Structure of a solvated nickel(II) complex of (S)-2'-(N-benzylprolyl)aminoacetophenone and (R)-valine Schiff base, C25H29N3NiO3.1/2C4H8O. Conformational calculation of diastereomeric complexes of (R)-valine and (S)-valine

Enantioselectivity in Ni(ii) Schiff-base complexes derived from amino-acids and (S)-o-N-(N-benzylprolyl)aminobenzophenone. Molecular structure of several chiral Ni(ii) Schiff-base complexes, circular dichroism and molecular mechanics studies

“…)]} = 32.6 kJ mol −1 , this being in agreement with the higher stability for the [Ni((S)-BBP-L-aa)] complexes. These values are significantly higher than those previously estimated for the [Ni((S)-BAPaa)] complexes, 29 this being a reasonable result as in BBP there is one phenyl group instead of the methyl group present in BAP. However, the differences are higher than those expected from the diastereomeric ratios found in the synthetic procedures, where entropic contributions, solvation, etc.…”

“…[Ni((S)-BAP-L-Val)] and [Ni((S)-BAP-D-Val)] it was estimated by MM calculations as 2.5 kJ mol −1 , and the barrier to rotation of the benzyl group around the N(3)-C( 6) bond was estimated not to exceed 21 kJ mol −1 for the same molecules. 29 In order to better understand the stereoselective effects in the formation of the several complexes molecular mechanics (MM) calculations were carried out using the Universal Force Field (UFF), 33 within the CERIUS2 software. 34 MM calculations can shed some light on the thermodynamics of the stereoselective effects, but it must be emphasized that our and previous MM calculations apply to the gas-phase structures, i.e., entropic contributions, solvation, ion-pairing, intermolecular H-bonding and electrostatic effects were not taken into account, as is often done for coordination compounds.…”

Productive Asymmetric Synthesis of All Four Diastereomers of 3‐(trans‐2‐Nitrocyclopropyl)alanine from Glycine with (S)‐ or (R)‐2‐[(N‐Benzylprolyl)amino]benzophenone as a Reusable Chiral Auxiliary

“…The molecular geometries of the nickel complexes derived from the chiral auxiliary 6 have been studied intensively along with the development of this method for the synthesis of enantiomerically pure α‐amino acids 10,11. It was shown,16 that the conformationally most labile parts of the molecule are the benzyl group and the five‐membered ring of the proline moiety, while the coordination around the nickel atom is more constant. In all four cases of the diastereomers 9abde the slightly distorted square coordination of Ni atoms remains virtually identical (Figure 2, A ) and only the conformations of the side chains differ slightly.…”

Synthesis of enantio- and diastereoiso-merically pure substituted prolines via condensation of glycine with olefins activated by a carbonyl group

“…cis-4-Methyl-(S)-proline was obtained in 74% yield (0.08 g, 0.59 mmol) from (12); m.p. 229-231 "C (lit.,6" 23&-231 "C); x~~~ 2 5 (3.5 (14) or (13).-Compound (12) was decomposed as already described to give the acid Condensution of the Complex (1) with Acrylaldehyde in the Presence of Sodium Methoxide at 25 "C.-To the complex (1) (0.25 g, 0.25 mmol) in NaOMe (2 ml; 1.2 mol dm-,), a solution of acrylaldehyde (0.03 ml, 0.45 mmol) in MeOH (1 ml) was added. After the complex (1) had been consumed (t.l.c.…”