Herbert C. Brown Laboratories of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47907-2084, USA.
Org Lett. 2009 Sep 17;11(18):4092-5. doi: 10.1021/ol901566e.
Contrary to all previous reports, bromoboration of propyne with BBr(3) proceeds in >or=98% syn-selectivity to produce (Z)-2-bromo-1-propenyldibromoborane (1). Although 1 is readily prone to stereoisomerization, it can be converted to the pinacolboronate (2) of >or=98% isomeric purity by treatment with pinacol, which may then be subjected to Negishi coupling to give trisubstituted (Z)-alkenylpinacolboronates (3) containing various R groups in 73-90% yields. Iodinolysis of 3 affords alkenyl iodides (4) in 80-90% yields. All alkenes isolated and identified are >or=98% Z.
与之前所有的报道相反，丙炔与 BBr(3) 的溴化反应以大于或等于 98%的 syn-选择性进行，生成(Z)-2-溴-1-丙烯基二溴化硼(1)。尽管 1 容易发生立体异构化，但通过与频哪醇反应可以将其转化为大于或等于 98%的异构纯 pinacolboronate(2)，然后可以通过 Negishi 偶联反应得到含有各种 R 基团的三取代(Z)-烯基频哪醇硼烷(3)，产率为 73-90%。3 的碘解反应以 80-90%的产率得到烯基碘化物(4)。分离和鉴定的所有烯烃的 Z 构型大于或等于 98%。
