Construction of enantiomerically enriched tertiary α-hydroxycarboxylic acid derivatives by phase-transfer-catalyzed asymmetric alkylation of diaryloxazolidin-2,4-diones
Construction of enantiomerically enriched tertiary α-hydroxycarboxylic acid derivatives by phase-transfer-catalyzed asymmetric alkylation of diaryloxazolidin-2,4-diones
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DOI：
10.1002/anie.200600470
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发表时间：
2006-01-01
影响因子：
16.6
通讯作者：
Maruoka, Keiji
中科院分区：
文献类型：
--
作者：
Ooi, Takashi;Fukumoto, Kazuhiro;Maruoka, Keiji
烯醇化物的直接烷基化反应是有机合成中形成碳-碳键的重要方法。在过去的三十年里，使用手性助剂的非对映选择性烷基化的概念在严格控制立体化学方面发挥了主导作用。对广泛的底物有用的系统的建立导致手性助剂在该领域中获得卓越的地位。[1]另一方面，尽管互补催化变体具有实际和根本的重要性，但它们的开发要少得多。[2]与最近出现的用于烯醇化物的不对称烯丙基化、[2，3]芳基化[2]和乙烯基化[4]的高效过渡金属催化方法相反，涉及sp3-杂化亲电试剂（例如烷基卤化物）的催化对映选择性烷基化的可靠方案仍然受到限制。[2，5，6]虽然手性相转移催化对这一领域做出了重大贡献，[2，6]这种策略的主要缺点是它仅对有限的底物池有效。特别地，它在获得具有季α-碳立体中心的高价值的对映体富集的羰基化合物方面具有有限的适用性。[7]我们解决这个大部分未解决的问题的方法利用3，5-二芳基恶唑烷-2，4-二酮2作为新的含氧底物，其在N-螺手性溴化季铵1 e作为催化剂的存在下在温和的相转移条件下进行高度对映选择性烷基化（方案1）。[8]这种底物-催化剂组合为广泛的叔α-羟基-α-芳基羧酸衍生物提供了一个新的和实用的入口。[9、10]
The direct alkylation of enolates is an important method for the formation of carbon–carbon bonds in synthetic organic chemistry. The concept of diastereoselective alkylation by using chiral auxiliaries has played a dominant role over the past three decades for rigorously controling the stereochemistry. The establishment of systems useful for a broad range of substrates has resulted in chiral auxillaries attaining a preeminent position in the field.[1] On the other hand, complementary catalytic variants have been much less developed despite their practical and fundamental importance.[2] In contrast to the recent emergence of highly efficient transition-metal-catalyzed processes for asymmetric allylations,[2, 3] arylations,[2] and vinylations [4] of enolates, reliable protocols for catalytic enantioselective alkylation involving sp3-hybridized electrophiles, such as alkyl halides, are still restricted.[2, 5, 6] Although chiral phase-transfer catalysis has made a significant contribution to this area,[2, 6] the major drawback of this strategy is that it is only effective for a limited pool of substrates. In particular it has limited applicability in accessing enantioenriched carbonyl compounds of high value which possess quaternary α-carbon stereocenters.[7] Our approach toward this largely unsolved problem utilizes 3, 5-diaryloxazolidin-2, 4-diones 2 as novel oxygen-containing substrates that undergo highly enantioselective alkylation under mild phase-transfer conditions in the presence of the N-spiro chiral quaternary ammonium bromide 1e as catalyst (Scheme1).[8] This substrate–catalyst combination provides a new and practical entry to a wide range of tertiary α-hydroxy-α-aryl carboxylic acid derivatives.[9, 10]