Palladium-catalyzed asymmetric addition of pronucleophiles to allenes
Palladium-catalyzed asymmetric addition of pronucleophiles to allenes
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DOI：
10.1021/ja029190z
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发表时间：
2003-04-16
影响因子：
15
通讯作者：
Plietker, B
中科院分区：
文献类型：
--
作者：
Trost, BM;Jäkel, C;Plietker, B
简单的加成是实现烷基化最经济的原子方式。不对称地进行丙二烯烃化的能力就成为一种高效的烷基化方案。这种方案的第一个例子涉及衍生自三氟乙酸钯二聚体和反式-1,2-二氨基环己烷的双-2-二苯基膦基苯甲酰胺的钯(0)催化剂催化加成到苄氧基烯烃的能力。各种取代的米德鲁姆酸（包括羟基米德鲁姆酸）在 1 mol% 三氟乙酸存在下反应良好，得到一种 ee 范围为 82% 至 99% 的区域异构体。改用吖内酯来获取不寻常的季氨基酸需要更基本的条件。因此，使用 2 mol% α-丁醇钾和 20 mol% 马尿酸可以顺利反应，生成简单的区域异构体。这种亲核试剂提出了对于亲核试剂和亲电试剂的面选择性问题。获得了优异的非对映选择性 (dr 13−20:1) 和对映选择性 (85−94% ee)。因此，通过简单加成对碳亲核试剂进行不对称烯丙基烷基化的新方法为不对称CC键的形成提供了一种非常有效、更原子经济的策略。
Simple additions are the most atom economic way to effect alkylations. The ability to effect the hydrocarbonation of allenes asymmetrically then becomes a highly efficient alkylation protocol. The first example of such a protocol involves the ability of a palladium(0) catalyst derived from palladium trifluoroacetate dimer and the bis-2-diphenylphosphinobenzamide oftrans-1,2-diamininocyclohexane to catalyze additions to benzyloxyalkene. Various substituted Meldrum's acids including hydroxy Meldrum's acid react well in the presence of 1 mol % trifluoroacetic acid to give one regioisomer with ee's ranging from 82 to 99%. Switching to azlactones to access unusual quarternary amino acids requires somewhat more basic conditions. Thus, use of 2 mol % potassium α-butoxide and 20 mol % hippuric acid leads to a smooth reaction to produce a simple regiosomer. This nucleophile raises the question of facial selectivity with respect to both the nucleophile and the electrophile. Excellent diastereoselectivity (dr 13−20:1) and enantioselectivity (85−94% ee) are obtained. Thus, a new approach for asymmetric allylic alkylations of carbon pronucleophiles by simple additions provides a very efficient, more atom economic strategy for asymmetric C−C bond formation.