Pinacolone enolsilane

The nucleophilic addition of pinacolone enolsilane 1 to 5j -a-methyl-P-alkoxy aldehydes 2, promoted by Lewis acids, is highly stereoselective. Thus, when SnCU was employed, aldols 3 were obtained preferentially with selectivities higher than 95 5. Instead, the stereoisomers 4 were isolated with nearly total stereoselectivity when Mc2A1C1 (2 eq) was used to promote the reaction (Scheme 19. la and b). ... 

The stereoselectivity of the addition of pinacolone enolsilane 1 to P-alkoxy aldehydes bearing two stereocenters depends on the ability of the metal to form intermediate chelates. Those metals that monocoordinate the carbonyl group form Fel-kin products and the stereochemistry of these aldols is predicted by the Felkin-Anh s model. For metals chelating both the carbonyl and alkoxy groups, anti-Felkin products are obtained. In these cases the cyclic-Cram s model has to be used to predict the stereochemical outcome of the reaction. Therefore, non-chelated (Felkin-Ahn) and chelated models (cyclic-Cram) have been successively applied to understand the stereochemistry of the final reaction products. 

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See also in sourсe #XX -- [ , ]

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