Brominated phenolic pyrrole

A brominated diterpene, concinndiol, an isomer of aplysin-20, has been recently described from the alga Laurencia concinna (171). Some simple bromophenols also occur in algae (160, p. 88) and a highly brominated phenolic pyrrole has been found in a marine bacterium (111, 132). 

Another application of CuBrj to bromination of pyrroles was described. 2-(o-Hydroxybenzoyl)pyrrole can be converted to either the 4-bromo or 4,5-dibromo product, depending upon reaction conditions. Use of 3 equiv. of CuBrj gave l27as the major product (72%) whereas 6-6.5 equiv. gave mainly 128(95%). Still higher amounts of CuBrj result in bromination of the phenol ring. <94JHC941>... 

Bromination The five-membered aromatic heterocycles are all more reactive toward electrophiles than benzene is, and the reactivity is similar to that of phenol. These compounds undergo electrophilic bromination. However, reaction rates vary considerably, and for pyrrole, furan and thiophene the rates are 5.6 x 10, 1.2 x 10 and 1.00, respectively. While unsubstituted five-membered aromatic heterocycles produce a mixture of bromo-derivatives, e.g. bromothiphenes, substituted heterocycles produce a single product. 

Bromination of Aromatic Compounds. Phenols, anilines, and other electron-rich aromatic corrqiounds can be monobromi-nated using NBS in DMF with higher yields and higher levels of para selectivity than with Br2 iV-TrimethyIsilylanilines and aromatic ethers are also selectively brominated by NBS in CHCI3 or ecu. A-Substituted pyrroles are brominated with NBS in THF to afford 2-bromopyrroles (1 equiv) or 2,5-dibromopyrroles (2 equiv) with high selectivity, whereas bromination with Br2 affords the thermodynamically more stable 3-bromopyrroles. The use of NBS in DMF also achieves the controlled bromination of imidazole and nitroimidazole. Thiophenes are also selectively brominated in the 2-position using NBS in acetic acid-chloroform. ... 

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