[1,4]Benzodioxino[2,3-g]isoquinolines and [1,4]Dioxinodiisoquinolines

Abstract

Examples of the new ring systems [1,4]benzodioxino[2,3-g]isoquinoline, [1,4]dioxino[2,3-g:5,6-g?]di-isoquinoline and [1,4]dioxino[2,3-g:6,5- g?]diisoquinoline have been prepared. A route starting with chloromethylation of dibenzo[b,e][1,4]dioxin (1a) yielded a reduced tetracyclic derivative (2b) and mixed isomeric reduced pentacyclic derivatives (3b) and (4b). The latter differed in the p.m.r. resonances arising from the protons in positions 5, 7, 12 and 14. Initial di- chloromethylation of (1a) had thus occurred in both the 2,7- and 2,8- positions, whereas acylation normally gives only 2,7-disubstitution. The pentacyclic compound (3b) was prepared unambiguously from 2,7- dimethyl-dibenzo[b,e][1,4]dioxin. A low yield of the fully aromatized tetracyclic compound (2) was obtained by Pictet-Gams cyclization of N- {2-(dibenzo[b,e][1,4]dioxin-2-yl)-2-hydroxyethyl}benzamide.