Design of N-spiro C2-symmetric chiral quaternary ammonium bromides as novel chiral phase-transfer catalysts:: Synthesis and application to practical asymmetric synthesis of α-amino acids
Design of N-spiro C2-symmetric chiral quaternary ammonium bromides as novel chiral phase-transfer catalysts:: Synthesis and application to practical asymmetric synthesis of α-amino acids
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DOI：
10.1021/ja021244h
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发表时间：
2003-04-30
影响因子：
15
通讯作者：
Maruoka, K
中科院分区：
文献类型：
--
作者：
Ooi, T;Kameda, M;Maruoka, K
设计了一系列C-2对称的手性溴化季铵10和1,1作为一种新的、纯合成的手性相转移催化剂，并且容易地由市售的光学纯1，1 ′-联-2-萘酚作为基本手性单元制备。详细介绍了每种手性联萘亚基的合成方法，并通过单晶X-射线衍射分析确定了所合成的N-螺环手性溴化季铵11 a和11 f的结构。在温和的液-液相转移条件下，考察了这些手性溴化铵作为手性相转移催化剂在二苯甲酮Schiff碱甘氨酸酯7不对称烷基化反应中的反应活性和选择性，并对反应条件（溶剂、碱和温度）进行了优化.此外，这种不对称烷基化的范围和限制已经用各种烷基卤化物进行了彻底的研究，其中特别强调了11的独特N-螺环结构的优点以及一个联萘部分的3，3 '-位上的芳族取代基的空间和电子性质的显著影响。最后，本发明的方法用于结构多样的天然和非天然α-氨基酸的实际不对称合成的潜在合成效用已经通过其成功应用于（S）-N-乙酰基吲哚啉-2-羧酸酯（ACE抑制剂合成中的关键中间体）和L-多巴（L-3，4-二羟基苯丙氨酸）酯及其类似物的简易不对称合成而得到证实。
A series of C-2-symmetric chiral quaternary ammonium bromides 10 and 11 have been designed as a new, purely synthetic chiral phase-transfer catalyst, and readily prepared from commercially available optically pure 1,1'-bi-2-naphthol as a basic chiral unit. The details of the synthetic procedures of each requisite chiral binaphthyl subunit have been disclosed, and the structures of the assembled N-spiro, chiral quaternary ammonium bromides 11a and 11f were unequivocally determined by single-crystal X-ray diffraction analysis. The reactivity and selectivity of these chiral ammonium bromides as chiral phase-transfer catalysts have been evaluated in the asymmetric alkylation of the benzophenone Schiff base of glycine ester 7 under mild liquid-liquid phase-transfer conditions, and the optimization of the reaction variables (solvent, base, and temperature) has also been conducted. Further, the scope and limitations of this asymmetric alkylation have been thoroughly investigated with a variety of alkyl halides, in which the advantage of the unique N-spiro structure of 11 and dramatic effect of the steric as well as the electronic properties of the aromatic substituents on the 3,3'-position of one binaphthyl moiety have been particularly emphasized. Finally, the potential synthetic utility of the present method for the practical asymmetric synthesis of structurally diverse natural and unnatural alpha-amino acids has been demonstrated by its successful application to the facile asymmetric syntheses of (S)-N-acetylindoline-2-carboxylate, a key intermediate in the synthesis of the ACE inhibitor, and L-Dopa (L-3,4-dihydroxyphenylaianine) ester and its analogue.