In a previous work, kainic acid and its derivatives were synthesized from 3-carboxymethyl-4-acetyl-2-pyrrolidinecarboxylic acid (the methyl ketone compound of kainic acid). In order to complete the total synthesis of these compounds, an attempt to synthesize the methyl ketone compound was made. Oxidative cleavage of cis-2-benzoyl-4-methyl-tetrahydro-4H-cyclopenta [c] pyrrol-5 (6H)-one (III) with potassium permanganate afforded trans-4-acetyl-3-pyrrolidineacetic acid (VI) (the 2-decarboxy-methyl ketone compound).
So, in order to synthesize the methyl ketone compound of kainic acid, a compound possessing a carboxyl group in 1-position of III was prepared. The route shown in Chart 1 failed to give the cyclized pyrrolidine compound, cis-3a, 4, 7, 7a-tetrahydro-1-isoindolinecarboxylic acid (XV), but XV was obtained by the route starting with XII and via the cyanohydrin compound (XVII).
