Unusual Highly Regioselective Direct Aldol Additions with a Moisture-Resistant and Highly Efficient Titanium Catalyst
作者:Rainer Mahrwald、Bernd Schetter
DOI:10.1021/ol052637z
日期:2006.1.1
[reaction: see text] The extremely robust and water-stable tetranuclear complex Ti(4)(mu-BINOLato)(6)(mu(3)-OH)(4) was found to catalyze the direct aldol addition with high regioselectivities at the more steric alpha-encumbered side of unsymmetrical ketones. As few as 0.2 mol % loadings with this cluster were enough to afford complete conversions. The reaction proceeds very smoothly without a significant
the direct aldol addition with high degrees of regioselectivity at the sterically more encumbered α-side of unsymmetrical ketones. The formation of quaternary stereocenters is described. Oxygen-containing ene components can also be used as starting material in these reactions. When used with aliphaticaldehydes, acetals 18 or acetals of aldol adducts 20 were observed. As few as 0.2 mol % loadings with
α-Substituted-β-keto acid 2,2,2-trichloroethyl esters reacted with aldehydes regiospecifically at α-carbon to the ester carbonyl in the presence of Zn to give the corresponding aldols in good yields.