Preparation of σ- and π-Allylcopper(III) Intermediates in SN2 and SN2′ Reactions of Organocuprate(I) Reagents with Allylic Substrates

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• 作者：Erika R. Bartholomew ; Steven H. Bertz ; Stephen Cope ; Michael Murphy ; Craig A. Ogle
• 刊名：Journal of the American Chemical Society
• 出版年：2008
• 出版时间：August 27, 2008
• 年：2008
• 卷：130
• 期：34
• 页码：11244-11245
• 全文大小：159K
• 年卷期：v.130,no.34(August 27, 2008)
• ISSN：1520-5126

文摘

The first π-allyl complexes of Cu^III have been prepared and characterized by using rapid injection nuclear magnetic resonance spectroscopy (RI-NMR). The prototype, (η³-allyl)dimethylcopper(III), was prepared by injection of allyl chloride into a THF-d₈ solution of iodo-Gilman reagent, Me₂CuLi·LiI (A), spinning in the probe of an NMR spectrometer at −100 °C. A σ-allyl ate complex, lithium (η¹-allyl)trimethylcuprate(III), was prepared in high yield by including 1 equiv of tributylphosphine in the reaction mixture or by using allyl acetate as the substrate. Cyano ate complex, lithium cis-(η¹-allyl)cyanodimethylcuprate(III) was obtained in high yield by injecting allyl chloride or allyl acetate into the cyano-Gilman reagent, Me₂CuLi·LiCN (B), in THF-d₈ at −100 °C. Reactions of A with allylic substrates show a definite dependence on leaving group (chloride vs acetate), whereas those of B do not. Moreover, these reagents have different regioselectivities, which in the case of A vary with temperature. Finally, the exclusive formation of cis-cyano σ-allyl Cu^III intermediates in both the 1,4-addition of B to α-enones and its S_N2α reaction with allylic substrates now makes sense in terms of π-allyl intermediates in both cases, thus unifying the mechanisms of these two kinds of conjugate addition.