Trends in heterocyclic chemistry. 4:1-12




Methods have been systematized for preparing substituted 8-quinolinols. The 5 and 7 positions are those available for electrophilic substitution. The entry position of the electrophile can be controlled by controlling the prototropic form of the 8-quinolinol. Under acidic conditions the 5 position is attacked first and under basic conditions the electrophile is directed to the 7 position. Iodination is the reverse. Regiospecificity also can be achieved by blocking the 5 or 7 position with sulfonic acid groups followed by addition of the electrophile and deblocking by acid hydrolysis, providing the new substituent is stable to acid hydrolysis. When compounds containing mixed substituents including bromine or iodine are desired, the more electronegative one must be in place prior to addition of the less electronegative one, to avoid Reverdin rearrangements. For 3- and 3 ,6-dihalo-8-quinolinols, 8-nitroquinoline can be halogenated, reduced to amino and hydrolyzed to the substituted 8-quinolinol. Proton nmr allowed ready detection of rearrangements involving nitro groups

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