Endo Entry to the Nortricyclyl−Norbornenyl Cation System: Stereochemistry in the Fragmentation of <i>endo</i>-5-Norbornenyl-2-oxychlorocarbene
作者:Robert A. Moss、Xiaolin Fu、Ronald R. Sauers、Peter Wipf
DOI:10.1021/jo051222o
日期:2005.10.1
mainly to retention and inversion SNi transition states, respectively. These have been located by computational methods and are nearly isoenergetic. In more polar solvents (CDCl3 and CD3CN), the fragmentation of (S)-8 increasingly occurs via competitive ion pair pathways in which steroselectivity is diminished, and escape to the norbornenyl−nortricyclyl cation directs the products away from endo-2-chloro-5-norbornene
(碎裂小号) -内型-5-降冰片烯-2- oxychlorocarbene [(小号) - 8 ]在环己烷d 12给出〜20%(小号) -内型-2-氯-5-降冰片烯[(小号) - 7 ee约50%,ee≥95%的65-70%(R)-exo -2-氯-5-降冰片烯[(R)-4 ]和ee约12%的(R)-3-nortricyclyl chloride [[ R ] -4 ] (R)-5 ],ee约为22%。(从对映体卡宾(R)-8开始也获得了类似的立体化学结果。)(S)-8至(S)-7和(S)-8至(R)-4转换分别主要归因于保留和反转S N i过渡态。这些已经通过计算方法定位,并且几乎是等能量的。在极性更大的溶剂(CDCl 3和CD 3 CN)中,(S)-8的碎裂越来越多地通过竞争性离子对途径发生,其中立体选择性降低,并逃逸到降冰片烯基-北三环基阳离子中,从而使产物远离内消旋-2-氯-5-降