STRUCTURE AND REACTIVITY OF LITHIATED ALPHA-AMINO NITRILES

Investigations aimed at elucidating the structure of Lithiated alpha-a mino nitriles B have led to the identification of N-Lithio alpha-amino nitrile anions as characteristic structural features, Their preparati ons, crystal structures, and solution structures under the reaction co nditions, are described, X-ray crystal structure analyses of crystalli ne 3 and (S,S)-4 reveal the presence of dimeric aggregates B4 with C-i symmetry, held together by four-membered NLiNLi rings, coordinatively saturated at lithium by four THF Ligands. The crystal structure of (S ,S)-6 shows polymeric aggregation with dimeric subunits similar to tho se of 3 and (S,S)-4. The solution structure has been investigated by I R and Raman spectroscopy of 2, (S,S)-4 and (S,S)-6, by NMR spectroscop y of 3, (S,S)-5 and (S,S)-6, and by cryoscopic measurements of (S,S)-6 in THF. Trapping experiments complement the results. In THE which con stitutes the principal reaction medium, the Lithiated amino nitriles B are found to exist as monomeric species B6 between -110 and +25(degre es)C, In less polar solvents, higher aggregation is presumed. NMR spec troscopic studies of 3 show that the favored orientations of the amine and phenyl groups are similar to their conformations in the solid sta te. In the light of the results obtained, a transition state is propos ed to account for the relative topicity observed in the 1,4-additions of enantiopure lithiated a-amino nitriles (S,S)-4, (S,S)-5, and (S,S)- 6 to Michael accepters.