135789-40-1Relevant academic research and scientific papers
(R)-1,2,2-Triphenyl-2-(trimethylsiloxy)ethyl Propionate: anti-Selective and Diastereofacially Selective Aldol Addition; Diastereoselective Silylation and Alkylation
Sacha, Hubert,Waldmueller, Delia,Braun, Manfred
, p. 1959 - 1968 (2007/10/02)
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, β-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 LiAlH4 enables the conversion of the adducts 8a and 16a, b into the carboxylic acid 15a and the diols 17a, b, respectively, which are obtained in >95percent e.e.When the enolate 13 is treated with chlorotrimethylsilane, carbon silylation occurs so that the α-silyl propionate 18a is formed diastereoselectively.On the other hand, alkylations of the enolate 13 with primary alkyl halides display only moderate diastereoselectivities.The structures of the propionate 5, the α-silyl ester 18a, and the alkylation product 18b are proven unambiguously by crystal structure analyses. - Key Words: Aldol reaction / Chiral enolate / Mandelic acid
