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Homo‐ and Heterochiral Alkylzinc Fencholates: Linear or Nonlinear Effects in Dialkylzinc Additions to Benzaldehyde
Author(s) -
Steigelmann Melanie,
Nisar Yasmin,
Rominger Frank,
Goldfuss Bernd
Publication year - 2002
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/1521-3765(20021115)8:22<5211::aid-chem5211>3.0.co;2-s
Subject(s) - chemistry , diethylzinc , enantiopure drug , benzaldehyde , enantioselective synthesis , yield (engineering) , enantiomer , stereochemistry , chirality (physics) , catalysis , crystallography , medicinal chemistry , organic chemistry , materials science , nambu–jona lasinio model , chiral symmetry breaking , physics , quantum mechanics , quark , metallurgy
Scalemic mixtures of chiral anisyl fenchols with different ortho ‐substituents (X) in the anisyl moieties [X=H ( 1 ), Me ( 2 ), SiMe 3 ( 3 ) and t Bu ( 4 )] are employed as pre‐catalysts in enantioselective additions of diethylzinc to benzaldehyde. While a remarkable asymmetric depletion is apparent for X=H and Me, a linear relationship between the enantiomeric purity of the chiral source and the product 1‐phenylpropanol is observed for X=SiMe 3 and t Bu. X‐ray single crystal analyses show that racemic methylzinc fencholates obtained from 1 (X=H) and 2 (X=Me) yield homochiral dimeric complexes, while for 3 (X=SiMe 3 ) and 4 (X= t Bu) the heterochiral dimeric alkylzinc structures are formed. The enantiopure fenchols 1 – 4 all yield homochiral dimeric methylzinc complexes. Computed relative energies of homo‐ and heterochiral fencholate dimers with X=H and Me reveal an intrinsic preference for the formation of the homochiral dimers, consistent with the observed negative NLE. In contrast, similar stabilities are computed for homo‐ and heterochiral complexes of ligands 3 (X=SiMe 3 ) and 4 (X= t Bu), in agreement with the absence of a nonlinear effect for bulky ortho ‐substituents.