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.

Abstract

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.