Phenylpyrrole, reduction

Another type of ring contractions occurs when 2-phenylpyrimidines (117) are reduced in an aqueous alcoholic-acetate buffer. Whereas pyrimidines generally are reduced in a one-electron reduction to a dimer,1 2-phenylpyrimidines are reduced to 2-phenylpyrroles (118). The following scheme has been suggested173 [Eq. (86)]. 

In Section III,B it was pointed out that 2-phenylpyrimidines did not follow the general reduction path of pyrimidines but were reduced to 2-phenylpyrroles in a four-electron ring-contraction reaction.174 [Eq. (86)]. 

The reductive ring contraction of 2-phenylpyrimidines to 2-phenylpyrroles involves a cleavage of a carbon-nitrogen bond, followed by attack by a carbanion on an azomethine group [158]. 

Reduction of 4-carbethoxy-2-phenyl-l,3-thiazinone-6 (XLVI) in aqueous alcoholic media yields 2-carbethoxy-4-hydroxy-5-phenylpyrrole (XLVII) in a 4e-process. The first step in the reduction is suggested to be the saturation of the C = N double bond the mechanism of the reductive loss of H2S and C-C bond formation is not yet established [159] ... 

Ruthenium-based catalysts display some utility for electrophilic amination of heteroaromatic substrates. Che and coworkers have found that [Ru(TTP)(CO)J in combination with PhI=NTs will oxidize arenes such as furan, indole, and pyrrole (Fig. 13) [68]. Reactions occur optimally under the action of ultrasound, a rather unusual addendum to the standard protocol for C-H amination. More intriguingly still, iV,A-ditosylated products are isolated in most instances, a finding that is not easily resolved mechanistically. As the substrate profile for this amination process involves only electron-rich heteroaromatics, aziridination of the arene nucleus would seem a likely step along the reaction coordinate. Interestingly, no amination product is observed when stoichiometric [Ru(TMP)(NTs)2] (TMP = tetra(2,4,-6-trimethylphenyl)porphyrin) is mixed with either furan or /V-phenylpyrrole. though a reduction of the starting Ru(VI) complex to a Ru(IV) species is noted... 

Metal NPs combined with conducting polymers were also produced. Johans et al. synthesized polyphenylpyrrole coated silver particles based on the E C mechanism, in which the reversible facilitated IT of Ag+ to the organic phase was followed by its slow irreversible reduction by phenylpyrrole. ° The process was studied by cyclic voltammetry and UV-VIS. 

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