Enantiomerically pure cyclopropylboronic esters: auxiliary- versus substrate-control
作者:Jörg Pietruszka、Andreas Witt
DOI:10.1039/b006970l
日期:——
Stable, enantiomerically pure cyclopropylboronic esters are synthesized from alkynes by a hydroboration–cyclopropanation sequence. The direct hydroboration—utilizing 1,3,2-dioxaborolane 4—is most convenient, however, with more functionalized side-chains it failed to give the desired intermediates. Using the more reactive dicyclohexylborane, followed by oxidation and transesterification, is a good alternative
稳定的对映体纯的环丙基硼酸酯是由炔烃通过硼氢化-环丙烷化顺序合成的。使用1,3,2-二氧杂硼环烷4进行直接硼氢化反应是最方便的方法,但是,由于侧链功能化,未能提供所需的中间体。使用反应性更高的二环己基硼烷,然后进行氧化和酯交换反应,是一种不错的一锅转化方法。按照Simmons-Smith方案或使用重氮甲烷-钯(II)乙酸酯进行环丙烷化。将对辅助剂1的非对映选择性的影响与侧链中另外的立体异构中心的影响进行比较。