Synthetic studies on pyrroloquinolines. Part IV. Preparation hydrogenated 3a-methylpyrrolo[3,2-c]quinolines

Abstract

Removal of the phthaloyl group from 7-chloro-3-methyl-3-(2-phthalimidoethyl)quinoline-2,4-dione (2) followed by cyclization gave 7-chloro-3,5-dihydro-3a-methyl-2H-pyrrolo[3,2-c]quinolin-4-(3aH)-one (3), the CN bond of which was reduced stereospecifically to give the 3a,9b-trans-compound (4) with sodium borohydride at –30 to –20°. Although treatment of compound (4) with lithium aluminium hydride mainly afforded the abnormal reduction product, 7-chloro-3,3a,4,5-tetrahydro-3a-methyl-2H-pyrrolo[3,2-c]quinoline (7), treatment with aluminium hydride simply reduced the oxo-group to give the trans-hexahydropyrroloquinoline (9). The cis-isomer (10) was obtained, along with the trans-isomer (9), by reduction of compound (7) with sodium borohydride.