Iron-Catalyzed Synthesis of 1,1-Disubstituted Allenylic Silyl Ethers Through Regioselective C(sp2)−H Functionalization of Allenes

We report a synthesis of allenylic silyl ethers through iron-catalyzed functionalization of the C(sp2)−H bonds of monosubstituted alkylallenes. In the presence of a cyclopentadienyliron dicarbonyl based catalyst and triisopropylsilyl triflate as a silylation agent, a variety of aryl aldehydes were suitable coupling partners in this transformation, furnishing a collection of 1,1-disubstituted allenylic triisopropylsilyl ethers as products in moderate to excellent yields as a single regioisomer. Lithium bistriflimide was identified as a critical additive in this transformation. The optimized protocol was scalable, and the products were amenable to further transformation to give a number of unsaturated, polyfunctional derivatives.