An improved procedure for the preparation of 2,2-bis[2-[4(S)-tert-butyl-1,3-oxazolinyl]]propane [(S,S)-tert-butylbis(oxazoline)] and derived copper(II) complexes
An improved procedure for the preparation of 2,2-bis[2-[4(S)-tert-butyl-1,3-oxazolinyl]]propane [(S,S)-tert-butylbis(oxazoline)] and derived copper(II) complexes
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DOI：
10.1021/jo980296f
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发表时间：
1998-06-26
影响因子：
3.6
通讯作者：
Woerpel, KA
中科院分区：
文献类型：
--
作者：
Evans, DA;Peterson, GS;Woerpel, KA
C2-对称的双（恶唑啉）（box）配体在铜催化的不对称转化中的一般效用已在许多过程中得到证实，包括环丙烷化、1烯烃氮丙啶化、2 Diels-Alder、3 Mukaiyama aldol、4和烯丙基氧化反应。5已报道了合成这些配体的几种方法，产率中等至良好。6先前报道的（S，S）-叔丁基双（恶唑啉）（（S，S）-t-Bu-box）（1）的合成，1是许多这些反应的最佳配体，在四个步骤中进行，总产率为36%。本文的目的是描述一种改进的合成1，需要最少的纯化和进行三个步骤和72%的总收率从（S）-叔亮氨酸。配体合成。我们先前制备（S，S）-t-Bu-box（1）的方法涉及氢化铝锂将市售（S）-叔亮氨酸（2）还原为相应的氨基醇3，然后用0.5当量的二甲基丙二酰二氯（6）酰化。1二羟基丙二酰胺7经双（烷基氯）（PPh_3，Et_3N，CCl_4）环化得到双恶唑啉
The general utility of C2-symmetric bis (oxazoline)(box) ligands in copper-catalyzed asymmetric transformations has been demonstrated in a number of processes, including cyclopropanation, 1 olefin aziridination, 2 Diels-Alder, 3 Mukaiyama aldol, 4 and allylic oxidation reactions. 5 Several methods for the synthesis of these ligands have been reported with moderate to good yields. 6 The previously reported synthesis of (S, S)-tert-butylbis (oxazoline)((S, S)-t-Bu-box)(1), 1 the optimal ligand for a number of these reactions, proceeded in four steps and 36% overall yield. The purpose of this paper is to describe an improved synthesis of 1 that entails minimal purification and proceeds in three steps and 72% overall yield from (S)-tert-leucine.Ligand Synthesis. Our previous method for preparing (S, S)-t-Bu-box (1) involved lithium aluminum hydride reduction of commercially available (S)-tert-leucine (2) to the corresponding amino alcohol 3, followed by acylation with 0.5 equiv of dimethylmalonyl dichloride (6). 1 The dihydroxy malonodiamide 7 was cyclized to the bis-(oxazoline) via the bis (alkyl chloride)(PPh3, Et3N, CCl4)