Asymmetric conjugate addition of alkynylboronates to enones
Asymmetric conjugate addition of alkynylboronates to enones
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DOI：
10.1021/ja992922b
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发表时间：
2000-03-01
影响因子：
15
通讯作者：
Taylor, NJ
中科院分区：
文献类型：
--
作者：
Chong, JM;Shen, LX;Taylor, NJ
将金属有机化合物，特别是有机铜和有机锌2加成到R，-不饱和羰基化合物上是一种公认的形成碳-碳键的方法。在过去的二十年里，这些反应的不对称版本，特别是铜试剂，已经被开发出来，具有很高的选择性。然而，有机铜试剂的一个重要限制是它们不能有效地将炔基转移到有机底物上（方案1）。5由于炔基可以很容易地被操纵成许多其他官能团，6我们有兴趣通过开发反应来填补这一空白，这些反应可以以迈克尔方式立体选择性地将炔基添加到R，-不饱和羰基化合物上。我们现在报告了炔基对烯酮的对映选择性共轭加成的第一个例子。用非手性试剂与炔基硼(8)和铝(9)进行了共轭炔基转移。然而，似乎没有这些反应的不对称版本的报道。我们推断手性二醇的炔基硼酸衍生物可能是一种不对称共轭炔基化试剂。10-12 1,1 ' -双-2-萘酚在许多不对称转化中被用作非常有效的手性助剂13，因此我们最初的努力是制备一般结构为2的试剂（方案2）。先前已经表明，炔基硼酸盐可能是预-
Michael addition of organometallics, particularly organocoppers1 and organozincs, 2 to R,-unsaturated carbonyl compounds is a well-established method for the formation of carbon-carbon bonds. Over the past two decades, asymmetric versions of these reactions, particularly with copper reagents, have been developed which can be highly selective. 3, 4 However, one important limitation of organocopper reagents is that they do not efficiently transfer alkynyl groups to organic substrates (Scheme 1). 5 Since alkynyl groups may be readily manipulated into many other functionalities, 6 we were interested in filling this void by developing reactions which could stereoselectively add alkynyl groups in a Michael fashion to R,-unsaturated carbonyl compounds. We now report the first examples of enantioselective conjugate additions of alkynyl groups to enones. 7 Conjugate alkynyl group transfer using achiral reagents had been achieved with alkynylboron8 and aluminum9 reagents. However, it appears that no asymmetric versions of these reactions have been reported.We reasoned that an alkynylboronate derivative of a chiral diol might be an asymmetric conjugate alkynylation reagent. 10-12 1, 1′-Bi-2-naphthol has been used as a very effective chiral auxiliary in many asymmetric transformations13 so we directed our initial efforts to prepare reagents of general structure 2 (Scheme 2). It has previously been shown14 that alkynylboronates may be pre-