The synthesis of both antipodes of N-methyl-N-[(Z)-styryl]-3-phenyloxirane-2-carboxamide (SB204900), clausenamide, neoclausenamide, homoclausenamide and ζ-clausenamide have been accomplished using (2S,3R)- and (2R,3S)-3-phenyloxirane-2-carboxamides as the starting materials, and SB204900 was found to be a common precursor to other N-heterocyclic clausena alkaloids. Mediated by Brønsted acids under different conditions, for example, SB204900 underwent efficient and diverse alkene-epoxide cyclization, enamide-epoxide cyclization and arene-epoxide cyclization reactions to produce the five-membered N-heterocyclic neoclausenamide, its 6-epimer, the six-membered N-heterocyclic homoclausenamide and the eight-membered N-heterocyclic ζ-clausenamide, respectively, in good to excellent yields. Regiospecific oxidation of neoclausenamide and its 6-epimer afforded neoclausenamidone. Enolization of neoclausenamidone in the presence of LiOH and the subsequent protonation under kinetic conditions at â78 °C led to the epimerization of neoclausenamidone into clausenamidone. Reduction of clausenamidone using NaBH4 furnished clausenamide in high yield.
以(2S. 3R)-和(2R,3S)-3-
苯基
环氧乙烷-
2-甲酰胺为起始原料,合成了 N-
甲基-N-[(Z)-
苯乙烯基]-3-
苯基
环氧乙烷-
2-甲酰胺 (
SB204900)、克劳森
酰胺、新克劳森
酰胺、同克劳森
酰胺和 δ-克劳森
酰胺的两个对位物、发现
SB204900 是其他 N-杂环克劳塞纳
生物碱的常见前体。例如,在不同条件下由布氏酸介导,
SB204900发生了高效、多样的
烯-
环氧化物环化反应、
烯酰胺-
环氧化物环化反应和炔-
环氧化物环化反应,分别生成了五元N-杂环新
氯森
酰胺、其6-表聚体、六元N-杂环同
氯森
酰胺和八元N-杂环δ-
氯森
酰胺,收率从良好到极佳。新
氯森
酰胺及其 6-epimer 的 Regiospecific
氧化反应生成了新
氯森
酰胺酮。新
氯硒脒
酮在 LiOH 存在下发生
烯醇化反应,随后在 °78 °C的动力学条件下发生质子化反应,从而使新
氯硒脒
酮发生表聚反应,生成克劳
硒脒
酮。用 NaBH4 还原克劳
烯酰胺酮,可以得到高产率的克劳
烯酰胺。