Asymmetric synthesis of β-amino acids by addition of chiral enolates to nitrones via N-acyloxyimininm ions
Asymmetric synthesis of β-amino acids by addition of chiral enolates to nitrones via N-acyloxyimininm ions
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DOI：
10.1246/bcsj.73.2423
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发表时间：
2000-11-01
影响因子：
4
通讯作者：
Murahashi, S
中科院分区：
文献类型：
--
作者：
Kawakami, T;Ohtake, H;Murahashi, S
N-酰氧亚胺离子是由硝酮与酰基卤化物反应生成的，是一种活性很高的物种，它可以与多种亲核试剂如烯酮硅缩醛、钛(IV)和硼烯醇酸盐、氢化和烯丙基锡(IV)试剂以及炔基钛(IV)试剂反应，生成α-取代胺衍生物。通过N-酰氧亚胺离子与含手性助剂的硼和钛(IV)烯醇酸盐反应，可以得到光学活性的β-氨基酸。通过硼和钛(IV)烯醇酸盐的反应，观察到非对映选择性的逆转。使用这些反应，例如，α-甲基-β-苯丙氨酸的所有四个立体异构体都可以高度非对映选择性地制备。环状N-酰氧亚胺离子可用于吡咯烷和哌啶生物碱的不对称合成，选择性地合成了合成5-取代8-甲基吲哚咪啶的关键中间体--(5R，8R，8AS)-5-氰基-8-甲基吲哚肼。
N-Acyloxyiminium ions, generated by the reaction of nitrones with acyl halides, are highly reactive species and undergo facile reaction with a wide range of nucleophiles, such as ketene silyl acetals, titanium(IV) and boron enolates, hydrido- and allyltin(IV) reagents, and alkynyltitanium(IV) reagents, to give alpha -substituted amine derivatives. Optically active beta -amino acids can be prepared by the reaction of N-acyloxyiminium ions with both boron and titanium(IV) enolates bearing chiral auxiliaries. Reversal of diastereoselectivity was observed by the reactions of the boron and titanium(IV) enolates. Using these reactions, all of the four stereoisomers of alpha -methyl-beta -phenylalanines, for example, can be prepared highly diastereoselectively. Cyclic N-acyloxyiminium ions are useful for the asymmetric synthesis of pyrrolidine and piperidine alkaloids; (5R,8R,8aS)-5-cyano-8-methylindolizidine which is a common key intermediate for synthesis of 5-substituted 8-methylindolizidines, was prepared selectively.