Heteroatom Influence on the π-Facial Selectivity of Diels−Alder Cycloadditions to 1-Oxa-4-thia-6-vinylspiro[4.5]dec-6-ene, 3-Methoxy-3-methyl-2-vinylcyclohexene, and 3-Methoxy-2-vinylcyclohexene<sup>,</sup>
作者:Veejendra K. Yadav、Govindaraji Senthil、K. Ganesh Babu、Masood Parvez、Jennifer Lee Reid
DOI:10.1021/jo0106400
日期:2002.2.1
orbital on the acetal oxygen and the orthogonal pi-orbital of the acetylene unit in DMAD in the syn-to-oxygen addition of the latter. This repulsion is offset on coordination of Li+ to the said oxygen electron pair orbital, and the addition thus proceeds syn to oxygen. The enhanced and accelerated syn-to-oxygen addition in lithium perchlorate in nitromethane is interpreted as a consequence of the coordination
研究了几种亲二烯体对标题底物的狄尔斯-阿尔德环加成反应的面部选择性。观察到的选择性被解释为取代基提供的相对空间相互作用的结果。乙炔二羧酸二甲酯(DMAD)的添加受静电排斥的影响,该静电排斥是乙醛中的电子对轨道与乙炔单元中乙炔单元的正交π轨道在正-氧加成中相互作用而产生的。该排斥在Li +与所述氧电子对轨道配位时被抵消,因此加成与氧同步进行。硝基甲烷中高氯酸锂中合成氧的增加和加速被解释为是由于Li +与亲二烯体中乙缩醛氧和杂原子的配位作用,使它们紧密靠近以促进反应。然而,Li +-氧的组合还发挥一些空间效应,导致具有大取代基的亲二烯体如N-苯基马来酰亚胺的合成氧加成减少。