Jantzi Kevin L, Puckett Craig L, Guzei Ilia A, Reich Hans J
Department of Chemistry, University of Wisconsin, 1101 University Avenue, Madison, Wisconsin 53706, USA.
J Org Chem. 2005 Sep 16;70(19):7520-9. doi: 10.1021/jo050592+.
[reaction: see text] The solution and chelation properties of 2-thienyllithium reagents with potential amine and ether chelating groups in the 3-position and related model systems have been investigated using low temperature 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) is ca. 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 is no indication that the ether side chain is chelated in solution. Both 4 and 5 form PMDTA-complexed monomers almost stoichiometrically, similar to the model compound 2, in sharp contrast to phenyl analogues, which show very different behavior. The barriers to dimer interconversion are ca. 2 kcal/mol lower and chelation is significantly weaker in the 2-thienyllithium reagents than in their phenyl analogues.
[反应：见正文] 使用低温6Li、7Li、13C和31P核磁共振光谱、15N标记以及溶剂添加剂的影响，研究了在3位带有潜在胺和醚螯合基团的2-噻吩锂试剂以及相关模型体系的溶液和螯合性质。在低温下的四氢呋喃-醚混合物中，3-(N,N-二甲基氨基甲基)-2-噻吩锂(4)约99%为二聚体（已螯合），1%为单体（未螯合），而3-(甲氧基甲基)-2-噻吩锂(5)的二聚体含量小于10%。化合物5以四氢呋喃溶剂化的二聚体形式结晶，但没有迹象表明醚侧链在溶液中被螯合。4和5都几乎以化学计量比形成PMDTA络合单体，类似于模型化合物2，这与苯基类似物形成鲜明对比，苯基类似物表现出非常不同的行为。二聚体相互转化的能垒比苯基类似物低约2千卡/摩尔，并且2-噻吩锂试剂中的螯合作用明显较弱。
