The use of chiral diferrocenyl diselenides for highly selective asymmetric intramolecular selenocyclisation
作者:Hiroya Takada、Yoshiaki Nishibayashi、Sakae Uemura
DOI:10.1039/a901087d
日期:——
Asymmetric intramolecular selenocyclisation of alkenoic acids, alkenols and alkenyl urethanes using chiral 2-[1-(dimethylamino)ethyl]ferrocenylselenenyl cations proceeds smoothly to give the corresponding organoselenenyl moiety-containing lactones, cyclic ethers and N-heterocycles, respectively, in good to excellent chemical yields (up to 97%) with very high diastereoselectivities (up to 98% de). The nature of the counter anions of the selenenylating agents affected remarkably the diastereoselectivity of the cyclisation, PF6– and BF4– being revealed to be the best for alkenoic acids and alkenols, and alkenyl urethanes, respectively. A plausible reaction scheme for the cyclisation is presented where a chiral selenenylating agent approaches the carbon–carbon double bond of the substrate from the less sterically-congested direction to afford a chiral episelenonium ion followed by an intramolecular back side attack of a nucleophile.
不对称的分子内硒环化反应针对烯酸、烯醇和烯基氨基甲酸酯,采用手性2-[1-(二甲基氨基)乙基]铁烯基硒正离子顺利进行,生成相应的含有有机硒基团的内酯、环醚和氮杂环,化学收率良好到优异(高达97%),且具有非常高的diastereoselectivity(高达98%去对映体选择性)。硒化试剂的反离子性质显著影响了环化反应的diastereoselectivity,PF6–和BF4–分别被证明是烯酸和烯醇、烯基氨基甲酸酯的最佳选择。提出了一个合理的反应机制,其中手性硒化试剂从立体空间上不拥挤的方向靠近底物的碳-碳双键,形成手性的episelenonium离子,随后发生亲核试剂的分子内背面攻击。