PORPHYRINS WITH EXOCYCLIC RINGS .4. AN IMPROVED ONE-STEP SYNTHESIS OF CYCLOPENTA[B]PYRROLES

Cyclopentanone condensed with phenylhydrazones 5, or oximes 6, in the presence of zinc dust, sodium propionate and propionic acid at 150-degrees to give cyclopenta[b]pyrroles 7 in good yields. This chemistry was extended to the synthesis of pyrrolic products from 1-indanone, 2-indanone and 2-methylcyclopentanone. Benzyl 3-methylcyclopenta[b]pyrrole-2-carboxylate was found to react regioselectively with lead tetraacetate to give the corresponding 6-acetoxy derivative and subsequent acid-catalyzed condensations with 5-unsubstituted pyrrole-2-carboxylates afforded a series of synthetically valuable dipyrroles 18a-c.