43 リコリン及び関連アルカロイドの全合成

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There have been many reports aiming at synthesis of lycorine 41 which is the most wide-spread and common alkaloid occurring in Amaryllidaceae plants. In connection with our synthetic work of Amaryllidaceae alkaloids, we have now completed synthesis of lycorine. Treatment of the kown uethane-ester 14 with POCl_3 followed by SnCl_4 in CH_2Cl_2 gave the lactam 12 which was reduced to the alcohol 18. 18 was converted to the chloride 19, then cyclized into the tetracyclic lactam 21 via imino-ether 20. 21 was also obtained from the imide 17, which in turn was obtained from 12 via the acid 16 by reduction with LAH under strictly controlled condition in 80% yield. Oxidation of 21 with m-CPBA gave the α-epoxide 31 as a sole product. Ample supply of the lactam 21 and the epoxide 31 were provided from dihydrolycorine as shown in the text(28→29→30→32→21). The α-epoxide 31 on treatment with 5% H_2SO_4 in dioxane afforded the trans-diol 29 which regenerated dihydrolycorine 28 by LAH reduction. Osmolation of the lactam 21 gave the cis-glycol 34 which was converted to zephyranthine 35. Treatment of the epoxide 31 with diphenyldiselenide and NaBH_4 followed by oxidation with NaIO_4 resulted in 38 (isocaranine-lactam). Acetylation of 38 gave the acetate which was oxidized with m-CPBA to give the β-epoxide 39. Treatment of 39 with diphenyldiselenide and NaBH_4 followed by NaIO_4 in the same manner as the case of 31 furnished lycorine-lactam 40. Reduction of its diacetate with LAH gave lycorine 41.
1975-10-01

43 リコリン及び関連アルカロイドの全合成

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