Isoquinoline 2-oxide, bromination

Although, in most cases, iodine is a fairly inert halogen (in contrast to bromine) and does not normally react with the substances that have been chromatographed there are, nevertheless, examples where chemical changes have been observed. Oxidations can evidently take place (e.g. aromatic hydrocarbons and isoquinoline alkaloids [252,253]) and additions and substitutions have also been observed. Pale zones then appear on a brown background. 

Isoquinoline 2-oxide was converted by bromine in acetic anhydride in the presence of sodium acetate into the 4-bromo 2-oxide, presumably via an addition-elimination process (84MI2). Metallic derivatives have been used occasionally to prepare bromoisoquinolines, as in the formaton of 79, a process accompanied by ring-opening [87JCS(PI)1865]. 

In a reinvestigation of earlier work (33LA(505)103) by Diels and Alder, Acheson et al. (60JCS1691) established that the stable isomer obtained by addition of two moles of dimethyl acetylenedicarboxylate to one of pyridine was the 4/7-quinolizine (96) and that this with bromine was oxidized to a quinolizinium salt (97 Scheme 65). 4iT-Quinolizines obtained from isoquinoline (62JCS748) and phenanthridine (63JCS3888) were similarly aromatized to afford benzo[a]quinolizinium (98) and dibenzo[a,c]quinolizinium ions (99) respectively. 

Quinoline 1-oxide gives a 4-bromo derivative (Br2-H20,100°C). Isoquinoline 2-oxide is brominated in the 4-position by the mechanism of Scheme 13. 

Bromination and nitration of some annulated thieno[3,2-6]pyridines were investigated. The reaction of thieno[3,2-c]isoquinoline A-oxide (181) with bromine yields 2,3-disubstituted product 182, whereas treatment of 181 with HN03 affords 2-nitro derivative 183 (1989CS305, 1989CS309). 

Quinoline A -oxide gives a 4-bromo derivative (Br2H20, 100 C). Isoquinoline A -oxide is brominated at the 4-position... 

Anodic oxidation of l-(3, 4 -dimethoxybenzyl)-6,7-dimethoxy-isoquinolines at platinum anodes in acetonitrile affords morphinandienones with the flavinan-tine orientation of substituents (148). Attempts to obtain the isomeric 3,4,6-substitution pattern of salutaridine by use of 6 -bromo-compounds failed, the bromine atom being removed, and 6 -chloro-compounds suffered cleavage. ... 

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