Enol silanes, nonstereogenic

Chiral a-methyl aldehydes (43) show exceptional diastereofacial preferences in their Lewis acid mediated reactions with enol silanes (equation i6) 2i 25c-26-64 selected data are reported in Table 8. The reason for this selectivity may be due to an approach trajectory of the nucleophile closer to the stereocenter when the carbonyl group is bound to the Lewis acid. Additions to chiral a-alkoxy aldehyde (48) were studied with both nonstereogenic (equation 17 Table 9) and stereogenic enol silanes (equation 18 Table 10). (Stereogenic and nonstereogenic are defined according to Mislow and Siegel.) ... 

With nonstereogenic enol silanes (Table 9) usually (not always, see entry 2) a single isomer was obtained using tin(IV) chloride or titanium chloride as a promoter (entries 3, 5, 7 and 9). This high facial... 

Table 9 Ratio of Diastereoisomers in the Reactions of Nonstereogenic Enol Silanes with Aldehyde...

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