45 エリスリナアルカロイドの合成研究 : Erysotramidine,3-Epierysotramidine 3-Epi-8-oxoerythralineの合成
詳細
An efficient synthesis of Erythrina alkaloid was described. 1. Synthesis of isoquinolinopyrrolinedione 5. The synthesis of 5 was achieved starting from arylethylamine 6 in yield of 60〜80% by following three steps: i) Condensation with ethyl or methyl malonyl chloride. ii) Intramolecularcyclization to isoquinoline. iii) Condensation with oxalyl chloride. 2. Diels-Alder Reaction of 5 with butadienes. Diels-Alder addition of 5 with butadienes, specially 1-methoxy-3-silyloxybutadiene or 1,3-disilyloxybutadiene, smoothly proceeded in a regio and stereospecific manner to give 1,4-adducts 12 and 13, respectively, having an erythrinan skelton. The structures were elucidated by the X-ray analysis of the diacetate 20 derived from 12c. 3. Syntheses of erysotramidine 2,3-epierysotramidine 28, 8-oxoerythraline 35 and 3-epi-8-oxoerythraline 34. The value of this approach to Erythrina alkaloid was demonstrated by the total synthesis of 2 and its epimer 28. Partial reduction of 12b or 13b with LiBH_4, followed by acidic treatment afforded a conjugated ketone 22. Decarboalkoxylation of 22 with MgCl_2 in DMSO gave a dienone 24. Reduction of this with NaBH_4 gave epimeric allyl alcohols 25 and 26, which on methylation with CH_3I furnished 3-epierysotramidine 28 and erysotramidine 2, respectively. 8-Oxoerythraline 35 and its 3-epimer 34 were also synthesized from the key intermediate 13c by similar procedure.
