5- Bromopyrrole-2-carboxylate

A novel Pd-catalyzed asymmetric annulation was reported between 5-bromopyrrole-2-carboxylate esters and vinyl aziridines <07OL2357>. The resulting pyrrolopiperazinones such as 58 served as key intermediates in the enantioselective synthesis of longamide B and a number of other pyrrole alkaloids. 

Acid-mediated hydrolysis of 5-halopyrrole-2-carboxylates provides access to 5-carboxy-3-pyrrolin-2-ones, but this transformation often lacks the regioselectivity of other methods. This reaction was first reported by Siedel (1943LAC144). In a more recent example, Battersby and coworkers have treated 5-bromopyrrole-2-carboxylate 548 with sulfuric add in methanol, and a mixture of 3-pyrrolin-2-ones 549 and 550 was obtained in low yield (Scheme 156 1988PT(1)1557). These reaction conditions led to both hydrolysis of the bromine and deprotection of the <-butyl ester followed by decarboxylation. In a related reaction involving a symmetrical substrate, Lugtenberg and de Groot converted 5-bromo-2-trichloroacetyl-3,4-dime-thylpyrrole into 3,4-dimethyl-3-pyrrolin-2-one via treatment with NaOH (1982MI2). 

Li C-J, Schmitz FJ, Kelly-Borges M (1998) A New Lysine Derivative and New 3-Bromopyrrole Carboxylic Acid Derivatives from Two Marine Sponges. J Nat Prod 61 ... 

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). 

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

A marginal, although interesting chemical route to PPy is the decomposition of 3-bromopyrrole and 3,4-dibromopyrrole. " These chemicals can be easily obtained, either from the decarboxylation of the corresponding 2-pyrrole carboxylic acids, or by deprotection of the N-silylated precursors. They are quite stable in solutions, but do polymerize very quickly in the pure state, with evolvement of gaseous hydrobromic acid. The resulting polymers have been produced and characterized. They were found to correspond to doped PPy, very likely by bromide ions. 

---