Oxidative Dimerization of Silylallenes via Activation of the Allenic C(<i>sp</i>²)–H Bond Catalyzed by Copper(I) Chloride and <i>N</i>‑Hydroxyphthalimide

Novel oxidative dimerization of silylallenes is described. Treatment of silylallenes with a catalytic amount of copper­(I) chloride, a substoichiometric amount of N-hydroxyphthalamide, and a stoichiometric amount of a terminal oxidant diacetoxyiodobenzene afforded head-to-head dimers as the main products. Silyallenes containing a small ring afforded only dimers, whereas as the ring size increased 1,3-enynes became more favorable products. For silylallenes containing an acyclic substituent, dimer formation is a norm with exceptions where N-hydroxyphthalimide reacts at the propargylic center to generate the corresponding aminoxy ethers.