Negishi coupling pyrroles

Dihydropyrrole triflate 55 is smoothly converted to the 2-phenyl derivative 56 under Negishi conditions [53]. This sequence represents a useful alternative to conventional pyrrole Negishi couplings. 

A cross-coupling reaction (Negishi coupling) between A -SEM-pyrrol-2-yl-zinc chloride 618 and the appropriate dibromo derivative catalyzed by a Ni catalyst leads to 2-[4-(l//-pyrrol-2-yl)phenyl]-l//-pyrroles 619 (Scheme 125) <1997CM2876>. The SEM-protecting group can be easily removed by reaction with BU4NF. 

Methoxy-5-(177-pyrrol-2-yl)-2-thienyl]-177-pyrrole 621 was also prepared by a cross-coupling reaction, Stille reaction in this case, between A -SEM-2-(trimethylstannyl)-l/7-pyrrole 620 and 2,5-dibromo-3-methoxythiophene in the presence of a Pd catalyst, followed by nitrogen deprotection (Scheme 126) <1997CM2876>. If Negishi coupling is applied, the main reaction product is, in this case, A -SEM-2,2 -dipyrrole, and the desired compound can be isolated only in trace amount. 

Benzylic-type sulfonium salts derived from thiophene-2- and 3- and furan-2-methanols, where halides are not stable, have been nsed as snbstrates for Suzuki, Stille and Negishi couplings. The 1-Boc-pyrrole-2-methanol analogne was only snccessful in StiUe couplings. An important feature of this method is that triphenyl phosphite was reqnired as the ligand to overcome the problem of reaction of the usual phosphine ligands with the snlfonium salts. ... 

Banwell has developed a new approach to the core associated with several members of the lamellarin class of marine natural products. This approach utilized some interesting pyrrole arylation reactions including a Negishi. cross coupling of the iodopyrrole 46 followed by a double-barrelled Heck cyclization of the resultant arylpyrrole 47 yielding the core structure 48... 

A cross-coupling methodology was also used by Banwell et al. to build the lamellarin framework around the pyrrole core 122 using Negishi and double-barrelled Heck-type reactions to establish key carbon-carbon bonds from 121 <99AJC755>. 

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