Nickel-catalyzed asymmetric α-arylation and heteroarylation of ketones with chloroarenes: effect of halide on selectivity, oxidation state, and room-temperature reactions.
Nickel-catalyzed asymmetric α-arylation and heteroarylation of ketones with chloroarenes: effect of halide on selectivity, oxidation state, and room-temperature reactions.
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DOI：
10.1021/ja2082087
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发表时间：
2011-10-19
影响因子：
15
通讯作者：
Hartwig, John F.
中科院分区：
文献类型：
--
作者：
Ge, Shaozhong;Hartwig, John F.
本文报道了Ni（COD）_2和（R）-BINAP催化烯醇酮与一系列芳基氯的α-芳基化反应，对映选择性为90%~ 99%，Ni（COD）_2和（R）-DIFUROPHOS催化烯醇酮与一系列杂芳基氯的偶联反应，对映选择性高达99%。与卤代芳烃的典型相对反应性相反，溴代芳烃的类似反应以低得多的速率和对映选择性发生。机理研究表明，溴化和氯化芳基镍配合物[（R）-BINAP]Ni（X）（Ar）（X = Br和Cl）与2-甲基-1-茚满酮烯醇化钠的化学计量反应均能得到ee>99%的α-芳基茚满酮产物，尽管两种芳基卤代物的催化反应具有不同的对映选择性。[（R）-BINAP]Ni（X）（Ar）的分解产物{[（R）-BINAP] Ni（μ-X）}2催化酮的α-芳基化反应，其反应速率和对映选择性均低于Ni（COD）2和（R）-BINAP.因此，芳基卤化镍络合物的分解速率的差异可能解释了溴代芳烃和氯代芳烃的反应的对映选择性的差异。这种催化剂分解可以通过与Ni（0）物质[（R）-BINAP]Ni（η2-NC-Ph）（4）进行反应来克服，其在室温下添加卤代芳烃。该配合物催化的α-芳基化反应在室温下进行，对氯代芳烃和溴代芳烃的反应都具有较高的产率和对映选择性。
We report the α-arylation of ketone enolates with a range of aryl chlorides with enantioselectivities from 90% to 99% catalyzed by the combination of Ni(COD)2 and (R)-BINAP, and the coupling of ketone enolates with a range of heteroaryl chlorides with enantioselectivities up to 99% catalyzed by Ni(COD)2 and (R)-DIFLUORPHOS. In contrast to the typical relative reactivities of haloarenes, the analogous reactions of bromoarenes occur with much lower rates and enantioselectivities. Mechanistic studies showed that the stoichiometric reactions of both arylnickel bromide and chloride complexes [(R)-BINAP]Ni(X)(Ar) (X = Br and Cl) with the sodium enolate of 2-methyl-1-indanone afforded the α-aryl indanone product with >99% ee, even though the catalytic reactions of the two types of aryl halides occurred with much different enantioselectivity. Monitoring the enantioselectivity vs time showed that the reactions of aryl chlorides occurred with constant high ee, while the reactions of aryl bromides occurred with decreasing ee. The decomposition products of [(R)-BINAP]Ni(X)(Ar), {[(R)-BINAP]Ni(μ-X)}2, catalyze the α-arylation of ketones with slower rates and lower enantioselectivities than does Ni(COD)2 and (R)-BINAP. Therefore, the difference in rate of decomposition of the arylnickel halide complexes likely accounts for the difference in the enantioselectivities of the reactions of bromoarenes and chloroarenes. This catalyst decomposition can be overcome by conducting the reactions with the Ni(0) species, [(R)-BINAP]Ni(η2-NC-Ph) (4), which adds haloarenes at room temperature. α-Arylations catalyzed by this complex occur at room temperature with high yields and enantioselectivities for a wide range of both chloro- and bromoarenes.
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