Gold-catalyzed intermolecular hydroamination of allenes with arylamines and resulting high chirality transfer
Gold-catalyzed intermolecular hydroamination of allenes with arylamines and resulting high chirality transfer
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DOI：
10.1002/anie.200600331
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发表时间：
2006-01-01
影响因子：
16.6
通讯作者：
Yamamoto, Yoshinori
中科院分区：
文献类型：
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作者：
Nishina, Naoko;Yamamoto, Yoshinori
苯胺2a在四氢呋喃中的两个当量在308℃下顺利进行，相应的烯丙基胺3a以78%的产率得到(表1，条目1)。其他催化剂如AgI、CuI、CuII、PdII和PtII以及H+对氢胺化反应没有促进作用。在没有金催化剂的情况下，即使在508℃加热后也没有反应发生。阳离子金催化剂如[Ph3PAuCl]/AgOTf和AuBr3/AgOTf的使用使产物3a的产率较低。事实证明，单取代芳基和烷基联烯1b-1f是氢胺化反应的良好底物(表1，条目2-6)。立体结构庞大的丙二烯1G使3G的产量较低(表1，条目7)。1，3-二取代烯1h和1j(表1，条目8和10)显示出与单取代烯相当的反应活性(表1，条目1和5)；然而，1，1-二取代烯1i和1k表现出极低的反应活性(表1，条目9和11)。有趣的是，烯烃1m-1o的氢胺化反应进行得非常顺利，它带有由可变长度的碳链连接的烯烃部分(n=2-4，表1，条目13-15)。[17]然而，在n=1(烯丙烯，11)的情况下，烯烃的影响不显著(表1，条目12)。反应活性的提高可能是由于烯烃与金物种配位的结果，这将有助于使两种底物相互接触。为了进一步了解反应机理，我们研究了手性联烯的氢胺化反应(方案1)。(±)-1J与苯胺的氢胺化反应得到(±)-3J，产率为80%，ee为99%。类似地，使用邻位、间位和对甲基苯胺(CH3C6H4NH2)代替苯胺得到了相应的手性烯丙基胺，产率高，ee值高。(±)-1h与苯胺的氢胺化反应生成(±)-3h，产率为68%，ee为88%。值得注意的是，取代联烯的所有四个选择性问题(位置选择性、化学选择性、区域选择性和立体选择性)[18]都在(±)-3h的形成中得到了解决。这些结果强烈地表明，金-胺络合物形成，然后与丙二烯的加成反应如A(方案1)所示。如果AuBr3仅仅表现为Lewis酸，使得金中心将激活丙二烯的双键，而苯胺将从与金配位相反的面上攻击，那么将获得(+)-3H。如果以类似于钯催化的氢胺化反应的方式将金的π-烯丙基络合物作为关键中间体，则可以得到外消旋3H。
two equivalents of aniline 2a in THF proceeded smoothly at 308C, and the corresponding allylic amine 3a was obtained in 78% yield (Table 1, entry 1). Other catalysts, such as AgI, CuI, CuII, PdII, and PtII compounds as well as H+, did not promote the hydroamination at all. In the absence of the gold catalyst, no reaction occurred even after heating at 508C. The use of cationic gold catalysts such as [Ph3PAuCl]/AgOTf and AuBr3/AgOTf gave lower yields of the product 3a.[16] At high temperature (80–1208C), AuBr3 lost its catalytic activity. Monosubstituted aryl-and alkyl allenes 1b–1 f proved to be good substrates for the hydroamination (Table 1, entries 2–6). The sterically bulky allene 1g gave 3g in lower yield (Table 1, entry 7). The 1, 3-disubstituted allenes 1h and 1j (Table 1, entries 8 and 10) showed reactivities comparable to the monosubstituted allenes (Table 1, entries 1 and 5); however, the 1, 1-disubstituted allenes 1i and 1k exhibited extremely low reactivities (Table 1, entries 9 and 11). Interestingly, the hydroamination proceeded very smoothly with the allenes 1m–1o, which bear an olefin moiety tethered by a carbon chain of variable length (n= 2–4, Table 1, entries 13–15).[17] However, in the case of n= 1 (allylallene, 1l), the effect of the olefin was not remarkable (Table 1, entry 12). The enhancement of the reactivity may be a result of the coordination of the olefin to a gold species, which would help to bring the two substrates into contact with each other. To obtain further insight into the mechanism, the hydroamination was investigated with chiral allenes (Scheme 1). The hydroamination of (À)-1j with aniline gave (À)-3j in 80% yield with 99% ee. Similarly, the use of ortho-, meta-, and para-toluidine (CH3C6H4NH2) instead of aniline afforded the corresponding chiral allylic amines in good yields with high ee values. The hydroamination of (À)-1h with aniline produced (À)-3h in 68% yield with 88% ee. It should be noted that all four selectivity problems of substituted allenes (positional selectivity, chemoselectivity, regioselectivity, and stereoselectivity)[18] have been solved in the formation of (À)-3h. These results strongly suggest that a gold–amine complex is formed, and then the addition to the allene takes place as shown in A (Scheme 1). If AuBr3 behaved merely as a Lewis acid, such that the gold center would activate a double bond of the allene and the aniline would attack from the face opposite to gold coordination, then (+)-3h would have been obtained. If a gold π-allyl complex was involved as a key intermediate in a similar manner to that of the palladium-catalyzed hydroamination, racemic 3h would have been obtained.