Synthetic studies on pyrroloquinolines. Part 5. Preparation of hydrogenated 3a-methylpyrrolo[2, 3-b]quinolines

Abstract

Dissolving-metal reduction of 3-(2-aminoethyl)-1,3-dimethyl-2 (1H)-quinolone (7a), derived from 7-chloro-1,3-dihydro-1, 3-dimethyl-3-(2-phthalimidoethyi)quinoline-2, 4-dione (3a) by catalytic hydrogenation followed by removal of the phthaloyl group yielded 2, 3, 3a, 4, 9, 9a-hexahydro-3a, 9-dimethyl-1H-pyrrolo[2, 3-b]quinoline (8a) together with 3-methyl-3-(o-methylaminobenzyl)-2-pyrrolidone (9). The latter compound produced sting material (7a) on treatment with dilute acid. The stereochemistry of the B–C ring junction of the 6-methgxy-analogue of (8a) was found to be cis by X-ray analysis. A facile synthesis of 2, 3, 3a, 4, 9, 9a-hexahydro-6-methoxy-1, 3a-9-trimethyl-1H-pyrrolo[2, 3-b]quinoline (13) has been devised.