Evans Enolates: Solution Structures of Lithiated Oxazolidinone-Derived Enolates

The results of a combination of 6Li and 13C NMR spectroscopic and computational studies of oxazolidinone-based lithium enolatesEvans enolatesin tetrahydrofuran (THF) solution revealed a mixture of dimers, tetramers, and oligomers (possibly ladders). The distribution depended on the structure of the oxazolidinone auxiliary, substituent on the enolate, and THF concentration (in THF/toluene mixtures). The unsolvated tetrameric form contained a D 2d -symmetric core structure, whereas the dimers were determined experimentally and computationally to be trisolvates with several isomeric forms.