13 核間窒素原子を有する二環性アルカロイドの単純化不斉合成(口頭発表の部)

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Recently, we reported the first successful chiral alkylation onto 4-acetoxy-2-azetidinones (3 and 6 employing the tin(II) enolates of C4-chiral-3-acyl-1,3-thiazolidine-2-thiones (1a-d and 12) and its application to the chiral synthesis of 1β-substituted carbapenems (11 and 15). Now, we expanded this chiral tactics to alkaloid syntheses. Chiral alkylation of 5-acetoxy-2-pyrrolidinone (18) or 6-acetoxy-2-piperidone (21) with the tin(II) enolates of 3(ω-chloroalkanoyl)-4(S)-isopropyl-1,3-thia-zolidine-2-thiones(22a-d) furnished the corresponding alkylated products 24a-d in a highly diastereoselective manner (≧93 - ≧97%de) and in 57-73% yields. Subsequent reductive annulation of 24a-d with LiAlH4 at 0℃ and then under reflux gave directly the desired bicyclic products 33a-d in 41-69% yields together with the corresponding hydrogenolysis by-products 34a-d. Compounds 33a (≧99%op) and 33d proved to be (-)-trachelanthamidine and (-)-epilupinine, respectively. Naturally occurring (+)-epilupinine (37)(≧97%op) was similarly synthesized. A unified mechanism 30 for the stereochemical outcome of the chiral alkylation and new empirical aspects (Figure 1) for the reductive annulation toward the N-atom-containing bicyclic compounds are also discussed in the text. Thus, we succeeded in developing an extremely short chiral synthesis of the bicyclic alkaloids involving pyrrolizidine, indolizidine, and quinolizidine skeletons.
天然有機化合物討論会の論文
1987-07-25

13 核間窒素原子を有する二環性アルカロイドの単純化不斉合成(口頭発表の部)

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