An Enantioselective Synthesis of Benzylidene-Protected syn-3,5-Dihydroxy Carboxylate Esters via Osmium, Palladium, and Base Catalysis
摘要:
[GRAPHICS]The enantioselective syntheses of several protected syn-3,5-dihydroxy carboxylic esters have been achieved from the corresponding achiral 1,3-dieneoates, The route relies upon an enantio- and regioselective Sharpless dihydroxylation and a palladium-catalyzed reduction to form delta -hydroxy-1-enoates, The resulting delta -hydroxy-1-enoates are subsequently converted into benzylidene-protected 3,5-dihydroxy carboxylic esters in one step, The benzylidene-protected 3,5-dihydroxy carboxylic esters are produced in good overall yields (25% to 51%) and high enantiomeric excesses (80% to >95%).
Lewis Base Activation of Lewis Acids: Catalytic, Enantioselective Addition of Silyl Ketene Acetals to Aldehydes
作者:Scott E. Denmark、Gregory L. Beutner、Thomas Wynn、Martin D. Eastgate
DOI:10.1021/ja047339w
日期:2005.3.1
The concept of Lewisbase activation of Lewisacids has been reduced to practice for catalysis of the aldolreaction of silyl ketene acetals and silyl dienol ethers with aldehydes. The weakly acidic species, silicon tetrachloride (SiCl4), can be activated by binding of a strongly Lewis basic chiral phosphoramide, leading to in situ formation of a chiral Lewisacid. This species has proven to be a competent
Lewis Base Activation of Lewis Acids. Vinylogous Aldol Reactions
作者:Scott E. Denmark、Gregory L. Beutner
DOI:10.1021/ja035448p
日期:2003.7.1
A highly regioselective vinylogous aldol reaction catalyzed by SiCl4 and a chiral phosphoramide (R,R)-5, providing delta-hydroxy enones for a variety of aldehyde and dienol ether structures, has been developed. Low catalyst loadings (1 mol %) can be employed, giving the products in good yields, excellent enantioselectivities, and in some cases excellent anti diastereoselectivities. Both simple ester-derived