Directed hydrozirconation of propargylic alcohols
Directed hydrozirconation of propargylic alcohols
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DOI：
10.1021/ja075215o
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发表时间：
2007-10-10
影响因子：
15
通讯作者：
Ready, Joseph M.
中科院分区：
文献类型：
--
作者：
Zhang, Donghui;Ready, Joseph M.
用CP_2ZrH（Cl）（Schwartz试剂）进行末端炔的锆氢化反应通常以高选择性进行以产生末端乙烯基锆。在标准锆氢化条件下，末端炔丙醇也不例外。然而，我们报告说，区域选择性的意义是完全逆转时，进行锆氢化锂醇盐的末端炔丙醇在氯化锌的存在下。仅观察到更受阻的支化产物。该反应容许甲硅烷基和烷基醚、芳族和杂芳族环，甚至末端烯烃和炔。中间体乙烯基有机金属试剂可以被12、烯酮和烯丙基溴捕获，并且可以直接参与交叉偶联反应。产物以良好的产率分离为单一区域异构体。我们提供的证据表明，氯化锌的存在下改变的动力学选择性，使内部产品是有利的。更重要的是，ZnCl2抑制乙烯基金属物质的异构化，可能是通过金属转移到乙烯基氯化锌。
Hydrozirconation of terminal alkynes with CP2ZrH(Cl) (Schwartz reagent) usually proceeds with high selectivity to yield the terminal vinyl zirconium. Under standard hydrozirconation conditions, terminal propargylic alcohols are no exception. However, we report that the sense of regioselectivity is completely reversed when the hydrozirconation is performed on the lithium alkoxide of terminal propargylic alcohols in the presence of ZnCl2. Only the more hindered, branched products are observed. The reaction tolerates silyl and alkyl ethers, aromatic and heteroaromatic rings, and even terminal olefins and alkynes. The intermediate vinyl organometallic reagent can be trapped with 12, enones, and allyl bromide and can participate directly in cross-coupling reactions. Products are isolated in good yields as single regioisomers. We provide evidence that the presence of ZnCl2 alters the kinetic selectivity such that the internal product is favored. More importantly, ZnCl2 inhibits isomerization of the vinyl metal species, likely through transmetalation to a vinyl zinc chloride.