Synthesis of trisubstituted C 18 pyrrole fatty ester derivatives

Reaction of methyl 10(11)‐dicarbethoxymethyl‐9,12‐dioxooctadecanoate (1a,1b) with ammonium acetate furnished a mixture of positional isomers of a pyrrole derivative, methyl 9,12‐imino‐10(11)‐dicarbethoxymethyl‐9,11‐octadecadienoate (2a,2b). Decarboxylation of the mixture of compounds 2a,2b with sodium carbonate in aqueous methanol yielded a mixture of compounds 3a,3b containing a CH 2 COOCH 3 group at the 3‐ or 4‐position of the pyrrole ring after esterification. Heating of the hydrolyzed mixture of compounds 3a,3b at 180°C for 1 h gave the desired trisubstituted pyrrole derivatives, methyl 9,12‐imino‐10(11)‐methyl‐9,11‐octadecadienoate (4a,4b), containing a methyl group at the 3‐ or 4‐position of the pyrrole nucleus. The structures of the products and intermediates were confirmed by infrared, and by 1 H and 13 C nuclear magnetic resonance spectroscopy.