Lanthanide complexes diastereofacial selectivity

J.2 The Effect of Lewis Acids on Diastereofacial Selectivity 2JJ2.1 Zinc chloride and lanthanide complexes... 

The use of ZnCh and (3-diketonate complexes of lanthanide metals give predominately endo-type addition products and CF diastereofacial selectivity. The CF stereoselectivity seems to prevail in cases using ZnCh as a catalyst and chiral aldehydes that contain groups that do not chelate to the metal. The selectivity clearly decreases when aldehydes that can form chelates are used. The lanthanide catalysts also exhibit strong CF-type selectivity with nonchelating chiral aldehydes. This trend seems to hold with most chelating aldehydes however, ACF products have been reported when a-alkoxy aldehydes are used in the reaction.56 The stereochemical consequences of using lanthanide catalysts with a-alkoxy aldehydes are therefore not predictable. 

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