PdII- and PtII-mediated polycyclization reactions of 1,5- and 1,6-dienes:: Evidence in support of carbocation intermediates
PdII- and PtII-mediated polycyclization reactions of 1,5- and 1,6-dienes:: Evidence in support of carbocation intermediates
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DOI：
10.1002/anie.200453913
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发表时间：
2004-01-01
影响因子：
16.6
通讯作者：
Gagné, MR
中科院分区：
文献类型：
--
作者：
Koh, JH;Gagné, MR
仿生聚烯烃级联反应[1，2]代表了反应设计中一些最具挑战性的问题，其产物在自然界中普遍存在。[3]由于Yamamoto等人的布朗斯台德-路易斯酸（BLA）是唯一已知的用于阳离子-烯烃环化的不对称催化引发的合成催化剂，[4，5]我们开始对替代的C12 C键形成级联感兴趣，其中末端烯烃的活化与亲电PdII源一起发生。虽然该过程不常见，但在用[PdCl 2（RCN）2]催化科普重排[Eq. (1)]作者Overman et al. [6]碎片的阳离子中间体在相反的regiodirection提出，以产生一个新的二烯和PdII复合物。最近，Wyndham hoefer et al. [7]和Toyota，Ihara et al. [8]证明亲核烯醇通过β-氢化物消除[9]或质子化产生碳环产物。[10]虽然取代基效应[11]和立体化学研究[6c]分别支持阳离子和环状中间体，但这种中间体的确切性质尚不清楚，并且缺乏这种阳离子的直接证据。[12]因此，我们启动了一项计划，首先收集支持碳环阳离子中间性的证据，同时确定它是否可以作为引发新金属介导反应的点。我们追求的关键是Vitagliano等人最近报道的吡啶基双膦钳形配体[Pt（PNP）]（BF 4）2（PNP= 2，6-双（二苯基膦基甲基）吡啶）的双阳离子Pt络合物，其催化乙烯和2-甲基-2-丁烯的二聚。[13，14] 2-甲基-2-丁烯与配位基的分子间亲核加成反应。
Biomimetic polyolefin cascade reactions [1, 2] represent some of the most challenging problems in reaction design, and their products are ubiquitous in the natural world.[3] Since the Brønsted–Lewis acids (BLAs) of Yamamoto et al. are the only known synthetic catalysts for asymmetric catalytic initiation of cation–olefin cyclizations,[4, 5] we became interested in an alternative CÀC bond-forming cascade wherein activation of a terminal alkene occurs with an electrophilic PdII source. Although this process is uncommon, it is precedented in the catalysis of the Cope rearrangement with [PdCl2 (RCN) 2][Eq.(1)] by Overman et al.[6] Fragmentation of a cationic intermediate in the opposite regiodirection was proposed to generate a new diene and a PdII complex. More recently, Widenhoefer et al.[7] and Toyota, Ihara et al.[8] demonstrated that nucleophilic enols lead to carbocyclic products by β-hydride elimination [9] or protonation.[10]Although substituent effects [11] and stereochemical studies [6c] support a cationic and cyclic intermediate, respectively, the exact nature of this intermediate is unclear, and direct evidence for this cation is lacking.[12] We therefore initiated a plan that first gathered evidence supporting the intermediacy of the carbocyclic cation, while also determining whether it could function as a point for initiating new metal-mediated reactivity. The key to our pursuit was a recent report by Vitagliano et al. of a dicationic Pt complex of a pyridyl bisphosphane pincer ligand [Pt (PNP)](BF4) 2 (PNP= 2, 6-bis (diphenylphosphanylmethyl) pyridine) that catalyzes the dimerization of ethylene and 2-methyl-2-butene.[13, 14] Intermolecular nucleophilic addition of 2-methyl-2-butene to coordi-