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( R )‐1,2,2‐Triphenyl‐2‐(trimethylsiloxy)ethyl Propionate: anti‐Selective and Diastereofacially Selective Aldol Addition; Diastereoselective Silylation and Alkylation
Author(s) -
Sacha Hubert,
Waldmüller Delia,
Braun Manfred
Publication year - 1994
Publication title -
chemische berichte
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 0009-2940
DOI - 10.1002/cber.19941271020
Subject(s) - chemistry , aldol reaction , ketene , alkylation , silylation , propionate , acetal , medicinal chemistry , deprotonation , diastereomer , benzaldehyde , propionates , stereoselectivity , adduct , aldol condensation , organic chemistry , aldehyde , stereochemistry , catalysis , ion
The propionates ( R )‐5 and ( R )‐ 6 which are derived from the readily available chiral auxiliary reagent ( R )‐triphenylglycol ( 4 ) have been applied in stereoselective aldol reactions. Whereas the enolate 7 and the silyl ketene acetal 12 , both generated from the ester ( R )‐ 6 , display only moderate diastereoselectivity when treated with benzaldehyde, ß‐hydroxyesters 8b and 16a , b are formed in diastereomeric ratios up to 95:5 (ratio of the main product to the sum of all other stereoisomers) when the propionate ( R )‐ 5 is subsequently deprotonated, transmetalated into the zirconium enolate and allowed to react with aldehydes. Alkaline hydrolysis or reduction with LiAlH 4 enables the conversion of the adducts 8a and 16a