[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.
Treatment of 2-(2'-bromo-beta-phenethyl)isocarbostyrils 7 with AIBN-Bu(3)SnH in boiling benzene gave 8-oxoberbines 3 in good yields. A similar treatment of 2-(2'-bromo-beta-phenethyl)isoquinolinium bromides 6 and their nor- and homoanalogues (10,11) induced 6-, 5-, and 7-exo radical closures in a one-pot manner to give protoberberines 2, dibenzo[b,g]indolizidine 14a and, dibenzo[a, h]-1-azabicyclo[5.4.0]undecane 15a, respectively. A one-pot radical cyclization of 1-(2'-bromobenzyl)isoquinoline methiodide 18a gave a pavine alkaloid, (+/-)-algemonine (19a).
Treatment of 1-(2'-bromobenzyl)-3,4-dihydroisoquinolines 2 in the presence of K(2)CO(3) in boiling DMF efficiently provided a variety of alkoxy-substituted indolo[2,1-a]isoquinolines 3. Application of this cyclization to 7-benzyloxyisoquinoline derivatives, followed by further elaboration of the resultant 2-benzyloxy-5,6-dihydroindolo[2,1-a]isoquinolines 16a,b, led to the formal synthesis of dibenzopyrrocoline alkaloids, (+/-)-cryptaustoline (1a) and (+/-)-cryptowoline (1b).
Phosphane-free Pd 0 -catalyzed intramolecular aromatic amination was studied. o-Halophenethylamines and 3-(o-halophenyl)propylamines were found to be transformed into indolines and quinolines in a catalytic system based on Pd(OAc) 2 and Cu(OAc) 2 in the presence of K 2 CO 3 . Application of the method to substrates containing isoquinoline rings -the 1-(o-bromobenzyl)-3,4-dihydroisoquinolines 6, the 1-(o-bromobenzyl)-1,2,3,4-tetrahydroisoquinolines 7, and the 1-(o-bromophenethyl)isoquinolines 9 -provided the indolo[2,1-a]isoquinoline and dibenzo[a,f]quinolizine ring
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