An Efficient Approach to Regio‐ and Stereodefined Fully‐Substituted Alkenylsilanes by Pd‐Catalyzed Allenic C(sp 3 )−H Oxidation

A highly efficient palladium‐catalyzed functionalization of allenylsilanes to give regio‐ and stereodefined fully‐substituted alkenylsilanes has been developed. This oxidative coupling reaction showed good functional group compatibility with exclusive regio‐ and stereoselectivity. The pending olefin on the silyl group was shown to be an indispensable element for the initial allenic C(sp 3 )−H bond cleavage, and performs as the directing group to control the overall selectivity. The addition of substoichiometric amounts of Et 3 N was found to increase the reaction rate leading to a higher reaction yield. The reaction can be easily scaled up and applied for the late‐stage functionalization of natural products and pharmaceutical compounds, including amino acids and steroid derivatives. The newly introduced functional groups include aryl, alkynyl, and boryl groups. The highly strained four‐membered ring, silacyclobutene was obtained when B 2 pin 2 was employed as the coupling partner. Mechanistic studies, including kinetic isotope effects, showed that the allenic C(sp 3 )−H bond cleavage is the rate‐limiting step.