Simplified Analogues of Lysergic Acid. IV. Synthesis of 1-Methyl-1,2,3,7,8,9,-hexahydro-5,6-benzquinoline

Abstract

The lysergic acid analogue 1-methyl-1,2,3,7,8,9-hexahydro-5,6-benzquinoline (III ; R=H) was prepared from 2-bromo-α-tetralone by two parallel routes. The first, a seven-stage sequence, involved conversion of the starting material into 2-[N-methyl-N- (2'-oxo-n-propyl)]-amino-α-tetralone (IX) via its ethylene ketal, followed by ring closure to the tricyclic 1-methyl-3-oxo-1,2,3,7,8,9-hexahydro-5,6-benzquinoline (V). This was transformed into its ethylene dithioketal (XXIX) and thence by desulphurization into (III: R=H). The second pathway, a five-step synthesis, utilized dimethylaminoacetone to obtain directly the quaternary diketone (XXI), which was cyclized to 1,1-dimethyl-3-oxo-1,2,3,7,8,9-hexahydro-5,6-benzquinolinium bromide (XXV), identical with that obtained by the alternative route.