Asymmetric allyl- and crotylboration with the robust, versatile, and recyclable 10-TMS-9-borabicyclo[3.3.2]decanes
Asymmetric allyl- and crotylboration with the robust, versatile, and recyclable 10-TMS-9-borabicyclo[3.3.2]decanes
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DOI：
10.1021/ja043612i
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发表时间：
2005-06-08
影响因子：
15
通讯作者：
Soderquist, JA
中科院分区：
文献类型：
--
作者：
Burgos, CH;Canales, E;Soderquist, JA
报道了10-（三甲基硅基）-9-硼比环[3.3.2]十烷（10- tms -9- bbds）在代表性醛的烯丙基和丁基化反应中的显著通用性和选择性。新试剂是由10- tivis -9- bbd(4)的空气稳定晶体伪麻黄碱硼酸酯配合物制备的，通过简单的两步程序，B-MeO-9-BBN的总收率为63%。这些配合物4与烯丙基溴化镁直接转化为相应的b -烯丙基-10- tms -9- bbds(1)，可以分离（98%）或原位用于烯丙基化反应。这些试剂在-78℃下快速（< 3 h）、不对称烯基硼化反应中具有显著的对映选择性（96 ~ >= 99% ee），在25℃下进行时仅略有降低，这是由于其刚性双环结构。除了有效地提供同丙烯醇6（68-80%）外，该程序还允许有效地回收4（68-84%）以直接再生1。或者，氧化后处理程序可用于制备6。该试剂具有可预测的立体化学性质，并在d -甘油醛丙酮烯丙基硼化反应中表现出极高的试剂控制水平。已经开发了一种简单有效的方法，可以从光学纯的B-MeO-10-TMS-9-BBD(3)的对映体中制备b -crotyl-10- tms -9- bbd（10）的所有四种几何和对映体异构体（10）。这些试剂10还能在-78℃下快速（< 3 h）有效地添加到代表性的醛，提供了高dr（>= 98:2）和ee（94-99%）的对甲基同丙烯醇12-15（69-92%）的所有四种可能的立体异构体。
The remarkable versatility and selectivity of the 10-(trimethylsilyl)-9-borabicyclo[3.3.2]decanes (10-TMS-9-BBDs) in the allyl- and crotylboration of representative aldehydes are reported. The new reagents are prepared through air-stable crystalline pseudoephedrine borinic ester complexes of the 10-TIVIS-9-BBDs (4), which are available in 63% overall yield from B-MeO-9-BBN through a simple two-step procedure. These complexes 4 are directly converted to the corresponding B-allyl-10-TMS-9-BBDs (1) with allylmagnesium bromide, which either can be isolated (98%) or used in situ for the allylations. The remarkable enantioselectivity (96 to >= 99% ee) of these reagents in the rapid (< 3 h), asymmetric allylboration process at -78 degrees C is only slightly diminished when it is conducted at 25 degrees C, a phenomenon attributable to its rigid bicyclic structure. In addition to providing the homoallylic alcohols 6 efficiently (68-80%), the procedure also permits the efficient recovery of 4 (68-84%) for the direct regeneration of 1. Alternatively, an oxidative workup procedure can be used for the preparation of 6. The reagent gives predictable stereochemistry and exhibits an extremely high level of reagent control in the allylboration Of D-glyceraldehyde acetonide. A simple and efficient procedure has been developed for the preparation of all four geometric and enantiomeric isomers of the B-crotyl-10-TMS-9-BBDs (10) from optically pure enantiomers of B-MeO-10-TMS-9-BBD (3). These reagents 10 also add rapidly (< 3 h) and efficiently to representative aldehydes at -78 degrees C, providing ready access to all four of the possible stereoisomers of the P-methyl homoallylic alcohols 12-15 (69-92%) in high dr (>= 98:2) and ee (94-99%).