Studies on the syntheses of heterocyclic compounds. Part 673. New routes to benzo[a]quinolizines

Abstract

Heating 3,4-dihydro-6,7-dimethoxy-1-methylisoquinoline (1) with crotonic anhydride (2) gave 3,4,6,7-tetrahydro-9,10-dimethoxy-4-methylbenzo[a]quinolizin-2-one (5) along with 2-crotonoyl-1,2,3,4-tetrahydro-6,7-dimethoxy-1-methyleneisoquinoline (3) and N-(2-acetyl-4,5-dimethoxyphenethyl)crotonamide (4). Heating the isoquinoline (1) with glutaconic anhydride (17) in pyridine provided 1,6,7,11b-tetrahydro-9,10-dimethoxy-11b-methylbenzo[a]quinolizin-4-one (19).