Stereochemistry and X-ray Crystal Structure of$lsquoPyrrole Trimer’: Synthesis ofcis-2,5-Di(pyrrol-2-yl)pyrrolidine (cis PyrroleTrimer) and X-ray Crystal Structure ofcis-1-(4-Methylphenylsulfonyl)-2,5-di(pyrrol-2-yl)pyrrolidine (Monotosyl cis Pyrrole Trimer)

Pyrrole reacts with aqueous hydrochloric acid at 0 °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 $lsquopyrrole trimer$rsquo.