Reactions of 3,3′-Linked Bispyrroles with Carbon Electrophiles

The reactivity of 3,3 '-linked bispyrroles, easily accessible by ring-enlargement reactions of donor-acceptor cyclopropanes, towards various carbon electrophiles was investigated. A biscyclopropanated furan, equipped with imines as acceptor units, was converted by rearrangement and subsequent elimination of water to 3,3 '-linked bispyrroles. Thereby the nucleophilic 2-position of the pyrroles stayed unsubstituted, thus permitting a further reaction with electrophiles. The heterocycles were treated with oxalyl chloride to form a new six-membered ring between the pyrrolic subunits. The 1,2-diketone moiety in these species was used as a starting point to extend the pi-system via a condensation reaction with aromatic 1,2-diamines. The reaction of 3,3 '-linked bispyrroles with the phosgene surrogate triphosgene led to a seven-membered anhydride. The use of the Vilsmeier reagent led to a formylation of the bispyrroles. Furthermore, a direct oxidative coupling between two bispyrroles resulted in a previously unknown linkage (3,3 ':2 ',2 '':3 '',3 ''') between four pyrrole subunits.