Department of Chemistry, Rikkyo University, Toshima-ku, Tokyo, Japan.
J Org Chem. 2011 Jun 3;76(11):4652-60. doi: 10.1021/jo200728t. Epub 2011 May 12.
The reactions of oximes to amides, known as the Beckmann rearrangement, may undergo fragmentation to form carbocations + nitriles when the migrating groups have reasonable stability as cations. The reactions of oxime sulfonates of 1-substituted-phenyl-2-propanone derivatives (7-X) and related substrates (8-X, 9a-X) in aqueous CH(3)CN gave both rearrangement products (amides) and fragmentation products (alcohols), the ratio of which depends on the system; the reactions of 7-X gave amides predominantly, whereas 9a-X yielded alcohols as the major product. The logk-logk plots between the systems gave excellent linear correlations with slopes of near unity. The results support the occurrence of path bifurcation after the rate-determining TS of the Beckmann rearrangement/fragmentation reaction, which has previously been proposed on the basis of molecular dynamics simulations. It was concluded that path-bifurcation phenomenon could be more common than thought and that a reactivity-selectivity argument based on the traditional TS theory may not always be applicable even to a well-known textbook organic reaction.
肟对酰胺的反应，即贝克曼重排，当迁移基团作为阳离子具有合理的稳定性时，可能会发生碎裂，形成碳正离子和腈。1-取代苯基-2-丙酮衍生物（7-X）及其相关底物（8-X、9a-X）的肟磺酸盐在含水 CH(3)CN 中的反应既生成重排产物（酰胺），也生成碎裂产物（醇），其比例取决于体系；7-X 的反应主要生成酰胺，而 9a-X 则以醇为主要产物。系统之间的 logk-logk 图给出了极好的线性相关，斜率接近 1。结果支持了在 Beckmann 重排/碎裂反应的速率决定过渡态之后发生路径分叉的假设，这一假设以前是基于分子动力学模拟提出的。可以得出结论，分叉现象可能比想象的更为普遍，即使对于一个众所周知的经典有机反应，基于传统过渡态理论的反应选择性论点也不一定总是适用。
