Quinolizidines. XXII. An Extension of the “3-Acetylpyridine Route” to the Syntheses of 9-Hydroxy-10-methoxy- and 10-Hydroxy-9-methoxybenzo [a] quinolizidine-Type Alangium Alkaloids

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Alternative syntheses of the Alangium alkaloids bearing the 9-hydroxy-10-methoxy- and 10-hydroxy-9-methoxybenzo [a] quinolizidine skeletons (types 3 and 4) have now become feasible through generally applicable routes starting from 3-acetylpyridine. The routes include the mercuric acetate-edetic acid oxidation of the 3-acetylpyridine derivatives 8a, b or the alkaline ferricyanide oxidation of the quaternary salts (29a, b and 30a) of 3-acetylpyridine equivalents, Wolff-Kishner reduction of the acetyl group or reductive desulfurization of the thioketal group, sulfenylation dehydrosulfenylation of the lactams 15a, b, Michael reaction of the α, β-unsaturated lactams 18a, b, and hydrolysis, decarboxylation, and esterification of the Michael adducts to give 21a, b, as the main operations.