57 四級炭素の不斉構築 : テルペノイドの全合成への応用(口頭発表の部)

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Recently, we have developed a new method for the construction of chiral quaternary carbon centers using the chiral nitroenamine 1, which has a SMP group as a chiral leaving group. The reactions of the chiral nitroenamines with zinc enolate of α-alkylated-δ-lactones afforded optical active nitroolefinlactones 3 in high yields with high enantiomeric excess. This reaction proceeds through the addition-elimination process. Addition of enolates to 1 occurs through the six-membered ring transition state including metal cation under kinetic control (Scheme 1). As an application to the total syntheses of naturally occuring terpenoids, the synthesis of (+)-podocarpic acid (5) was accomplished in nine steps starting from (S)-nitroolefinlactone 3a. The conjugate addition of the Grignard reagent to nitroolefin, ring A construction by the intramolecular alkylation of nitroalkane, and stereoselective ring B construction are included as key reactions. This synthesis constitutes the formal asymmetric syntheses of six diterpenoids (taxodione, nagilactone, callitricic acid, hinokino methylether, trachiloban-19-oic acid, and lambertianic acid), which have been transformed from (+)-podocarpic acid. Starting from (R)-nitroolefinlactone, an optically active tricyclic compound 6 was synthesized by the same synthetic method. This synthesis also constitute the formal asymmetric syntheses of three diterpenes okaurenoic acid, steviol. and monogynol) and three diterpene alkaloids (acisine, veachine, and garryine).
天然有機化合物討論会の論文
1988-09-26

57 四級炭素の不斉構築 : テルペノイドの全合成への応用(口頭発表の部)

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