Asymmetric Auto-Tandem Catalysis with a Planar-Chiral Ruthenium Complex: Sequential Allylic Amidation and Atom-Transfer Radical Cyclization
Asymmetric Auto-Tandem Catalysis with a Planar-Chiral Ruthenium Complex: Sequential Allylic Amidation and Atom-Transfer Radical Cyclization
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DOI：
10.1002/anie.201300485
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发表时间：
2013-01-01
影响因子：
16.6
通讯作者：
Onitsuka, Kiyotaka
中科院分区：
文献类型：
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作者：
Kanbayashi, Naoya;Takenaka, Kazuhiro;Onitsuka, Kiyotaka
具有多个立体中心的复杂分子的高效合成是有机合成化学中的一个具有挑战性的任务。一锅法反应由于可以避免耗时的后处理和中间产物的分离而受到广泛关注。[1]一个典型的例子是多米诺催化，其中两个或多个机械相似的反应在一个操作中进行。[1，2]另一种方法，自动串联催化也是一种理想的生态友好的合成方法，它涉及两个或更多个仅由单一催化剂促进的机械上不同的反应。[3]尽管有许多多米诺催化的例子，但关于自动串联催化的报道数量有限[4]，这可能是由于优化反应条件的困难。我们已经表明，平面手性环戊二烯基钌（Cp'Ru）配合物1是一个熟练的催化剂不对称烯丙基取代。[5，6]最近，我们成功地开发了单取代烯丙基卤化物与氧亲核试剂的区域选择性和对映选择性反应，该反应以良好的产率产生了对映体富集的支链烯丙基醚，酯和醇。[7]这些产物具有反应性末端烯烃，其可以潜在地应用于进一步转化。[7d，8]由于1的催化活性被保留，即使在烯丙基取代的末端，[7 b]并且钌络合物显示出催化行为的各种期望的氧化态，[9]我们设想将我们的系统扩展到自动串联不对称催化。作为一个候选人的终端烯烃上的支链烯丙基化合物的转化，我们专注于原子转移自由基环化（ATRC），因为半夹心钌配合物类似于1是已知的，以促进这一反应。[10]ATRC是一种原子经济的环状化合物的形成方法，它在温和的条件下进行，并表现出广泛的官能团耐受性。因此，我们假设配合物1可以实现由烯丙基取代和ATRC组成的不对称自动串联催化。为了验证这一理论，我们设想了光学活性的g-内酰胺的简单合成，这是在各种生物活性分子中发现的重要结构基序。[11]Nagashima及其同事报道了使用Ru催化剂的支链烯丙基酰胺的ATRC反应进行非对映选择性，[12，13]其中在新的立体碳上的构型由底物的立体化学控制。因此，通过1-催化的对映选择性烯丙基酰胺化制备光学活性烯丙基酰胺将通过1-催化的ATRC提供纯形式的具有多个立体中心的g-内酰胺（方案1）。在此我们报告
The efficient synthesis of complex molecules with multiple stereogenic centers is a challenging task in synthetic organic chemistry. One-pot reactions have received considerable attention for the improvement of reaction efficiency, because they can avoid time-consuming workups and the often formidable isolation of intermediary products.[1] A representative example is domino catalysis, in which two or more mechanistically similar reactions proceed in only one operation.[1, 2] Another method, auto-tandem catalysis is also an ideal and eco-friendly synthetic process, which involves two or more mechanistically distinct reactions promoted by only a single catalyst.[3] Despite numerous examples of domino catalysis, there are limited numbers of reports on autotandem catalysis,[4] this is probably due to the difficulty of optimizing the reaction conditions. We have shown that planar-chiral cyclopentadienylruthenium (Cp’Ru) complex 1 is a proficient catalyst for asymmetric allylic substitutions.[5, 6] Recently, we succeeded in the development of regio-and enantioselective reactions of monosubstituted allylic halides with oxygen nucleophiles, which produced enantiomerically enriched branched allylic ethers, esters, and alcohols in good yields.[7] These products possess a reactive terminal olefin, which can be potentially applied in a further transformation.[7d, 8] As the catalytic activity of 1 is preserved, even at the end of the allylic substitution,[7b] and ruthenium complexes show various desirable oxidation states for catalytic behavior,[9] we conceived an extension of our system to auto-tandem asymmetric catalysis. As a candidate for the transformation of a terminal olefin on a branched allylic compound, we focused on the atomtransfer radical cyclization (ATRC) because half-sandwiched Ru complexes similar to 1 are known to promote this reaction.[10] ATRC is an atom-economical method for the formation of cyclic compounds, which proceeds under mild conditions and exhibits broad functional group tolerance. Hence, it was hypothesized that complex 1 could realize an asymmetric auto-tandem catalysis consisting of allylic substitution and ATRC.To test this theory, we envisioned the facile synthesis of optically active g-lactams, an important structural motif found in a variety of biologically active molecules.[11] Nagashima and co-workers reported that ATRC reaction of branched allylic amides using a Ru catalyst proceeded diastereoselectively,[12, 13] with the configuration at the new stereogenic carbon controlled by the stereochemistry of the substrate. The preparation of optically active allylic amides by 1-catalyzed enantioselective allylic amidation would therefore provide g-lactams with multiple stereogenic centers in a pure form through 1-catalyzed ATRC (Scheme 1). Herein, we report