Substituent-Controlled Reactivity in the Nazarov Cyclisation of Allenyl Vinyl Ketones
作者:Vanessa M. Marx、Rhonda L. Stoddard、Gavin S. Heverly-Coulson、D. Jean Burnell
DOI:10.1002/chem.201100519
日期:2011.7.11
also accelerates Nazarov cyclisation by increasing the population of the reactive conformer and by stabilising the oxyallyl cation intermediate. Furthermore, α substitution by an alkyl group does not alter the regioselectivity of interrupted Nazarov reactions when the oxyallyl cation intermediate is intercepted by addition of an oxygen nucleophile, or by [4+3] cyclisation with acyclic dienes. The regioselectivity
烯丙基乙烯基酮的酮上的烷基取代α通过抑制涉及丙二烯部分的替代途径以及通过电子给体和/或位阻,增强了Nazarov反应性。该取代模式还通过增加反应性构象异构体的数量并稳定了氧基烯丙基阳离子中间体而加速了纳扎罗夫环化反应。此外,当通过添加氧亲核试剂或通过与无环二烯进行的[4 + 3]环化来拦截羟烯丙基阳离子中间体时,烷基取代α不会改变中断的Nazarov反应的区域选择性。Nazarov工艺对烯丙基乙烯基酮的区域选择性被确定为是由于羟基烯丙基阳离子中间体中的电子偏向的结果。计算数据与该观察结果一致。