Stereochemically divergent pathways for the allylation and crotylation reactions of anti- and syn-β-hydroxy-α-methyl aldehydes with allyl- and crotyltrifluorosilanes

Allylation and crotylation reactions of 2,3-anti-β-hydroxy-α-methyl aldehydes 10 and 11 with allyl and crotyltrifluorosilanes 2, 8 and 9 proceed with high selectivity via the bicyclic chelated transition states 3 and 30. In contrast, analogous allylation and crotylation reactions of the 2,3-syn- β-hydroxy-α-methyl aldehydes 12 and 13 with 2, 8 and 9 are generally less selective and proceed preferentially by way of the normal Zimmerman-Traxler transition states 6 and 32.