A General Route to 1,3′-Bipyrroles

A general method is described for the synthesis of 1,3′-bipyrroles. The route involves constructing a pyrrole ring on the nitrogen of a substituted 1H-pyrrole, so as to generate the 1,3′-bipyrrole. In this approach the nitrogen of the starting pyrrole was alkylated with a special Michael acceptor having an allylic leaving group, and the product was then modified in such a way that the second pyrrole ring could be formed by a Paal–Knorr reaction. Two variants of this sequence were examined, one of which led to formation of a 3-hydroxypyridine instead of the second pyrrole ring; the other variant used phenacyl bromide instead of the special Michael acceptor.