Stereoselectivity of alkylidenecarbene addition to olefins. 2. Effect of orbital polarization in the alkenes
作者:Dennis P. Fox、Peter J. Stang、. Apeloig. Yitzhak、Miriam. Karni
DOI:10.1021/ja00264a029
日期:1986.2
R and x* orbitals are strongly polarized in the same direction, as in styrene. The results also are discussed relative to earlier MNDO calculations. Recently we reported a detailed experimental and theoretical investigation of the stereoselectivity of alkylidenecarbene additions to o1efins.l Unsymmetrical alkylidenecarbenes R(CH,)C=C: (1-3) were found experimentally to add to two unsymmetrical olefins
研究了不对称亚烷基卡宾 R(CH3)C=C: 与三种不对称烯烃、1-丁烯、苯乙烯和乙基乙烯基醚的反应,其中 R = i-Pr (2) 和 t-Bu (3)。在每种情况下,E 烯烃加合物都比 Z 加合物占优势。发现立体选择性按以下顺序降低(EZ 产物比率与 3 在 -20"C) 苯乙烯 (250:l) >> 乙基乙烯基醚 (1 1.5:l) > 叔丁基乙烯 (1O:l) > 1-丁烯(4.3:l) > 异丁烯 (2.0:l); 对所有烯烃的立体选择性要低得多。正如之前预测的那样,具有更高极化 R 轨道的烯烃,苯乙烯和乙基乙烯基醚,产生了最大的立体选择性反应。还确定烯属 R* 轨道的数量会影响环加成的立体选择性。只有 R 和 x* 轨道在相同方向上强烈极化的烯烃才具有高立体选择性,如在苯乙烯中。还讨论了与早期 MNDO 计算相关的结果。最近我们报道了对亚烷基卡宾加成到烯烃的立体选择性的详细实验和理论研究。l