Aryl Radical Cyclizations of 1-(2‘-Bromobenzyl)isoquinolines with AIBN−Bu₃SnH:  Formation of Aporphines and Indolo[2,1-<i>a</i>]isoquinolines

Abstract

[reaction: see text] Radical cyclization of alkoxy-substituted 1-(2'-bromobenzyl)-3,4-dihydroisoquinolines 1 with AIBN-Bu3SnH gave 6a,7-dehydroaporphines 2 preferentially. A steric repulsion between the respective alkoxy groups at the 7- and 3'-positions gave 5,6-dihydroindolo[2,1-a]isoquinolines 3 in a "disfavored" 5-endo cyclization mode. Radical cyclizations of the related substrates, such as 1-(2'-bromobenzoyl)isoquinolines or 1-(2'-bromo-alpha-hydroxybenzyl)isoquinolines, were also found to give the corresponding oxoaporphines or oxyaporphines.