Porphyrins with exocyclic rings. Part 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° 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‐unsubsti‐tuted pyrrole‐2‐carboxylates afforded a series of synthetically valuable dipyrroles 18a‐c.