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A Knorr cyclization between ethyl a--aminoacetoacetate (prepared in situ) and a 3-alkyl-2,4-pentandione was selected for the preparation of ethyl alkylpyrrole-2 carboxylate derivatives 4b-f, i. Ethyl 3,5-dimethyl-4-tertbutylpyrrole-2-carboxylate 4g was prepared from ethyl 3,5-dimethylpyrrole-2-carboxylate 4a in an alkylation with tert-butyl acetate. In a modification of a Knoevenagel condensation of ethyl N-(3-oxo-1-alkenyl)aminoacetates to ethylpyrrole-2-carboxylates ethyl 3-methyl-2,4,-5,6-tetrahydrocyclopenta[c]pyrrolecarboxylate 4j was obtained by a base catalyzed cyclization of an unisolated enamine 13 (Table IV), in turn obtained from a condensation between glycine ethyl ester and α-acetylcyclopentanone.

1. customwas obtained by a base