Simple, Stable, and Versatile Double-Allylation Reagents for the Stereoselective Preparation of Skeletally Diverse Compounds

A new and efficient class of double-allylation reagents, α-trimethylsilylmethyl allylboronate 1 and the crotylboronates 12, is reported. These stable bimetallic reagents are prepared easily in enantiomerically pure form and add under BF₃ catalysis onto a wide range of aldehydes to afford a direct access to hydroxyl-functionalized allylic silanes in very high E/Z selectivity and excellent enantioselectivity (up to 98% ee). The useful hydroxyl-functionalized allylsilane intermediates can be exploited in chemodivergent syntheses of various compound classes such as acyclic propionate units, polysubstituted furans, vinylcyclopropanes, and larger carbocycles.