Efficient synthesis of 1,1′-binaphthyl and 2,2′-bi-o-tolyl-2,2′-bis(oxazoline)s and preliminary use for the catalytic asymmetric allylic oxidation of cyclohexene
Efficient synthesis of 1,1′-binaphthyl and 2,2′-bi-o-tolyl-2,2′-bis(oxazoline)s and preliminary use for the catalytic asymmetric allylic oxidation of cyclohexene
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DOI：
10.1021/jo9713619
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发表时间：
1997-12-26
影响因子：
3.6
通讯作者：
Sclafani, JA
中科院分区：
文献类型：
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作者：
Andrus, MB;Asgari, D;Sclafani, JA
手性C2-对称双(恶唑啉)已成功地在许多催化不对称过程中用作各种金属的配体。这些包括环丙烷化、2 个氮丙啶化、3 个烯丙基取代、4 个氢化硅烷化、5 个亚胺加成、6 个 Diels-Alder、7 个羟醛、8 个和 Wacker 型环化 9 反应。此外，我们和 Pfaltz 最近使用双（恶唑啉）铜配合物作为催化剂，使用过苯甲酸叔丁酯进行简单烯烃的不对称烯丙基氧化。 10 虽然过去恶唑啉之间的连接基由衍生自丙二酰基前体的亚甲基单元或吡啶基单元组成，但 Corey 最近报道了一种独特的联芳基连接配体 1, 1'-双-邻甲苯基-2, 2'-双（恶唑啉）的合成，用于高选择性分子内铜催化环丙烷化反应，从而产生(-)-海妖素。 11 这种新型催化剂被证明优于多种已知的金属配体组合，包括标准亚甲基双（恶唑啉）。这种新配体的合成需要对外消旋二甲苯二甲酸前体进行制备型手性 HPLC 分离。这一步骤的高昂成本以及我们将这种新型配体应用于烯丙基氧化反应的愿望促使我们努力开发一种有效的联芳基双（恶唑啉）合成路线，该路线不依赖于手性分离或繁琐的拆分。 12 为此，采用新的不对称形式的乌尔曼偶联反应 13 来生产两种联芳基双（恶唑啉），联邻甲苯基二苯基 1 和联萘基二叔丁基 2（图 1）。我们的路线始于有效使用添加了磷酸钠的亚氯酸钠和 2-甲基丁烯14 与 1-溴-2-萘醛 311，以 94% 的产率生产酸 4（方案 1）。先前报道的使用过渡金属氧化物的氧化对于该步骤来说均较低。 12, 15 接下来的三个操作是在没有纯化或分离中间体的情况下进行的。用草酰氯和催化DMF处理4产生酰基氯，然后将其用(S)-叔亮氨醇和三乙胺处理得到酰胺。然后根据Corey的条件用Burgess试剂{[(甲氧基羰基)氨磺酰基]三乙基氢氧化铵}处理粗物质，得到恶唑啉5，总产率为89％。 9b、11 在这种情况下，发现使用二甲磺酸酯或二氯化物中间体的替代程序产率较低。 8, 13a 然后按照 Meyers 的方法与活化铜偶联，得到二邻甲苯基双（恶唑啉）2，分离收率为 77%，为白色固体（mp 109 C，[R] D
Chiral C2-symmetric bis (oxazoline) s have been successfully employed as ligands with various metals in numerous catalytic asymmetric processes. These include cyclopropanation, 2 aziridination, 3 allylic substitution, 4 hydrosilylation, 5 imine additions, 6 Diels-Alder, 7 aldol, 8 and Wacker-type cyclization9 reactions. In addition we and Pfaltz have recently used bis (oxazoline) copper complexes as catalysts for the asymmetric allylic oxidation of simple olefins using tert-butyl perbenzoate. 10 While the linker between the oxazolines in the past have consisted of a methylene unit, derived from a malonyl precursor, or a pyridyl unit, recently Corey reported the synthesis of a unique biaryl-linked ligand, 1, 1′-bis-o-tolyl-2, 2′-bis (oxazoline), for use in a highly selective intramolecular copper-catalyzed cyclopropanation reaction leading to (-)-sirenin. 11 This new catalyst was shown to superior to a variety of known metal ‚ligand combinations including the standard methylene bis (oxazoline) s. The synthesis of this new ligand required the use of a preparative chiral HPLC separation on the racemic bitolyl dicarboxylic acid precursor. The prohibitive cost of this step and our desire to apply this new class of ligands to the allylic oxidation reaction prompted the effort to develop an efficient synthetic route to biarylbis-(oxazoline) s that would not depend on a chiral separation or a tedious resolution. 12 To this end, new asymmetric versions of the Ullman coupling reaction13 were applied to produce two biarylbis (oxazoline) s, bi-o-tolyl diphenyl 1 and binaphthyl di-tert-butyl 2 (Figure 1). Our route began with the efficient use of sodium chlorite with added sodium phosphate and 2-methylbutene14 with 1-bromo-2-naphthaldehyde 311 to produce the acid 4 in 94% yield (Scheme 1). Previous oxidations reported using transition metal oxides are uniformly low for this step. 12, 15 The next three operations were performed without purification or isolation of the intermediates. Treatment of 4 with oxalyl chloride and catalytic DMF produced the acid chloride that was then treated with (S)-tert-leucinol and triethylamine to give the amide. The crude material was then treated with the Burgess reagent {[(methoxycarbonyl) sulfamoyl] triethylammonium hydroxide} according to the conditions of Corey giving oxazoline 5 in 89% overall yield. 9b, 11 Alternative procedures using the dimesylate or the dichloride intermediate were found to be lower yielding in this case. 8, 13a Coupling with activated copper following the procedure of Meyers was then performed to access bi-o-tolyl-bis (oxazoline) 2 in 77% isolated yield as a white solid (mp 109 C,[R] D