An Expedient Route to 2,3-Substituted and Fused Benzo[<i>a</i>]quinolizine-4-thione Framework via Ring Annulation with <i>β</i>-Oxodithioesters

Abstract

[figure: see text] An efficient highly convergent route to hitherto unreported 2,3-substituted and annulated benzo[a]quinolizine-4-thiones 3 has been developed. The methodology involves ring annulation of 3,4-dihydro-6,7-dimethoxy-1-methylisoquinoline 1 with a variety of readily accessible acyclic and cyclic beta-oxodithioesters 2 in the presence of triethylamine in refluxing benzene. These benzo[a]quinolizine-4-thiones can be readily converted to the corresponding benzo[a]quinolizine-4-ones 5 via dethiomethylative hydrolysis of the respective benzo[a]quinolizinium salts 4 obtained by alkylation of 3 with methyl iodide.