Asymmetric synthesis of cyclic β-hydroxyallylsilanes via sequential allyltitanation-ring closing metathesis

Highly enantioenriched cyclic β-hydroxyallylsilanes have been prepared via enantioselective allylation of unsaturated aldehydes using a chiral allyltitanium reagent, followed by a ring-closing metathesis. Functionalized rings of various sizes have been synthesized and the electronic effect of the silicon group in the RCM reaction has been studied. The resulting cyclic β-hydroxyallylsilanes reacted stereoselectively with a variety of electrophilic reagents. A first application of this method to the synthesis of a highly functionalized dihydropyrane is reported.