2- Pyrrole-phenyl iodide

In the 2-position, the Suzuki coupling of WBoc-pyrrole-2-boronic acid with phenyl iodide gave a moderate yield of the 2-phenyl product 20 (Scheme 11). With bromobenzene the yield was low. The best results were obtained with rr-deflcient arenes. The same coupling with indole derivatives gave even lower yields of arylated products. Homocoupling of the heterocycle is responsible for the major by-product. The boronic acid group... 

Moreover, 2,4-disubstituted pyrroles can be synthesized from N,0-acetal 23b, which in turn can be obtained by three-component couphng of sulfonamide 21a, methoxyallene and phenyl iodide (08T809). The aryl group thus inserted into the aUene is part of the coupling process and does not add any extra steps to the sequence. Subsequent RCM and aroma-tization furnished pyrrole 13c in 54% isolated yield the reduced yield is probably due to the steric hindrance of N,0-acetal 23b resulting in less efficient ring closure (Scheme 7). 

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. 

Phase-transfer catalysis was found <1996CHEC-II(7)1> to be successful for N-substitution of the furo[3,2-/ ]pyrrole system. The reaction of 81a with methyl iodide or benzyl chloride gave 81b and 81c derivatives. Methyl 4-acetyl-2-[3-(trifluoromethyl)phenyl]furo[3,2-3]pyrrole-5-carboxylate 82 was obtained by reacting 81a in boiling acetic anhydride (Scheme 6) <2005CEC311>. 

BusSnH-mediated intramolecular arylations of various heteroarenes such as substituted pyrroles, indoles, pyridones and imidazoles have also been reported [51]. In addition, aryl bromides, chlorides and iodides have been used as substrates in electrochemically induced radical biaryl synthesis [52]. Curran introduced [4-1-1] annulations incorporating aromatic substitution reactions with vinyl radicals for the synthesis of the core structure of various camptothecin derivatives [53]. The vinyl radicals have been generated from alkynes by radical addition reactions [53, 54]. For example, aryl radical 27, generated from the corresponding iodide or bromide, was allowed to react with phenyl isonitrile to afford imidoyl radical 28, which further reacts in a 5-exo-dig process to vinyl radical 29 (Scheme 8) [53a,b]. The vinyl radical 29 then reacts in a 1,6-cyclization followed by oxidation to the tetracycle 30. There is some evidence [55] that the homolytic aromatic substitution can also occur via initial ipso attack to afford spiro radical 31, followed by opening of this cyclo-... 

In connection with the elucidation of the structures of the products obtained upon reaction of the tropone (496) with perchloric acid, the 6-methoxy-substituted derivatives have been prepared by reaction of (496) with methyl iodide and silver fluoroborate. -Comparison of u.v. spectra indicated that the salts between the tropones (496) and perchloric acid were 6-hydroxy-derivatives of the perchlorate of (497). U.v. and n.m.r. spectra of the systems (496)—(499) are discussed and their properties and reactivities compared with the corresponding JV-phenyl-pyrrole analogue. A preliminary report of the polarographic, i.r., and u.v. spectroscopic properties, as well as the dipole moments, of both the C-annelated systems (496) and (497) without methyl groups in the thiophen ring and also the ion (500) with alkyl, hydroxy, and methoxy-groups in the seven-membered ring has been published. Values of piirR+ between 6 and 7 have been obtained for this system. The spectroscopic properties of metallocene derivatives such as (501)—(503) have also... 

---