Synthesis of 1,2′- and 1,3′-bipyrroles from 2- and 3-nitropyrroles

Five‐Membered Heterocycles: Pyrrole and Related Systems

“…Alternatively, similar chemistry may also be accomplished using tin or indium as the reducing agents [742], while application of 1,4-diketones instead of anhydrides has provided efficient access to 1,2 0 -and 1,3 0 -bipyrroles [743]. Finally, it should also be mentioned that determination of the second-order rate constants of the reactions of a series of pyrroles with benzhydrylium ions in acetonitrile provided the basis for a nucleophilicity scale, where 1-triisopropylsilylpyrrole was the least nucleophilic member and 3-ethyl-2,4-dimethylpyrrole was the strongest nucleophile, comparable to enamines in its reactivity [744].…”

A General Route to 1,3′-Bipyrroles

“…A variant of the Paal–Knorr reaction that uses a keto-ketal instead of a diketone has likewise been applied to 3-aminopyrroles. , Again, the pyrrole unit that is formed has been unsubstituted. The classical Paal–Knorr reaction itself has been used with 3-aminopyrroles ,, and a number of 1,4-diketones.…”

N‐Substituted pyrrole synthesis by Paal–Knorr condensation using recyclable cationic exchange resin in water

“…One of the most important approaches to pyrrole synthesis is the Paal–Knorr reaction, which involves the reaction of 1,4‐dicarbonyl compounds and their masked equivalents with primary amines. Generally, the most used conditions include p ‐TsOH in toluene or benzene [7], AcOH/methanol [8], TiCl 4 in toluene [5a], Ti(OPr) 4 in benzene [9], Bi(OTf) 3 /[bmim]BF 4 [10], Bi(NO 3 ) 3 in CH 2 Cl 2 [11]. However, some of these methods often suffer from certain drawbacks, such as hazardous organic solvents, metals, and high costs.…”