モンタニン型ヒガンバナ科アルカロイド, (±) -モンタニン, (±) -コクシニン, (±) -パンクラシンおよび (±) -ブルンスビジンの全合成

抄録

The first stereoselective total syntheses of the montanine-type Amaryllidaceae alkaloids, (±) -montanine 1, (±) -coccinine 2, (±) -pancracine 4, (±) -O- acetylinontanine 5, and (±) -brunsvigine 6 are described. The key steps in the reaction sequences are as follows : (1) stereoselective hydroboration-oxidation of exomethylene by means of an intramolecular charge transfer complex to provide alcohol 44 as a single isomer, (2) cyclization of tosylamide alcohol 49 with vitride® [sodium bis (2-methoxyethoxy) aluminum hydride] to provide functionalized 5, 11-methanomorphanthridine 50, which possesses the basic skeleton of montanine-type alkaloids; and (3) conversion of 56 to allylic chloride 57 a by treatment with PhSeCl in MeOH under ultrasonication followed by NaIO₄ oxidation. A formal total synthesis of (±) -manthine 3 was also achieved.