SPECTROSCOPIC CHARACTERIZATION OF (IODOMETHYL)ZINC REAGENTS INVOLVED IN STEREOSELECTIVE REACTIONS - SPECTROSCOPIC EVIDENCE THAT IZNCH2I IS NOT ZN(CH2I)(2)+ZNI2 IN THE PRESENCE OF AN ETHER

We have shown that low-temperature C-13 NMR spectroscopy is an extreme ly powerful technique for characterizing the (iodomethyl)zinc-derived reagents involved in the cyclopropanation reactions. This technique ha s allowed us to spectroscopically characterize and unambigously differ entiate the Furukawa reagent (EtZnCH(2)I), the Simmons-Smith reagent ( IZnCH2I), and the Wittig reagent (Zn(CH2I)(2)). Unique spectra are obt ained for each of these reagents when they are complexed to a chiral d iether. We have also demonstrated that IZnCH2I is not converted into Z n(CH2I)(2) + ZnI2 in CD2Cl2 in the presence of a chiral complexing age nt. Furukawa's reagent ''EtZnCH(2)I'', however, is in equilibrium with Et(2)Zn and Zn(CH2I)(2), and it eventually decomposes into PrZnI and EtZnI at room temperature. The decomposition of Zn(CH2I)(2) into IZnCH 2I and of IZnCH2I into ZnI2 was monitored by NMR. We have also demonst rated that the general trends observed for the various equilibria invo lving (iodomethyl)zinc-derived reagents follow those observed with eth ylzinc-derived organometallic compounds.