ORGN 267 |
| Several attributes of metalation chemistry, particularly for DoM, are ascribed to prior complexation of an alkyllithium reagent by either oxygen or nitrogen. Although such complexation has often been inferred, its detection has remained elusive. By use of hydrocarbon media, complexation by equivalents of THF, as in (n-BuLi)2•(THF)1-4 and by directing aryl-bonded methoxy groups, as in Ar(OMe)2•(n-BuLi)2 can be demonstrated utilizing 13C NMR at room temperature. In each case, distinct separate shifts of complexed and uncomplexed 13C signals have been resolved. Using this same 13C method, the half-life of equivalents of THF in hydrocarbon solvent is shown to be much longer than the published half-life of n-BuLi in neat THF. In certain substituted anisoles, the detection of enhanced complexation has been found to lead to increased rate and extent of ortho-lithiation. Lastly, attempts to demonstrate similar N-complexation (TMEDA, dimethylaniline, etc.) have been unsuccessful, at least at room temperature. |
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Metal-Mediated Reactions and Syntheses
1:00 PM-5:00 PM, Monday, 29 August 2005 Washington DC Convention Center -- 202B, Oral
Division of Organic Chemistry |