Stereochemistry and X-ray crystal structure of 'pyrrole trimer': Synthesis of cis-2,5-di(pyrrol-2-yl)pyrrolidine (cis pyrrole trimer) and X-ray crystal structure of cis-1-(4-methylphenylsulfonyl)-2,5-di(pyrrol-2-yl)pyrrolidine (monotosyl cis pyrrole trimer)

Pyrrole reacts with aqueous hydrochloric acid at 0 degrees C to give a 2:1 mixture of trans(1) and cis(2) isomers of 2,5-di(pyrrol-2-yl)pyrrolidine which, by conversion into a mixture of the corresponding monotosyl derivatives then exposure of these to sodium hydroxide under phase-transfer conditions, are converted completely into the tosyl derivative (4) of the cis isomer, from which the tosyl group can be cleaved to produce pure cis 'pyrrole trimer'.