Pyrrolylzinc chloride

The N-pyrrolylzinc chloride 53 undergoes Pd-catalyzed coupling with perfluoroalkyl iodides to afford the 2-substituted pyrroles 54 in good yield [52], Smaller amounts (15-20%) of 2-perfluoroalkanoyl pyrroles, which presumably arise by hydrolysis of the benzylic difluoromethylene group, are also formed. This reaction, which is performed in one pot, also affords 2-phenylpyrrole (75%) and 3-phenylpyrrole (5%) with iodobenzene. Some biphenyl (15%) is also formed. 

Palladium-catalyzed cross-coupling reactions are not restricted to stannane derivatives, however, and other azaheterocyclic carbanion derivatives to have been investigated include l-methyl-2-pyrrolylmagnesium bromide and l-methyl-2-pyrrolylzinc chloride (81TL5319), l-methyl-2-indolymagnesium bromide (81TL5319), l-substituted-2- and 5-imidazolyl-... 

The scope of the Negishi-coupling is not limited to aryl and vinyl halides and sometimes acyl chlorides might also be converted to ketones by this protocol. The 2,3-dihalopyrrole derivative shown in 6.22. was converted into its 2-lithio derivative by selective lithium-halogen exchange at -78 °C. Addition of zinc chloride effected the formation of the appropriate pyrrolylzinc chloride, which was coupled with a functionalised butyroyl chloride in the presence of tetrakis(triphenylphosphino)palladium and furnished the expected 2-acylpyrrole in 61% yield.27... 

The, V-pyrrolylzinc chloride (75) can be generated and coupled in situ with aryl bromides to give the expected 2-arylated pyrroles 77 in good to excellent yields [62]. Some aryl chlorides and iodides also couple with 75. 

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