Catalytic enantioselective 1,2-diboration of 1,3-dienes: versatile reagents for stereoselective allylation.
Catalytic enantioselective 1,2-diboration of 1,3-dienes: versatile reagents for stereoselective allylation.
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DOI：
10.1002/anie.201105716
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发表时间：
2012-01-09
影响因子：
16.6
通讯作者：
Morken, James P.
中科院分区：
文献类型：
--
作者：
Kliman, Laura T.;Mlynarski, Scott N.;Ferris, Grace E.;Morken, James P.
聚酮化合物是一类重要的天然产物，具有很强的生物活性和复杂的化学结构。在构建这些系综的方法中，烯丙基金属试剂[1]-特别是烯丙基硼试剂[2]-与前手性羰基的立体选择性加成特别突出。使用I型烯丙基化试剂[3]，该反应不仅提供了用于建立适当的氧化模式的策略性定位的功能，而且其立体化学可预测性允许随时获得乙酸酯，丙酸酯和异丁酸酯合成等同物。然而，许多烯丙基化反应的局限性在于它们提供带有末端烯烃的产物;如果需要烯烃上的额外取代或官能度，则通常需要额外的合成操作。[4]在这方面，乙烯基羟醛反应已被证明是特别重要的，因为它提供了烯酸酯衍生的高烯丙醇。不幸的是，即使非常重视催化对映体选择性乙烯基羟醛缩合反应的发展，一个有效的顺式选择性不对称丙酸酯的版本仍然是不可用的，因为是一个版本，提供季中心。[5]在这份报告中，我们文件的第一个例子的对映选择性催化1，3-二烯的1，2-二硼化反应（方程。1，方案1）。如方案1所示，1，3-二烯的1，2-二硼化提供了被完美地配置为参与高选择性烯丙基化反应的烯丙基硼试剂（1）。[6，7，8]重要的是，通过适当的氧化后处理，这些反应提供了直接解决上述合成限制的乙烯基羟醛当量。同样重要的结果是，烯丙基化产物2中的烯丙基硼可以进行其它有用的键形成反应[9]，其允许扩链聚酮化合物的合成。[10]本实验室最近的一项研究发现，Pt（dba）_3和手性亚膦酸酯配体可以实现反式-1，3-二烯的对映选择性1，4-二硼化反应。[11虽然替代磷供体的评估揭示了提供所需1，2二硼化的配体，但选择性是次优的。获得1，2-二硼化产物的更可靠的策略是用顺式1，3-二烯代替反式二烯底物。该方法在一系列底物上提供了1，2-二硼化产物（3：1至> 20：11，2：1，4选择性），并且通常以优异的对映体选择性发生。优化后，发现表1中所示的配体结构和反应条件是最佳的。关于聚丙酸酯合成，顺式-戊二烯的二硼化是最重要的，并且发现这以优异的对映选择性（95：5 er）和良好的产率与配体L2（1，表1）发生。[13]除了苯基取代的二烯，所有其他的顺式二烯检查时，采用配体L1与突出的antirocontrol反应。采用配体L3的1，1-二取代二烯的二硼化反应以均匀高水平的立体控制发生
Polyketides are an important class of natural products that often possess potent biological activity and intriguing chemical structures. Among the methods for constructing these ensembles, the stereoselective addition of allylmetal reagents [1]-particularly allyl boron reagents [2]-to prochiral carbonyls holds particular prominence. With Type I allylation reagents [3], this reaction not only delivers functionality that is strategically positioned for establishing appropriate oxygenation patterns, but its stereochemical predictability allows ready access to acetate, propionate, and isobutyrate synthetic equivalents. A limitation of many allylation reactions, however, is that they deliver products bearing a terminal alkene; if one desires additional substitution or functionality on the olefin, additional synthetic manipulations are often required.[4] In this regard, the vinylogous aldol reaction has proven particularly important as it delivers enoate-derived homoallylic alcohols. Unfortunately, even with the tremendous emphasis placed on the development of catalytic enantioselective vinylogous aldol reactions, an efficienct syn-selective asymmetric propionate version is still unavailable, as is a version that delivers quaternary centers.[5] In this report, we document the first examples of the enantioselective catalytic 1, 2-diboration of 1, 3-dienes (eq. 1, Scheme 1). As depicted in Scheme 1, the 1, 2-diboration of 1, 3-dienes delivers allylboron reagents (1) that are perfectly configured to participate in highly selective allylation reactions.[6, 7, 8] Importantly, with appropriate oxidative work-up, these reactions deliver vinylogous aldol equivalents that directly address the above-described synthesis limitations. Also of significant consequence, is that the allyl boron in the allylation product 2 may be subject to other useful bond forming reactions [9] that allow for chain-extending polyketide synthesis.To develop the catalytic synthesis strategy in Scheme 1, efforts were first extended toward the development of an enantioselective 1, 2-diboration of terminal dienes.[10] A recent study in our laboratory found that enantioselective 1, 4-diboration of trans-1, 3-dienes could be accomplished with Pt (dba) 3 and a chiral phosphonite ligand.[11, 12] While evaluation of alternate phosphorous donors revealed ligands that furnished the desired 1, 2 diboration, selectivity was suboptimal. A more reliable strategy for obtaining the 1, 2-diboration product was to replace the trans diene substrate with cis 1, 3-dienes. This approach furnished 1, 2-diboration products (3: 1 to> 20: 1 1, 2: 1, 4 selectivity) across a range of substrates and generally occured with excellent enantioselection. After optimization, the ligand structures and reaction conditions depicted in Table 1 were found to be optimal. With respect to polypropionate synthesis, the diboration of cis-pentadiene is paramount and this was found to occur in excellent enantioselectivity (95: 5 er) and good yield with ligand L2 (1, Table 1).[13] Aside from the phenyl substituted diene, all other cis dienes examined reacted with outstanding enantiocontrol when employing ligand L1. The diboration of 1, 1-disubstituted dienes employing ligand L3 occured with uniformly high levels of stereocontrol
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影响因子：
16.6
作者：
Binanzer, Michael;Fang, Guang Yu;Aggarwal, Varinder K.
通讯作者：
Aggarwal, Varinder K.
影响因子：
4.9
作者：
Das, Jaya Prakash;Marek, Ilan
通讯作者：
Marek, Ilan
影响因子：
15
作者：
Denmark, SE;Fu, JP
通讯作者：
Fu, JP
影响因子：
15
作者：
Burks HE;Kliman LT;Morken JP
通讯作者：
Morken JP
影响因子：
1.8
作者：
DENMARK, SE;WEBER, EJ
通讯作者：
WEBER, EJ