作者:Wolfgang G. Wirschun、Yaseen A. Al-Soud、Konstanze A. Nusser、Olli Orama、Gerd-Michael Maier、Johannes C. Jochims
DOI:10.1039/b006525k
日期:——
1-Aza-2-azoniaallene salts 3 react with ethene, and mono- to trisubstituted electron-rich alkenes under mild conditions to afford 4,5-dihydro-3H-pyrazolium salts 4. These cycloadditions proceed with complete Markovnikov regioselectivity and retention of the configuration of the alkene. Reactions of salts 3 with norbornene afford cycloadducts without rearrangement of the norbornane moiety. According to these observations, reactions of heteroallenes 3 with alkenes are mechanistically concerted ‘reverse electron-demand 1,3-dipolar cycloadditions’. In solution 4,5-dihydro-3H-pyrazolium salts 4 with a hydrogen atom in the 5-position tautomerize to 4,5-dihydro-1H-pyrazolium salts 6. A ‘general Wagner–Meerwein rearrangement’ to the 1H-isomer 5y is observed for compound 4y. The mechanistic proposals are supported by AM1 calculations. For the salt 4r and the twofold cycloadduct 4z X-ray stuctural analyses have been performed.
1-氮杂-2-氮杂联烯盐 3 与乙烯以及单取代至三取代的富电子烯烃在温和条件下反应,得到 4,5-二氢-3H-吡唑鎓盐 4。这些环加成反应具有完全马尔可夫尼科夫区域选择性并保留了烯烃的构型。盐3与降冰片烯的反应产生环加合物,而降冰片烷部分没有重排。根据这些观察,杂联烯 3 与烯烃的反应在机械上是一致的“反向电子需求 1,3-偶极环加成”。在溶液中,5 位有氢原子的 4,5-二氢-3H-吡唑鎓盐 4 互变异构为 4,5-二氢-1H-吡唑鎓盐 6。“一般 Wagner-Meerwein 重排”生成 1H-异构体 5y观察到化合物4y。 AM1 计算支持该机制建议。对于盐 4r 和双重环加合物 4z 进行了 X 射线结构分析。