Abstract
The synthesis of dl-steporphine (1), an aporphine-type alkaloid having a hydroxyl group at the 4-position, is described. The acetophenone derivative (4), prepared from 2 and 3 by Friedel-Crafts reaction, was condensed with aminoacetaldehyde diethyl acetal to afford the ketimine derivative (5). The product (6), from the sodium borohydride reduction of 5 or its N-methyl derivative (7) was subjected to hydrolytic cyclization in concentrated hydrochloric acid to afford stereospecifically 1-(2-bromobenzyl)-4-hydroxy-6, 7-methylenedioxy-1, 2, 3, 4-tetrahydroisoquinoline (8) or its N-methyl derivative (9), respectively, with a cis relationship between C1-H and C4-H. The stereospecificity is presumed to be due to intramolecular hydrogen bonding between the alcoholic hydroxyl group and the bromo atom. Irradiation of 9 in dilute hydrochloric acid afforded dl-steporphine (1). This is the first stereospecific synthesis of 4-hydroxyaporphine-type alkaloids, and the method should be adaptable to the synthesis of other alkaloids of this type.
