Quinoline alkaloids. Part XIV. Asymmetric synthesis by the peroxy-acid–olefin reaction. The absolute stereochemistry of balfourodine, isobalfourodine, and related compounds, and the biosynthesis of isomeric dihydrofuro- and dihydropyrano-derivatives
Reactions of 3-(3-methylbut-2-enyl)-2,4-dihydroxyquinoline derivatives with (+)- and (–)-peroxycamphoric acid, with (+)- and (–)-peroxyhydratropic acid, and with (+) and (–)-norbornane-2-endo-peroxycarboxylic acid furnished optically active dihydrofuroquinoline alkaloids, balfourodine and O-methylbalfourodinium salt, and the dihydropyranoquinoline, isobalfourodine (2–10% optical induction). The absolute stereochemistry of the alkaloids was determined by ozonolysis to 3-hydroxy-4,4-dimethyl-γ-butyrolactone. The stereochemical results are discussed in relation to the peroxy-acid-olefin reaction, to the balfourodine–isobalfourodine rearrangement, and to the biosynthesis of coumarins and quinolines containing hydroxyisopropyldihydrofuran and hydroxy-dimethyldihydropyran rings.