103(P30) 光学活性α,β-エポキシケトンの転位反応を用いる天然物合成(ポスター発表の部)

概要

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The construction of a chiral building block with a quaternary carbon center has been developed in our laboratory, based on the Lewis acid catalized acyl migration of α,β-epoxy ketone with alkyl substituents. As a further extention of this studies, we now investigated an application of this methodology for the asymmetric synthesis of natural products, such as (-)-aspidospermidine 4 and (+)-asteltoxin 5. As illustrated in our retrosynthetic analysis of aspidospermidine 4 (Scheme 1), we employed a condensation reaction of oxytryptamine with C9-lactone-unit 17, prepared from chiral α,β-epoxy ketone 11 in 11 steps, and the resulting mixture was followed by oxidation with TPAP-NMO to give four stereoisomers of 19a-d. 19a,c were successfully transformed into a pentacyclic compound 21, a known synthetic intermediate of aspidospermidine. We also studied an additional example for the synthesis of asteltoxin 5 from another chiral epoxy ketone 26 as sununerized in Scheme 5. Triol 27 was easily transformed into tetrahydrofuran derivative 34 in 12 steps, which involves a stereoselective lactonization as a key step. Conversion from 34 into cis-diol 35a was achived stereoselectively by treatment with OsO_4 in aq. acetone. The stereochemistry of 35a was confirmed by leading to bis-tetrahydrofuran derivative 36 in high yield. Further transformation from 35a into (+)-alteltoxin is in progress.
天然有機化合物討論会の論文
1996-09-02