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Increasing Enantioselectivities and Reactivities by Stereochemical Tuning: Fenchone‐Based Catalysts in Dialkylzinc Additions to Benzaldehyde
Author(s) -
Goldfuss Bernd,
Steigelmann Melanie,
Rominger Frank
Publication year - 2000
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(200005)2000:9<1785::aid-ejoc1785>3.0.co;2-0
Subject(s) - chemistry , benzaldehyde , diethylzinc , trimethylsilyl , oniom , catalysis , medicinal chemistry , yield (engineering) , organic chemistry , stereochemistry , enantioselective synthesis , materials science , metallurgy
Trimethylsilyl substitutions of the fenchyl alcohols [(1 R ,2 R ,4 S )‐ exo ‐(2‐Ar)‐1,3,3‐trimethylbicyclo[2.2.1]heptan‐2‐ol, Ar = 2‐methoxyphenyl ( 1 ) and Ar = 2‐(dimethylaminomethyl)phenyl ( 2 )] yield the chiral ligands 3 [Ar = 2‐methoxy‐3‐(trimethylsilyl)phenyl] and 4 [Ar = 2‐(dimethylaminomethyl)3‐(trimethylsilyl)phenyl]. Increased reactivities and enantioselectivities in diethylzinc additions to benzaldehyde are obtained from 3 (63% ee R ) and 4 (93% ee S ), relative to 1 (26% ee S ) and 2 (73% ee S ). X‐ray crystal structures of 3 and of its methylzinc complex 3‐Zn reveal out‐of‐plane bending of the methoxy groups as major geometrical consequences of the trimethylsilyl substitutions. Analyses of QM/MM ONIOM μ‐O transition‐structure models for 1 , 2 , 3 , and 4 show that trimethylsilyl‐induced distortions of methoxy and of dimethylaminomethyl groups explain the observed increased enantioselectivities.