| Abstract
| - The consequences of double diastereodifferentiation in chiral Lewis base catalyzed aldol additionsusing chiral enoxysilanes derived from lactate, 3-hydroxyisobutyrate, and 3-hydroxybutyrate havebeen investigated. Trichlorosilyl enolates derived from the chiral methyl and ethyl ketones weresubjected to aldolization in the presence of phosphoramides, and the intrinsic selectivity of theseenolates and the external stereoinduction from chiral catalyst were studied. In the reactions withthe lactate derived enolate, the strong internal stereoinduction dominated the stereochemicaloutcome of the aldol addition. For the 3-hydroxyisobutyrate- and 3-hydroxybutyrate derived enolates,the catalyst-controlled diastereoselectivities were observed, and the resident stereogenic centersexerted marginal influence. The corresponding trimethylsilyl enol ethers were employed in SiCl4/bisphosphoramide catalyzed aldol additions, and the effect of double diastereodifferentiation wasalso investigated. The overall diastereoselection of the process was again controlled by the strongexternal influence of the catalyst.
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