CHIRAL SYNTHESIS VIA ORGANOBORANES .5. ASYMMETRIC ALLYLBORATION VIA CHIRAL ALLYLDIALKYLBORANES - SYNTHESIS OF HOMOALLYLIC ALCOHOLS WITH EXCEPTIONALLY HIGH ENANTIOMERIC EXCESS
CHIRAL SYNTHESIS VIA ORGANOBORANES .5. ASYMMETRIC ALLYLBORATION VIA CHIRAL ALLYLDIALKYLBORANES - SYNTHESIS OF HOMOALLYLIC ALCOHOLS WITH EXCEPTIONALLY HIGH ENANTIOMERIC EXCESS
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DOI：
10.1021/jo00354a003
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发表时间：
1986-02-21
影响因子：
3.6
通讯作者：
BROWN, HC
中科院分区：
文献类型：
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作者：
JADHAV, PK;BHAT, KS;BROWN, HC
烯丙基二异蒎蒎基硼烷可通过用烯丙基溴化镁处理甲氧基二异蒎蒎基硼烷轻松地制备，可顺利地与醛加成，具有显着的对映选择性，将烯丙基转移到羰基碳上，同时硼转移到氧上。烯丙基硼化反应中的对映选择性随反应温度的变化而变化，当温度从 0°C 降至零下 78°C 时，对映选择性会显着增加。然而，所达到的对映选择性并不随醛的结构而显着变化。试剂与代表性酮缩合时的对映选择性不太有利，但在某些情况下，结果很有希望（高达 75% ee）。甲代烯丙基二异松蒎基硼烷和(3, 3-二甲基-烯丙基)二异蒎蒎基硼烷与醛的缩合以同样高的不对称诱导进行，表明可以适应烯丙基部分结构的广泛变化。还研究了手性配体的变化对硼的影响。烯丙基硼烷是极其活泼的有机硼烷中间体。 1 烯丙基硼烷的高反应性表现在它们与水、醇和胺的反应，甚至在室温下也会发生。 13 这一特征使它们与三烷基硼烷显着区别，后者仅在高温下与相同底物发生反应。在过去的十年中，米哈伊洛夫和他的同事13广泛研究了简单的三烯基硼烷的化学性质。他们报道称，这种烯基硼烷以通常的有机金属方式顺利地加成到各种羰基衍生物上，将烯丙基转移到羰基碳上，同时硼转移到氧上（式1）。醛和酮的此类烯丙基硼化反应
Allyldiisopinocampheylborane, prepared readily by treatment of methoxydiisopinocampheylborane with al-lylmagnesium bromide, adds smoothly to aldehydes with remarkable enantioselectivity, transferring an allyl group to the carbonyl carbon with boron going to the oxygen. The enantioselectivity in allylboration varies with the reaction temperature, increasing considerably by decreasing the temperature from 0 C to-78 C. However, the enantioselectivity achieved does not vary significantly with the structureof the aldehyde. The enantioselectivity in the condensation of the reagent with representative ketones is less favorable, but in selected cases the results are promising (as high as 75% ee). Condensation of methallyldiisopinocampheylborane and (3, 3-dimethyl-allyl) diisopinocampheylborane with aldehydes proceeds with equally high asymmetric induction, indicating that wide variations in the structure of the allylic moiety can be accommodated. The effect of changes in the chiral ligand on boron has also been studied.Allylboranes are extremely reactive organoborane in-termediates. 1 The high reactivity of allylboranes is manifested in their reactions with water, alcohols, and amines, which occur even at room temperature. 13 This feature distinguishes them markedly from trialkylboranes, which react with the same substrates only at elevated temperatures. Over the pastdecade, Mikhailov and co-workers13 haveextensively examined the chemistry of the simple triallylboranes. They have reported that such al-lylboranes add smoothly to various carbonyl derivatives in the usual organometallic fashion, transferring an allyl group to the carbonyl carbon with boron going to the ox-ygen (eq 1). Such allylborations of aldehydes and ketones