Lead tetraacetate Oxidation of isoquinolines

Tetrahydro-3-benzazepin-2-ones Lead Tetraacetate Oxidation of Isoquinoline Enamides. 

TETRAHYDRO-3-BENZAZEPIN-2-ONES lead TETRAACETATE OXIDATION OF ISOQUINOLINE ENAMIDES... 

Lenz, G. R. Lessor, R. A. Tetrahydro-3-benzazepin-2-ones Lead Tetraacetate Oxidation of Isoquinoline Enamides OS, (1991), 70, 139. 

Lead Tetraacetate Oxidative Ring Expansion of Isoquinoline Enamides... 

More recently, the preparative value of VOCl3 and VOF3-TFA in chemical oxidation has been demonstrated (see Section III, on the pro-aporphine and promorphinane alkaloids) (415,462). Some other authors used the purified enzyme horseradish peroxidase (463). By this method the aporphine base (besides the quaternary dibenzopyrrocoline) is readily obtained from (S)-( + )-laudanosoline hydrobromide or from (/ )-(—)-laudanosoline methiodide with retention of the absolute configuration. The synthesis of 6a,7-dehydroaporphine bases was also carried out by making use of the benzyne reaction (439). Reduction of these substances affords the corresponding aporphine bases (439). The synthesis of isoquinoline alkaloids by lead tetraacetate oxidation was reviewed by Umezawa and Hoshino (343). 

Ochiai and Ohta have used lead tetraacetate in benzene to convert aromatic iV-oxides (67) to the corresponding acetylated hydroxamic acids (68). Similar oxidation of quinoline and isoquinoline JV-oxides... 

Quinoline 1-oxide undergoes nucleophilic attack by ozone to yield a hydroxamic acid (128), and 40% of the starting iV-oxide is recovered (Scheme 74). When an excess of ozone is employed the aldehydes (129) and (130) are obtained. Formation of these products has been attributed to electrophilic attack by ozone rather than further oxidation of (128), because in a separate experiment (128) yielded carbostyril on treatment with ozone. Isoquinoline 2-oxide yields 2-hydroxyisoquinolin-l-one, and acridine 10-oxide gives 10-hydroxyacridone and acridone in a similar manner to the above. Likewise, phenanthridine 5-oxide affords mainly 5-hydroxyphenanthridone. Quinoline 1-oxide undergoes oxidation by lead tetraacetate as shown (Scheme 75). 

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