Department of Chemistry, Dalhousie University, Nova Scotia, B3H 4R2, Canada.
Chemistry. 2011 Jul 11;17(29):8098-104. doi: 10.1002/chem.201100519. Epub 2011 Jun 7.
Alkyl substitution α to the ketone of an allenyl vinyl ketone enhances Nazarov reactivity by inhibiting alternative pathways involving the allene moiety and through electron donation and/or steric hindrance. This substitution pattern 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 of the Nazarov process for allenyl vinyl ketones was determined to be a result of an electronic bias in the oxyallyl cation intermediate. Computational data are consistent with this observation.
α 位取代烯丙基乙烯基酮的酮可以通过抑制涉及丙二烯部分的替代途径以及通过电子给予和/或空间位阻来增强纳扎罗夫反应性。这种取代模式还通过增加反应性构象体的数量和稳定氧杂丙烯阳离子中间体来加速纳扎罗夫环化。此外，当氧杂丙烯阳离子中间体被亲核氧添加或与非环状二烯进行 [4+3] 环化时，用烷基取代α 位不会改变中断的纳扎罗夫反应的区域选择性。烯丙基乙烯基酮的纳扎罗夫反应的区域选择性被确定为氧杂丙烯阳离子中间体中的电子偏置的结果。计算数据与这一观察结果一致。
