Cobalt-catalyzed trimethylsilylmethylmagnesium-promoted radical alkenylation of alkyl halides: A complement to the heck reaction
Cobalt-catalyzed trimethylsilylmethylmagnesium-promoted radical alkenylation of alkyl halides: A complement to the heck reaction
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DOI：
10.1021/ja061417t
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发表时间：
2006-06-21
影响因子：
15
通讯作者：
Miyoshi, Katsuhiko
中科院分区：
文献类型：
--
作者：
Affo, Walter;Ohmiya, Hirohisa;Miyoshi, Katsuhiko
钴配合物[CoCl 2（dpph）]（DPPH = [1，6-双（二苯基膦基）己烷]）在醚中Me 3SiCH 2 MgCl存在下催化烷基卤的分子间苯乙烯化反应以产生β-烷基苯乙烯。包括烷基氯在内的各种烷基卤化物可参与苯乙烯化。强烈建议的苯乙烯化反应的自由基机制。环丙基甲基溴和6-溴-1-己烯的顺序异构化/苯乙烯化反应提供了自由基机理的证据。对钴配合物的晶体学和光谱学研究表明，反应开始是从富电子的（双膦）双（三甲基硅甲基）钴（II）配合物单电子转移，然后还原消除，生成1，2-双（三甲基硅基）乙烷和（双膦）钴（I）配合物。[CoCl 2（dppb）]（DPPB = [1，4-双（二苯基膦基）丁烷]）催化剂和Me 3SiCH 2 MgCl的组合通过自由基过程诱导6-卤代-1-己烯的分子内Heck型环化反应。另一方面，2-碘苯酚的异戊烯基醚的分子内环化将以类似于常规钯催化转化的方式进行。碳（sp（2））-卤素键的非自由基氧化加成钴分别验证了钴催化的交叉偶联反应的烯基卤化物与Me 3SiCH 2 MgCl的起始乙烯基卤化物的构型保留。钴催化的分子间自由基苯乙烯化反应的烷基卤化物被施加到立体选择性的变体。1-烷氧基-2-溴环戊烷衍生物的苯乙烯化提供反式-1-烷氧基-2-苯乙烯基环戊烷骨架，其中之一是光学纯的。
A cobalt complex, [CoCl2(dpph)] (DPPH = [1,6-bis(diphenylphosphino) hexane]), catalyzes an intermolecular styrylation reaction of alkyl halides in the presence of Me3SiCH2MgCl in ether to yield beta-alkylstyrenes. A variety of alkyl halides including alkyl chlorides can participate in the styrylation. A radical mechanism is strongly suggested for the styrylation reaction. The sequential isomerization/styrylation reactions of cyclopropylmethyl bromide and 6-bromo-1-hexene provide evidence of the radical mechanism. Crystallographic and spectroscopic investigations on cobalt complexes reveal that the reaction would begin with single electron transfer from an electron-rich (diphosphine) bis(trimethylsilylmethyl) cobalt(II) complex followed by reductive elimination to yield 1,2-bis(trimethylsilyl) ethane and a (diphosphine) cobalt(I) complex. The combination of [CoCl2(dppb)] (DPPB = [1,4-bis(diphenylphosphino) butane]) catalyst and Me3SiCH2MgCl induces intramolecular Heck-type cyclization reactions of 6-halo-1-hexenes via a radical process. On the other hand, the intramolecular cyclization of the prenyl ether of 2-iodophenol would proceed in a fashion similar to the conventional palladium-catalyzed transformation. The nonradical oxidative addition of carbon(sp(2))-halogen bonds to cobalt is separately verified by a cobalt-catalyzed cross-coupling reaction of alkenyl halides with Me3SiCH2MgCl with retention of configuration of the starting vinyl halides. The cobalt-catalyzed intermolecular radical styrylation reaction of alkyl halides is applied to stereoselective variants. Styrylations of 1-alkoxy-2-bromocyclopentane derivatives provide trans-1-alkoxy-2-styrylcyclopentane skeletons, one of which is optically pure.