Using a temporary silicon connection in stereoselective allylation with allylsilanes: application to the synthesis of stereodefined 1,2,4-triols.

[reaction: see text]. Treatment of aldehyde 6 with TMSOTf, in the presence of a Brønsted acid scavenger, effects an intramolecular allylation to provide the oxasilacycle 7 as the major diastereoisomer. Tamao oxidation of the C-Si bond in 7 affords the corresponding 1,2,4-triol 9.