2,5-Dimethylpyrrole, protecting

The large scale preparation of orthogonally protected pyrrole tricarboxylic acid derivatives (i.e., 92) was reported. A key step was the selective a-chlorination of a 2,4-dimethylpyrrole intermediate that was derived from the Knorr pyrrole synthesis. 

A simple, rapid, and reliable viscometric technique for evaluating the protective capacity of commercially available materials as inhibitors of ozone-induced polymer chain scission has been described (1). This work included the results of an evaluation of several chemicals such as A,A -di-sec-butyl-p-phenylenediamine, nickel dibutyl di-thiocarbamate, l-(m-aminophenyl)-2,5-dimethylpyrrole, and 2,6-di-tert-butyl-4-methyl-phenol as antiozonants A,A -di-sec-butyl-p-phenylenediamine exhibited superior inhibiting characteristics. However, because of the potential toxic effects and relatively high vapor pressure of this chemical, its use is considered impractical. 

The 2H- and 3Af-pyrrolium cations are essentially iminium ions and as such are electrophilic they play the key role in polymerisation (see 16.1.8) and reduction (16.7) of pyrroles in acid. In the reaction of pyrroles with hydroxylamine hydrochloride, which produces ring-opened 1,4-dioximes, it is probably the more reactive 37f-pyrrolium cation that is the starter. Primary amines, RNH2, can be protected, by conversion into l-R-2,5-dimethylpyrroles (16.16.1.1), recovery of the amine being by way of this reaction with hydroxylamine." ... 

Scheme 12, 2,5-Dimethylpyrrole and 2,2 2 trichloroethoxycarbonyl(Troc) protecting groups for enzymatic synthesis of lactosamine.

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