Solid-State Structures and Racemization of Lithiated Schollkopf's Bis[Lactim Ether]

Addition of the respective Lewis base donors PMDTA and HMPA to lithiated Schollkopf's bis[lactim ether] (=3,6-diethoxy-2,5-dihydro-2-isopropylpyrazine) results in the formation of the monomeric PMDTA complex (R)-(4) (P212121, orthorhombic) and the dimeric HMPA complex (R,S)-3 (P, triclinic), as determined by single-crystal X-ray crystallography. Complex 3 was always found in racemic form, while complex 4 was enantiomerically pure. The racemization process that leads to the HMPA complex (R,S)-3 was investigated and found to be independent of the temperature at which either lithiation or addition of the Lewis base occurs.