Synthesis of Polyhydroxylated Pyrrolizidine Alkaloids of the Alexine Family by Tandem Ring-Closing Metathesis−Transannular Cyclization. (+)-Australine
作者:James D. White、Peter Hrnciar
DOI:10.1021/jo0012748
日期:2000.12.1
9 via oxazolidinones 15 and 51, respectively, underwent ring-closing metathesis with Grubbs's catalyst to give azacyclooctenes 26 and 55. Treatment of each azacyclooctene with m-chloroperoxybenzoic acid afforded beta-epoxide 28 from 26 and alpha-epoxide 61 from 60. Basic hydrolysis of each of these oxazolidinones was accompanied by transannular attack at the epoxide by nitrogen, resulting in 2-(O-b
由环氧醇9分别经由恶唑烷酮15和51制备的二烯23和54,用Grubbs的催化剂进行闭环易位,得到氮杂环辛烯26和55。用间氯过氧苯甲酸处理每种氮杂环辛烯得到26和26的β-环氧化物28。 60的α-环氧化物61。每一种恶唑烷酮的碱性水解都伴随着氮对环氧化物的环过环进攻,从而产生2-(O-苄基)-7-脱氧阿瑞辛(29)和1,2-二-(O -苄基)australine(62)。后者在氢解后转化为生物碱澳大林碱(3)。尝试实现二烯37、38和46的闭环易位的尝试失败,这表明,尽管Grubbs的催化剂可以耐受一个烯丙基氧取代基,但两个不能。