64 付加・脱離型不斉誘導 : ラクトン類の不斉ニトロオレフィン化を利用する光学活性インドールアルカロイドの全合成

概要

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A new method for a chiral synthesis of quaternary carbon centers through the addition-elimination process using a chiral leaving group was developed. It was applied to the enantio-selective synthesis of Aspidosperma alkaloids. The chiral nitro enamine 1a, which has a chiral auxiliary derived from (S)-proline, reacted with various enolates 4-12 to afford optically active nitroolefins via addition-elimination process. α-Substituted δ-lactone enolates 10-12 showed the best results in termes of chemical yield and enantiomeric excess. This method was successfully extended to substituted nitro enamines 1b and 1c to furnish the corresponding nitroolefin with high ee's in good chemical yield. Generally, enantiomeric selection was more effective with Zn^<2+> than Li^+ as a counter cation. Enantioselective total syntheses of (+)-quebracamine and (-)-aspidospermidine have been accomplished starting from chiral nitroolefin 14.
天然有機化合物討論会の論文
1986-09-09