One-Pot Three-Component Catalytic Enantioselective Synthesis of Homoallylboronates
One-Pot Three-Component Catalytic Enantioselective Synthesis of Homoallylboronates
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DOI：
10.1002/anie.201105458
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发表时间：
2011-01-01
影响因子：
16.6
通讯作者：
Cordova, Armando
中科院分区：
文献类型：
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作者：
Ibrahem, Ismail;Breistein, Palle;Cordova, Armando
富含对映体的α-手性有机硼化合物的合成在化学合成中受到了极大的关注，因为C±B键可以以立体专一性的方式转化为C±O、C±N和C±C键。[1]因此，设计高效的不对称合成含硼化合物的催化方案对有机合成非常有意义。[2，3]在这种情况下，高烯丙基和烯丙基的硼酸酯是非常有用的，因为利用烯基和硼基团的额外衍生化可以快速地获得多官能团的手性化合物。它们还可以作为手性亲核剂，分别用于醛和酮的加成，或亚胺的加成，以得到相应的醇或胺。[1b1金属催化的烯烃对映体选择性氢化是制备手性有机硼化合物的重要方法。[3]在合成对映富集烯丙基硼酸酯方面，Ito和他的同事公开了一种通过铜催化的1，3-二烯的区域选择性不对称单硼化反应合成对映富集烯丙基硼酸酯的方法。1)。[4]B_2Pin2(1)也被成功地用作手性膦铜配合物[5]或双齿N-四环卡宾铜络合物的硼基试剂，催化[6]与α，β-不饱和羰基化合物、烯烃、炔烃和二烯的对映选择性共轭加成。然而，据我们所知，1到2，4-二烯醇酸酯的区域选择性和对映体选择性的1，6-加成得到相应的高烯丙基硼烷4的反应尚未公开(关于结构见公式(1))。[7]该反应具有挑战性，更有可能生成1，4-加成产物B或两者的混合物。事实上，以PPh_3(7a)为配体进行铜催化1与苯基-2，4-二烯醇酸A的加成反应，2小时后只得到1，4-加成产物B(50%转化率，45%产率)[式(1)]。化学合成中的多组分反应是化学合成中的一个重要研究领域。特别是催化不对称多组分反应的发展是一项艰巨的任务。[8]基于发现新的对映选择性多组分反应的重要性，我们设想了一种替代路线，通过一锅催化不对称硼烷共轭加成/维蒂希反应序列，使用1，α，β-不饱和醛2，2-(三苯基亚磷酰亚甲基)乙酸酯3[式(2)]合成对映体富集烯丙基硼酸酯4。
The synthesis of enantioenriched α-chiral organoboron compounds has received significant attention in chemical synthesis because the CÀB bond can be converted into CÀO, CÀ N, and CÀC bonds in a stereospecific fashion.[1] Thus, the design of efficient catalytic protocols for asymmetric synthesis of boron-containing compounds is of utmost interest for organic synthesis.[2, 3] In this context, homoallyl-and allylboronates are highly useful since additional derivatization using the alkene moiety as well as the boron group gives rapid access to multifunctional chiral compounds. They can also be used as chiral nucleophiles for additions to either aldehydes and ketones, or imines to give the corresponding alcohols or amines, respectively.[1b1 The metal-mediated enantioselective hydroboration of alkenes is an important method for the preparation of chiral organoboron compounds.[3] With respect to the synthesis of enantioenriched homoallylboronates, Ito and co-workers disclosed an elegant protocol for the synthesis of enantioenriched cyclic homoallylboronates by coppercatalyzed regioselective asymmetric monoborylation of 1, 3-dienes using bis (pinacolato) diboron (B2pin2; 1).[4] B2pin2 (1) has also been successfully employed as the boryl reagent in chiral copper phosphine complexes [5] or bidentate N-hetrocyclic carbene copper complexes to catalyze [6] enantioselective conjugate additions to α, β-unsaturated carbonyl compounds, alkenes, alkynes, and dienes. However, the regioselective and enantioselective 1, 6-addition of 1 to 2, 4-dienaote esters such as A to give the corresponding homoallylboranes 4 has, to the best of our knowledge, not been disclosed (see Eq.(1) for structures).[7] This reaction is challenging and is more likely to render the 1, 4-addition product B or a mixture of both compounds. In fact, performing the copper-catalyzed addition of 1 to phenyl-2, 4-dienaote A using PPh3 (7a) as the ligand gave exclusively the 1, 4-addition product B after 2 hours (50% conv., 45% yield)[Eq.(1)].Multicomponent reactions that involve the formation of multiple CÀC and carbon–heteroatom bonds in a highly chemo-and stereoselective fashion in one pot is an important research field within chemical synthesis. In particular, the development of catalytic asymmetric multicomponent reactions is a difficult task.[8] Based on the importance of discovering new enantioselective multicomponent reactions, we envisioned an alternative route to the enantioenriched homoallylboronates 4 by a one-pot catalytic asymmetric borane conjugate addition/Wittig reaction sequence using 1, the α, β-unsaturated aldehydes 2, and 2-(triphenylphosphoranylidene) acetate esters 3 [Eq.(2)].