Lead Tetraacetate Mediated Oxidation of the Enamides Derived from 1-Benzyl-3,4-dihydroisoquinolines

Article abstract of DOI:10.1021/jo00241a011

The products obtained from the lead tetraacetate (LTA) oxidation of N-acylbenzylidene isoquinoline enamides are a function of the type of carbonyl function in the enamide, the solvent,and the type of substitution on the benzylidene aromatic ring.The benzoyl enamides yield Z-β-acethoxy-substituted enamides.The ethoxycarbonyl enamides, containing electron-releasing substituents on the benzylidene ring, efficiently form oxazolones when oxidized with LTA in acetic acid.In the absence of electron-releasing substituents, ring opening occurs to form benzoin esters.When the same oxidation is conducted in benzene, the enamide double bond is converted into its diacetoxy derivative, which can undergo a variety of reactions.LTA oxidation of acetyl enamides results in cleavage of the acetyl group with ultimate formation of 1-benzoyl-3,4-dihydroisoquinolines and isoquinolines.Oxidation of the formyl enamide with LTA results in cleavage of the formyl group with formation of a variety of products.Most of these have an acetyl group in place of the original formyl and are the result of either cleavage of the benzylidene ring at the double bond, oxidation, and subsequent ring opening to a benzil or various other oxidative and rearrangement processes.