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

Abstract

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 π‐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.