Alkaloid (7aS)-1-methylenehexahydro-1H-pyrrolizine was synthesized from N-diphenylmethyl-(S)-proline ethyl ester by cyclopropanation of the ester group with ethylmagnesium bromide in the presence of titanium tetraisopropoxide, replacement of the protecting group on the nitrogen atom, and cationic cyclopropylallyl isomerization of (S)-1-(1-ethoxycarbonylpyrrolidin-2-yl)cyclopropyl sulfonate into the corresponding allyl bromide. Stereoselective reduction of (7aS)-1-methylenehexahydro-1H-pyrrolizine with sodium tetrahydridoborate in the presence of nickel chloride afforded (−)-heliotridane [(1S,7aS]-1-methylhexahydro-1H-pyrrolizine] in high yield.
生物碱(7aS)-1-亚甲基六氢-1H-
吡咯啉是通过N-二苯甲基-(S)-脯
氨酸
乙酯与
氯化镍存在下的
乙基溴化镁进行
环丙烷化反应合成的,随后在氮原子上替换保护基团,以及对(S)-1-(1-乙氧基羧基
吡咯烷-2-基)环
丙基磺酸酯进行阳离子环丙基烯丙基异构化反应,得到相应的烯丙基
溴化物。采用四氢
硼钠在
氯化镍的存在下选择性还原(7aS)-1-亚甲基六氢-1H-
吡咯啉,最终高收率地获得了(−)-海灯草烷[(1S,7aS]-1-甲基六氢-1H-
吡咯啉]。