Construction of mononitrogen heterocycles with a combined system of 1-azaspiro[4.n]alkene and 3-benzazocine fragments through the intramolecular eight-membered Heck cyclization
作者:N. Yu. Kuznetsov、V. N. Khrustalev、Yu. N. Bubnov
DOI:10.1007/s11172-010-0252-7
日期:2010.7
Amides, obtained from 1-azaspiro[4.n]alkenes (n = 3, 4, 5) and 2-(6-bromo-1,3-benzo-dioxol-5-yl)acetyl chloride, upon heating with a Herrmann—Beller palladium catalyst undergo intramolecular cyclization by the Heck reaction to form pentacyclic compounds (up to 94% yield) including an 1-azaspiro[4.n]alkene (n = 4, 5) fragment and a new eight-membered 3-benzazocine ring. The structure of the thus obtained pentacycles with the 1-azaspiro[4.4]non-7-ene fragment is isomeric to the structure of the main core of alkaloid cephalotaxine. In the case of 1-azaspiro[4.5]dec-2-ene derivative, the reaction is accompanied by the reduction of bromo amide, with the yield of the cyclization product being 34%. The starting 1-azaspiro-[4.n]alkenes (n = 3, 4, 5) were synthesized by the reductive diallylboration of 3-chloropropion-itrile or the corresponding lactams (piperidin-2-one, (2S)-2-hydroxymethyl-and 5,5-di-methylpyrrolidin-2-one) with subsequent intramolecular metathesis upon the action of Grubbs catalyst.
由1-氮杂螺[4.n]烷基烯(n=3, 4, 5)和2-(6-溴-1,3-苯并二噁烷-5-基)乙酰氯获得的酰胺在赫尔曼-贝勒钯催化剂作用下加热,通过 Heck 反应发生分子内环化,形成含有1-氮杂螺[4.n]烷基烯(n=4, 5)片段和新形成的八元3-苯并氮杂环化合物(产率高达94%)的五元环化合物。因此获得的具有1-氮杂螺[4.4]壬-7-烯片段的五元环结构的异构体与生物碱粗榧碱的主要核心结构相同。在1-氮杂螺[4.5]癸-2-烯衍生物的情况下,反应伴随着溴酰胺的还原,环化产物的产率为34%。起始的1-氮杂螺-[4.n]烷基烯(n=3, 4, 5)是通过烯丙基硼烷还原3-氯丙腈或相应的内酰胺(哌啶-2-酮、(2S)-2-羟甲基和5,5-二甲基吡咯啉-2-酮)并在Grubbs催化剂作用下发生分子内复分解反应合成的。