Asymmetric hetero-Diels-Alder reactions of N-sulfinyl dienophiles using chiral bis(oxazoline)-copper(II) and -zinc(II) triflates
Asymmetric hetero-Diels-Alder reactions of N-sulfinyl dienophiles using chiral bis(oxazoline)-copper(II) and -zinc(II) triflates
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DOI：
10.1021/jo0490245
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发表时间：
2004-10-15
影响因子：
3.6
通讯作者：
Gautun, OR
中科院分区：
文献类型：
--
作者：
Bayer, A;Endeshaw, MM;Gautun, OR
描述了N-亚磺酰基亲双烯体与双（恶唑啉）三氟甲磺酸铜（II）和双（恶唑啉）三氟甲磺酸锌（II）的不对称Hetero-Diels -桤木（HDA）反应。研究了环状和非环状1，3-二烯的环加成反应。在大多数情况下，用化学计量量的刘易斯酸获得了良好的对映选择性（70- 98%ee）和产率（60-85%）。环状二烯的主要产物为内加成物，而非环状二烯的主要产物为顺式加成物。HDA加合物已转化为N-保护的α-氨基酸甲酯、氨基醇和高烯丙基胺。一个立体化学模型，它占的对映体选择性的HDA反应的四面体金属中心，已被提出。机制研究显示，积极的非线性效应，假定从形成反应性较低的异手性复合物。温度依赖性的对映体选择性的调查表明，至少有两个选择性的反应步骤存在于锌催化反应。用10摩尔%手性刘易斯酸进行的反应得到差的产率和选择性。然而，与TMSOTf（100摩尔%）组合，获得高产率（68-86%）和对映体选择性（97- 98%ee）。
Asymmetric hetero-Diels -Alder (HDA) reactions of N-sulfinyl dienophiles using bis(oxazoline)copper(II) and -zinc(II) triflates are described. The cycloadditions with cyclic and acyclic 1,3-dienes have been studied. In most cases, good enantioselectivities (70-98% ee) and yields (60-85%) were obtained with stoichiometric amounts of the Lewis acids. Cyclic dienes gave the endo adducts as major products, while acyclic dienes provided cis adducts. The HDA adducts have been transformed into N-protected alpha-amino acid methyl esters, amino alcohols, and homoallylic amines. A stereochemical model, which accounts for the enantiofacial selectivity of the HDA reaction by a tetrahedral metal center, has been proposed. Mechanistic studies revealed positive nonlinear effects, assumed to arise from the formation of less-reactive heterochiral complexes. Investigation of the temperature dependence of the enantio selectivity indicated that at least two selective reaction steps exist in the zinc-catalyzed reaction. Reactions run with 10 mol % chiral Lewis acid gave poor yields and selectivities. However, in combination with TMSOTf (100 mol %), high yields (68-86%) and enantioselectivities (97-98% ee) were obtained.