Dipyrrolic intermediates incorporating five-membered carbocyclic rings are easily prepared from cyclopenta [b] pyrroles, and this unit represents the southern half of the DPEP-type geoporphyrins found in organic-rich sediments such as oil shales and petroleum. Related dipyrroles with six-, seven-or eight-membered carbocyclic rings were shown to give b- bilenes when reacted with dipyrrylmethane carbaldehydes under mildly acidic conditions. ...
