Catalytic Asymmetric Intramolecular Hydroacylation with Rhodium/Phosphoramidite-Alkene Ligand Complexes
Catalytic Asymmetric Intramolecular Hydroacylation with Rhodium/Phosphoramidite-Alkene Ligand Complexes
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DOI：
10.1002/anie.201104595
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发表时间：
2011-01-01
影响因子：
16.6
通讯作者：
Carreira, Erick M.
中科院分区：
文献类型：
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作者：
Hoffman, Thomas J.;Carreira, Erick M.
合理设计和开发含二烯烃[1,2]和膦-烯烃配体[3]的新型过渡金属催化剂，近年来在促进共轭和亚胺加成以及ynals环化等催化对映选择性反应方面受到了关注由膦-烯烃配体生成的杂电性配合物尤其有用，因为它们包括至少两种具有不同空间和电子性质的给体。在对映选择性烯丙基置换[3j， 6]和共轭加成[7]反应中，已经报道了以二苯并[b， f]氮平[5]为基序的膦烯-烯烃配体。随着对这些和相关配体类型的探索不断发展，它们在新工艺中的应用将会增加。在这里，我们报道了一个分子内不对称的铑催化的4-烯醛加氢酰化[8]反应，以制备环戊酮[Eq.(1)]。该催化体系的两个关键特征值得注意：这是首次将磷酰胺-烯烃配体用于该反应类型，并且非手性膦配体的加入对于促进对映选择性催化是必要的。1972年Sakai等人发表了开创性的报告[9]，其中使用了化学计量RhI， Miller等人[10]和Larock等人[11]表明，取代的g-pentenals使用[Rh (PPh3) 3Cl]进行了氢化环异构化。他们的方案特点是溶剂饱和乙烯和需要高催化剂负载（高达50 mol%）；此外，他们注意到竞争性脱碳途径形成了相当数量的副产物。Bosnich及其同事[12]和Sakai等人[13]独立报道了用binap或Me-DuPhos制备的阳离子高氯酸铑催化剂催化分子内对映选择性氢化反应这些研究表明，为了获得良好的产物选择性，二膦配体与五相底物的匹配是至关重要的。随后也进行了同位素标记研究，以阐明机理细节。[10,15]有人认为，早期报告中提到的乙烯在反应混合物中的好处是由于形成了一种稳定的抗分解的配位饱和阳离子铑。[10,11]使用乙烯的这一方面引起了我们的兴趣，并促使我们研究使用含有烯烃的供体配体。此外，我们设想了涉及原位生成异肽复合物的组合催化[16]的实现，正如Reetz等人，[17]Shibasaki及其同事，[18]和Ding及其同事的观察所表明的那样，这种方法是非常有益的在找矿实验中，我们考察了作为原型底物的pentenal 1a，在不同的反应条件下，由[{RhCl (C2H4) 2} 2]和磷酰胺配体(S)-L1[6]和（R， R， R）-L2[20]在AgI存在下原位生成配合物（表1）。这些反应条件不能产生环戊酮。有趣的是，将Ph3P （8mol %）引入到反应混合物中，其中包括(S)-L1 (8mol %),[{Rh (C2H4) 2}]（4mol %）和AgSbF6 (8mol %)，以52%的产率和66%的ee生成2a（表1，输入3）这一结果来自于一个涉及添加非手性配体的反应，这是有趣的，也是出乎意料的。相对于(S)-L1，加入第二等价物PPh3减慢了反应速度，导致对映体选择性降低（产率21%，ee 40%；表1，条目4）。当配体L2在类似的反应条件下进行反应时，没有观察到产物（表1，条目5）。在最初的…
The rational design and development of novel transitionmetal catalysts bearing diolefin [1, 2] and phosphine–olefin ligands [3] has recently gained attention for the promotion of catalytic enantioselective reactions such as conjugate and imine additions, as well as the cyclization of ynals.[4] The heteroleptic complexes generated from phosphine–alkene ligands can be particularly useful as they include at least two donors with distinct steric and electronic properties. Phosphine–alkene ligands featuring dibenzo [b, f] azepine [5] motifs have previously been reported in enantioselective allylic displacement [3j, 6] and conjugate addition [7] reactions. As the exploration of these and related ligand types continues to evolve, their use in novel processes will increase. Herein, we report an asymmetric intramolecular Rh-catalyzed hydroacylation [8] reaction of pent-4-enals for the preparation of cyclopentanones [Eq.(1)]. Two key features of the catalytic system are noteworthy: this is the first time phosphoramidite–alkene ligands have been used for this reaction type and the incorporation of an achiral phosphine coligand is necessary to promote enantioselective catalysis. After the seminal report in 1972 [9] by Sakai et al., in which stoichiometric RhI was used, Miller and co-workers [10] and Larock et al.[11] showed that substituted g-pentenals undergo hydroacylative cycloisomerization using [Rh (PPh3) 3Cl]. Their protocol featured solvent saturated with ethylene and necessitated high catalyst loading (up to 50 mol%); additionally, they noted the formation of considerable amounts of side products from competitive decarbonylation pathways. Bosnich and co-workers [12] and Sakai et al.[13] independently reported catalytic enantioselective intramolecular hydroacylation with cationic rhodium perchlorate catalysts prepared from binap or Me-DuPhos.[14] These studies showed that to obtain good product selectivity the matching of the diphosphine ligand to the pentenal substrates was of the utmost importance. Subsequent investigations with isotopic labelling have also been undertaken to shed light on the mechanistic details.[10, 15] It has been suggested that the benefits of ethylene in the reaction mixture, mentioned in the early reports, arise from the formation of a coordinatively saturated cationic rhodium species stabilized against decomposition.[10, 11] This aspect of using ethylene piqued our interest and led us to examine the use of donor ligands incorporating an olefin. Additionally, we envisioned the implementation of combinatorial catalysis [16] involving heteroleptic complexes generated in situ, an approach that is highly rewarding as illustrated by the observations of Reetz et al.,[17] Shibasaki and co-workers,[18] and Ding and co-workers.[19] In prospecting experiments we examined pentenal 1a, as the prototypical substrate, under various reaction conditions with complexes generated in situ from [{RhCl (C2H4) 2} 2] and phosphoramidite ligands (S)-L1 [6] and (R, R, R)-L2 [20] in the presence of AgI (Table 1). These reaction conditions failed to provide cyclopentanone. Interestingly, the introduction of Ph3P (8 mol%) into the reaction mixture, which included (S)-L1 (8 mol%),[{Rh (C2H4) 2}](4 mol%), and AgSbF6 (8 mol%), led to formation of 2a in 52% yield and 66% ee (Table 1, entry 3).[21] This result from a reaction involving the addition of an achiral ligand is intriguing and was unexpected. The inclusion of a second equivalent of PPh3, relative to (S)-L1, slowed the reaction and resulted in lower enantioselectivity (21% yield, 40% ee; Table 1, entry 4). When ligand L2 was tried under similar reaction conditions no product was observed (Table1, entry5). After the initial …