Total Synthesis of Pyrrolnitrin. III. Synthesis of Ethyl 3-Aryl-5-methyl-2-pyrrolecarboxylate. (2)

Cyclization of diethyl N-[1-methyl-3-(2-nitro-3- chlorophenyl)-3-oxopropylidene]-aminomalonate (XV) with polyphosphoric acid ethyl ester (PPE) gave ethyl 3-(2-nitro-3-chlorophenyl-5-methyl-2-pyrrolecarboxylate (XVI) in good yield. In such reaction, diethyl 3-(3-chlorophenyl)-5-methyl-2, 2-(2H)-pyrroledicarboxylate (XX) was obtained easily by ring-close of diethyl N-[1-methyl-3-(3-chlorophenyl)-3-oxopropylidene] aminomalonate (XVIII) with PPE. It may be concluded from this result that ethyl 3-aryl-5-methyl-2-pyrrolecarboxylate was prepared via the 2H-pyrrole compound from the corresponding enamine.