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Structure and Reactivity of Lithiated α‐Amino Nitriles
Author(s) -
Enders Dieter,
Kirchhoff Jochen,
Gerdes Peter,
Mannes Dietrich,
Raabe Gerhard,
Runsink Jan,
Boche Gernot,
Marsch Michael,
Ahlbrecht Hubertus,
Sommer Horst
Publication year - 1998
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/(sici)1099-0690(199801)1998:1<63::aid-ejoc63>3.0.co;2-h
Subject(s) - chemistry , reactivity (psychology) , nitrile , organic chemistry , combinatorial chemistry , computational chemistry , stereochemistry , medicine , alternative medicine , pathology
Investigations aimed at elucidating the structure of lithiated α‐amino nitriles B have led to the identification of N ‐lithio α‐amino nitrile anions as characteristic structural features. Their preparations, crystal structures, and solution structures under the reaction conditions, are described. X‐ray crystal structure analyses of crystalline 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 those of 3 and ( S, S )‐ 4 . The solution structure has been investigated by IR and Raman spectroscopy of 2 , ( S, S )‐ 4 and ( S, S )‐ 6 , by NMR spectroscopy 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 THF, which constitutes the principal reaction medium, the lithiated amino nitriles B are found to exist as monomeric species B6 between −110 and +25°C. In less polar solvents, higher aggregation is presumed. NMR spectroscopic studies of 3 show that the favored orientations of the amine and phenyl groups are similar to their conformations in the solid state. In the light of the results obtained, a transition state is proposed to account for the relative topicity observed in the 1,4‐additions of enantiopure lithiated α‐amino nitriles ( S, S )‐ 4 , ( S, S )‐ 5 , and ( S, S )‐ 6 to Michael acceptors.