Asymmetric Photocycloadditions with an Optically Active Allenylsilane: Trimethylsilyl as a Removable Stereocontrolling Group for the Enantioselective Synthesis of exo -Methylenecyclobutanes

Allenylsilanes undergo enantioselective intramolecular photocycloaddition reactions with enones and enoates to give adducts in 76−99% enantiomeric excess and 67−90% yield. The silyl-substituted exo -methylenecyclobutane products undergo protodesilylation to give the parent unsubstituted exo -methylenecyclobutane. Optically active allenylsilanes may thus be used in enantioselective photocycloadditions in which the silyl moiety functions as a removable stereochemical controlling group.