Titanium-Catalyzed Reaction of Silacyclobutanes with Alkenes: Mimicking the Reactivity and Reversing the Selectivity Towards Late Transition Metals.

Transition metal-catalyzed ring opening and expansion reactions of silacyclobutanes (SCBs) constitute an atom- and step-economical strategy to construct value-added silicon-containing chemicals. Despite extensive studies, the reaction of SCBs with simple alkenes has only one precedent. Moreover, most reported reactions of SCBs use late transition metals (Pd, Ni, Rh) as catalysts. By contrast, there are no reports of using early transition metals. Herein, we report the first example, to our knowledge, of early-transition-metal-catalyzed reactions of SCBs using earth's second abundant titanium as a catalyst. Notably, orthogonal selectivity was observed. Selective activation of the relatively inert C(sp)-Si bond was achieved in the case of benzosilacyclobutenes, a selectivity that has rarely been achieved using other metals. Even for silacyclobutanes with C(sp)-Si bonds only, our titanium system also shows complementary selectivity towards late transition metals to give distinct products. Thus, structurally varied SCBs and alkenes were reacted in our system to afford structurally diverse silicon-containing products that are otherwise difficult to obtain using other transition metals.