Enantiomerically pure allylboronic esters 1 + 2 with a stereogenic center α to the boron moiety can be obtained by a sigmatropic rearrangement of boron containing allyl alcohols. Allyl additions with the new reagents are highly selective, which was shown via the direct measurement of the diastereoisomeric ratio of the intermediates 5 + 6 by characteristic NMR chemical shifts. The observations are not limited to ester containing reagents, but holds also true for hydrocarbon side-chains (e.g. in 11 + 12) that were readily obtained by reducing the ester.
通过对含
硼烯丙基醇进行对称重排,可以得到对映体纯的烯丙基
硼酸酯 1 + 2,其
硼分子的立体中心为δ。新试剂的烯丙基加成具有很高的选择性,这可以通过特征核磁共振
化学位移直接测量中间产物 5 + 6 的非对映异构体比率来证明。这些观察结果并不局限于含酯试剂,通过还原酯很容易得到的碳氢化合物侧链(如 11 + 12 中的碳氢化合物侧链)也是如此。