl substituents at C-2 typically results in a mixture of the 4- and 5-brominated species, generally favoring the 4-position. Herein, we describe a substrate-controlled regioselective bromination in which tetra-butyl ammonium tribromide (TBABr) reacts with pyrrole-2-carboxamide substrates to yield the 5-brominated species as the predominant (up to >10:1) product.

Regioselectively Halogenated Expanded Porphyrinoids as Building Blocks for Constructing Porphyrin–Porphyrinoid Heterodyads with Tunable Energy Transfer

“…17b After our repeated trials, we figured out that L2-Br-C was converted into L1-Br-C in a high yield of 83% by treatment with NaBH 4 in a mixture of tetrahydrofuran (THF) and MeOH. 21 In turn, a further reflux of the toluene solution of L1-Br-C with a base in a way similar to that for L5-Br-B afforded the desired L5-Br-C in 85% yield (Scheme 1c). The 1 H NMR spectrum of L5-Br-C in CDCl 3 is apparently different from those of L5 and L5-Br-A/B; the corresponding α-H signal of the confused pyrrole ring C was diminished (i.e., no signal around 6.9 ppm) (Figure 1d).…”

Synthetic utility of biomimicking vanadium bromoperoxidase and n-tetrabutylammonium tribromide (TBATB) in organic synthesis

“…Pyrroles containing various amides group at C-2 position worked well, and 5-brominated products were achieved in good to excellent yields. 62…”

“…Pyrroles containing various amides group at C-2 position worked well, and 5-brominated products were achieved in good to excellent yields. 62 3.1.2 Bromination of aryl methyl ketones. Aryl methyl ketones are easily brominated at αto the carbonyl group employing TBATB as an efficient brominating agent in such kind of transformation.…”

Electrochemical Umpolung of Bromide: Transition-Metal-Free Bromination of Indole C–H Bond

“…Aromatic bromides are an important class of compounds, which are commonly utilized as the coupling partner in transition-metal-catalyzed cross-coupling reactions [55,56,57,58,59,60,61,62,63,64,65,66,67]. Thus, the development of a synthetic method of arylbromides has attracted tremendous efforts [68,69,70,71,72,73,74,75,76,77,78,79,80,81,82]. Among them, much progress has been made on palladium-catalyzed regioselective bromination of C–H bonds using different agents.…”