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| - Spectroscopic Characterization of (Iodomethyl)zinc ReagentsInvolved in Stereoselective Reactions: Spectroscopic EvidenceThat IZnCH2I Is Not Zn(CH2I)2 + ZnI2 in the Presence of anEther
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| - We have shown that low-temperature 13C NMRspectroscopy is an extremely powerful technique forcharacterizing the (iodomethyl)zinc-derived reagents involved inthe cyclopropanation reactions. This techniquehas allowed us to spectroscopically characterize and unambigouslydifferentiate the Furukawa reagent (EtZnCH2I),the Simmons−Smith reagent (IZnCH2I), and the Wittigreagent (Zn(CH2I)2). Unique spectraare obtained for eachof these reagents when they are complexed to a chiral diether. Wehave also demonstrated that IZnCH2I is notconverted into Zn(CH2I)2 + ZnI2in CD2Cl2 in the presence of a chiralcomplexing agent. Furukawa's reagent“EtZnCH2I”, however, is in equilibrium withEt2Zn and Zn(CH2I)2, andit eventually decomposes into PrZnI andEtZnI at room temperature. The decomposition ofZn(CH2I)2 into IZnCH2I and ofIZnCH2I into ZnI2 was monitoredby NMR. We have also demonstrated that the general trends observedfor the various equilibria involving(iodomethyl)zinc-derived reagents follow those observed withethylzinc-derived organometallic compounds.
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