Intramolecular nucleophilic addition of phenolate to unactivated double and triple bonds. Relative reactivity, regiospecificity, stereochemistry, and mechanism
作者:Christopher M. Evans、Anthony J. Kirby
DOI:10.1039/p29840001269
日期:——
much greater reactivity of alkynes, compared with the alkenes, towards nucleophilic attack is primarily a transition-state property, reflecting the greater stability of the sp2(compared with sp3)-hybridised carbanions produced. Antiperiplanar addition is probably involved in all these reactions. There is little difference in intrinsic reactivity between 5-exo, 6-exo, and 6-endo-trig olefin cyclisations
苯酚氧分子内的亲核分子加成到一系列末端乙炔的未活化三键(11)是一个两步过程,涉及速率确定乙烯基碳负离子的形成。反应比相应烯烃的环化快10 4倍(机理改变已经减少了这一因素)。相应的甲基乙炔(18)的环化超过10 3慢速,通常是酸催化的,大概是因为甲基取代的乙烯基碳负离子是一种高能的物质。显然,与烯烃相比,炔烃对亲核进攻的反应性更高,这主要是一种过渡态性质,反映了产生的sp 2(与sp 3)杂化碳负离子的稳定性更高。所有这些反应都可能涉及到腹膜外添加。5- exo,6- exo和6 -endo-trig烯烃环化之间的内在反应性差异不大,但是5- exo优先于6 -endo-dig的环内反应 乙炔反应的模式。