The methyl groups of the pyrroles Ia and IIa react with sulphuryl chloride to give dichloromethyl derivatives which hydrolyze to aldehydes. The pyrrole Ia also forms a trichloromethyl derivative which hydrolyzes to the corresponding acid. Alkaline decarboxylation of the latter gives opsopyrrole-dicarboxylic acid, IVa.
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Macdonald et al. (1955) studied this question.
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