title: 3,3'- and 4,4'-Dimethoxy-2,2'-bipyrroles: highly electron-rich model compounds for polypyrrole formation.
abstract: 3,3'-Dimethoxy-2,2'-bipyrrole (1) and 4,4'-dimethoxy-2,2'-bipyrrole (2) were obtained in short sequences and good yields from N-benzyl-3-hydroxypyrrole-2,4-dicarboxylic acid. The key intermediate leading to 1 is an N-benzyl-3-methoxypyrrole, which is dimerized by lithiation and oxidation with NiCl(2). The formation of 2 is achieved by a classical Ullmann coupling of diethyl 1-benzyl-2-bromo-4-methoxypyrrole-3,5-dicarboxylate. The N-benzyl protection groups of 1 and 2 are cleaved under reducing conditions with sodium in liquid ammonia. Both isomeric bipyrroles are extremely sensitive toward air. Compound 1 has a very low oxidation potential of 0.09 V against AgCl but film formation hardly occurs. On the other hand, compound 2 with a potential of 0.35 V readily forms stable polypyrrole films with anodic waves at -0.51 and -0.35 V and a cathodic wave at -0.77 V, the lowest potential ever observed for a p-doped polymer.
authors.affiliation: Institut of Organic Chemistry, University of Regensburg 93040 Regensburg, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Merz
authors.forename: Sergiy
authors.initials: S
authors.lastname: Anikin
authors.forename: Bernd
authors.initials: B
authors.lastname: Lieser
authors.forename: Jürgen
authors.initials: J
authors.lastname: Heinze
authors.forename: Hermann
authors.initials: H
authors.lastname: John