Synthesis of some dibenzo[a,h]quinolizines

Abstract

The oximes of some alkoxy-derivatives of 3,4-dihydro-2-(2-oxoethyl)-1-phenylisoquinolinium halides and the corresponding 1,2,3,4-tetrahydroisoquinolines have been cyclised in warm 6N-hydrochloric acid to give 5,6-dihydrodibenzo[a,h]quinolizinium salts. When these reactions were carried out at room temperature 5,6,8,9-tetrahydro-5-hydroxydibenzo[a,h]quinolizinium compounds and 5,6,8,9-tetrahydro-5-hydroxy-13bH-dibenzo[a,h]-quinolizines were isolated, and shown to undergo subsequent dehydration, accompanied in the latter case by aromatisation.

Reduction of the 5,6-dihydrodibenzo[a,h]quinolizinium salts with sodium borohydride or catalytic hydrogenolysis of the 5,6,8,9-tetrahydro-5-hydroxy-13bH-dibenzo[a,h]quinolizidines gives 5,6,8,9-tetrahydro-13bH-dibenzo[a,h]quinolizines, which probably have the trans stereochemistry at the saturated ring junctions.