2- Bromopyrrole

Treatment of pyrrole, 1-methyl-, 1-benzyl- and 1-phenyl-pyrrole with one mole of A -bromosuccinimide in THF results in the regiospecific formation of 2-bromopyrroles. Chlorination with IV-chlorosuccinimide is less selective (8UOC2221). Bromination of pyrrole with bromine in acetic acid gives 2,3,4,5-tetrabromopyrrole and iodination with iodine in aqueous potassium iodide yields the corresponding tetraiodo compound. 

Although pyrrolyl halides are well-known compounds, their instability to acid, alkali, and heat precludes their commercial availability. Since pyrrole is a very reactive, Jt-excessive heterocycle, it undergoes halogenation extremely readily [6, 7], For example, the labile 2-bromopyrrole, which decomposes above room temperature, is a well-known compound, as are A-aIkyl-2-halopyrroles, readily prepared by direct halogenation, usually with NBS for the synthesis of bromopyrroles [8, 9], The 2-halopyrrole is usually the kinetic product but the 3-halopyrrole is often the thermodynamic product, and this property of halopyrroles can be exploited in synthesis. For example, A-benzylpyrrole (1) can be dibrominated to give 2 as the kinetic product, which rearranges to 3 upon treatment with acid [10, 11]. Other A-alkyl-2,5-dibromopyrroles are available in this fashion. 

Using 2-bromopyrrole 72, Burgess has synthesized 2-arylpyrroles 73 in excellent yield [61], The resulting hydrolyzed pyrroles 74 were used to prepare 3,5-diaryl BODIPY dyes. 

Substituted Pyrroles from N-tert-Butoxycarbonyl-2-bromopyrrole ... 

CAi90) 123047). The isolation of 2-chloro-5-formylpyrrole from the Vilsmeier-Haack formylation of 2-bromopyrrole (75JOC3161) can be rationalized in terms of an addition-elimination reaction of the intermediate azafulvenium cation (Scheme 82). Displacement... 

Regioselective bromination. This reagent is superior to NBS for bromination of pyrrole to provide 2-bromopyrrole. After conversion to the N-boc derivative,... 

The first intermolecular C-N bond-forming reactions between substituted 2-bromopyrroles 1450 and 1453 with primary (Tpropanamine, 2-methoxy-l-ethanamine, (4-methoxyphenyl)methanamine, cyclopropanamine, cyclobuta-namine), and cyclic secondary amines (pyrrolidine, morpholine, 1-methylpiperazine, ethyl tetrahydro-l(27/)-pyrazi-necarboxylate, 1-phenylpiperazine, l-(3-phenyl-2-propenyl)piperazine) 1451 were performed using Pd2(dba)3 as catalyst with BINAP as the ligand. The aminations proceeded in the presence of Bu ONa at 80-100 °C in 31-93% yields (Equations 301 and 302) <2004TL769>. However, when the above optimized conditions were applied to the coupling reaction of pyrrole 1450 and acyclic secondary amines such as di- -butylamine, diphenylamine and dipropenylamine, no reaction was observed. 

Dipyrromethenes (e.g., (42)) with a symmetrical arrangement of substituents can be prepared by self-condensation of 2-unsubstituted pyrroles (43a) or the corresponding pyrrole-2-carboxylic acids (43b) in boiling formic acid containing hydrobromic acid (Scheme ll).27 The synthetically more useful unsymmetrically substituted dipyrromethene salts (e.g., (44)) are best obtained by the condensation of a 2-formylpyrrole (45) with a 2-unsubstituted pyrrole (46) in the presence of acid (usually HBr) (Scheme 12). Heating of 2-bromomethylpyrroles (47) with 2-bromopyrroles (48) (synthesized by bromination of 2-unsubstituted pyrroles, (49)) in presence of bromine also gives good yields of unsymmetrical dipyrromethene hydrobromides (50) (Scheme 13). 

Although labile, 2-bromopyrrole (15) can be prepared from pyrrole and protected in situ to give 2-bromo-l-tosylpyrrole (16) in 80% yield [25],... 

N-tert Butoxycarbonyl-2-bromopyrrole 1H-Pyrrole-1-carboxylic add, 2-bromo-, 1,1-dimethylethyl ester (12) (117657-37-1)... 

SUBSTITUTtD PYRROLES FROM N-tert-BUTOXYCARBONYL-2-BROMOPYRROLE N-tert-BUTOXY-2-TRIMETHYLSILYLPYRROLE... 

In the present procedure, pyrrole is brominated under mild conditions to the very labile 2-bromopyrrole using 1,3-dibromo-S.5-dimethylhydantoin the latter reagent gives better results than the previously employed N-bromosuccinimide. Direct conversion of 2-bromopyrrole to Its more stable N-tert-butoxycarbonyl derivative... 

Although unstable compounds, 2-bromo- and 2-chloropyrrole (also using SO2CI2) can be prepared by direct halogenation of pyrrole with the A-halo-succinimides 2-bromopyrrole can be conveniently prepared using l,3-dibromo-4,4-dimethylhydantoin and can be stabilised by conversion into its N-t-butoxycarbonyl derivative. Formation of A-tosyl derivatives is also recommended for stabilising 2-bromopyrrole. 

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