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À propos de : Solution Structure and Chelation Properties of 2-ThienyllithiumReagents        

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  • Solution Structure and Chelation Properties of 2-ThienyllithiumReagents
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  • The solution and chelation properties of 2-thienyllithium reagents with potential amine and etherchelating groups in the 3-position and related model systems have been investigated using lowtemperature 6Li, 7Li, 13C, and 31P NMR spectroscopy, 15N-labeling, and the effect of solvent additives.In THF−ether mixtures at low temperature 3-(N,N-dimethylaminomethyl)-2-thienyllithium (4) isca. 99% dimer (which is chelated) and 1% monomer (unchelated), whereas 3-(methoxymethyl)-2-thienyllithium (5) is <10% dimer. Compound 5 crystallizes as a THF-solvated dimer, but there isno indication that the ether side chain is chelated in solution. Both 4 and 5 form PMDTA-complexedmonomers almost stoichiometrically, similar to the model compound 2, in sharp contrast to phenylanalogues, which show very different behavior. The barriers to dimer interconversion are ca. 2kcal/mol lower and chelation is significantly weaker in the 2-thienyllithium reagents than in theirphenyl analogues.
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