44 触媒的不斉合成を利用した(+)-crinamine、(-)-haemanthidineおよび(+)-pretazettineの全合成(口頭発表の部)
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Transition metals have been playing very important roles in modern synthetic organic chemistry. We succeeded in the first asymmetric total syntheses of (+)-crinamine (1), (-)-haemanthidine (2) and (+)-pretazettine (3) in crinine-type alkaloids, using palladium-catalyzed asymmetric amination, and intramolecular carbonyl-ene reaction as the key steps. Palladium-catalyzed asymmetric amination of 12a with 8 gave (S)-15 with 84% ee in 87% yield. On the other hand, 13a afforded (S)-16 with only 60% ee under the same reaction conditions. The ees of 15 and 16 were slightly increased when the reactions were carried out at 0 ℃, although the starting materials were recovered. However, in the case of enol carbonate 12c and 13c, the reactions proceeded smoothly even at -20℃ because the deprotonation from 9 was accelerated due to the strong basity of counter anion in π-allyl palladium complex II, and 15 with 92% ee, and 16 with 74% ee were obtained. As expected, when a toluene solution of 18 was heated at 230-240℃, the desired intramolecular carbonyl-ene reaction proceeded, and hexahydroindole 20 was obtained in 30-40% yield (conversion yield: 46-60%) as a sole product. On the other hand, SnCl_4-catalyzed (10 mol %) carbonyl-ene reaction of 18 gave an unusual rearrangement product 19a in 89% yield. To synthesize (+)-1, recrystalyzation of 16 with 74% ee gave an optically pure (-)-16 from the mother liquor. Deacetalyzation of 16 following intramolecular carbonyl-ene reaction gave 21. Allylic oxidation of 21 with SeO_2 gave alcohol 22 as a sole product, which was followed by treatment with Ms_2O and then MeOH gave 23 as a major product. Detosylation of 23 followed by methylenation and then deacetylation proceeded smoothly to give (+)-1. Subsequentry, treatment of 25 with HC(OMe)_3 in the presence of Montmorillonite K-10 gave 24 in high yield. Detosylation of 24 followed by formylation gave compound 26, which was treated with POCl_3, followed by deacetylation, gave (-)-2. Using a known method, (+)-3 was synthesized from (-)-2. The [α]_D value, melting point and spectral data of synthetic 2 and 3 agreed with those reported in the literature.
- 天然有機化合物討論会の論文
- 1998-08-31
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