Palladium-catalyzed α-arylation of esters and amides under more neutral conditions
Palladium-catalyzed α-arylation of esters and amides under more neutral conditions
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DOI：
10.1021/ja036792p
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发表时间：
2003-09-17
影响因子：
15
通讯作者：
Hartwig, JF
中科院分区：
文献类型：
--
作者：
Hama, T;Liu, XX;Hartwig, JF
本文报道了羰基化合物的α-芳基化反应的两种方法，其反应条件比芳基卤化物与碱金属烯醇化物的反应条件更中性。第一种方法依赖于开发带有受阻五苯基二茂铁基二叔丁基膦（Q-phos）和高反应性二聚Pd（I）络合物{P（t-Bu）3]PdBr}2的催化剂。通过这种方法，由α-溴代酯和酰胺制备的烯醇化锌与芳基卤化物反应，在温和的条件下，使用1 - 2 mol %的催化剂和显著的官能团耐受性，高产率地形成α-芳基酯和酰胺。通过第二个程序，甲硅烷基烯酮和甲硅烷基酮亚胺缩醛与芳基溴在亚化学计量的氟化锌、1摩尔% Pd（dba）2和2摩尔% P（t-Bu）3的存在下在DMF溶剂中在80 °C下反应。报道了乙酸叔丁酯和丙酸叔丁酯的烯醇化锌、丙酸叔丁酯和异丁酸甲酯的三甲基硅基乙烯酮缩醛与带有给电子基团和潜在反应活性的碱敏吸电子基团的芳基溴以及与吡啶基溴的反应。此外，非对映选择性偶联苯基溴与酰亚胺烯醇轴承埃文斯辅助报道，这项研究表明，外消旋碱敏感的立体中心不发生在这些更中性的条件下的偶联过程中。
Two procedures for the α-arylation of carbonyl compounds under conditions that are more neutral than those of reactions of aryl halides with alkali metal enolates are reported. The first procedure rests upon the development of catalysts bearing the hindered pentaphenylferrocenyl di-tert-butylphosphine (Q-phos) and the highly reactive dimeric Pd(I) complex {P(t-Bu)3]PdBr}2. By this procedure, zinc enolates prepared from α-bromo esters and amides react with aryl halides to form α-aryl esters and amides in high yields under mild conditions with 1−2 mol % catalyst and with remarkable functional group tolerance. By the second procedure, silyl ketene and silyl ketimine acetals react with aryl bromides in the presence of substoichiometric zinc fluoride, 1 mol % Pd(dba)2, and 2 mol % P(t-Bu)3in DMF solvent at 80 °C. Reactions of zinctert-butyl acetate and propionate enolates and trimethylsilyl ketene acetals oftert-butyl propionate and methyl isobutyrate with aryl bromides bearing electron-donating and potentially reactive, base-sensitive electron-withdrawing groups and with pyridyl bromides are reported. In addition, the diastereoselective coupling of phenyl bromide with an imide enolate bearing the Evans auxiliary is reported, and this study shows that racemization of base-sensitive stereocenters does not occur during the coupling process under these more neutral conditions.