2-Vinylindoles As the Four-Atom Component in a Catalytic [4+1] Cycloaddition with a Silylene-Palladium Species Generated from (Aminosilyl)boronic Ester

The palladium-catalyzed silylene transfer to 2-alkenylindoles from a silylboronic ester bearing a diethylamino group on the silicon atom takes place efficiently, resulting in the formation of a 1-sila-3-cyclopentene ring fused with the indole ring. Further silylene transfer proceeds in the reaction of 2-(1-alkenyl)indoles, giving bissilylated tricyclic indoles in high yields.