Versatile Tetrasilane for Time-Controlled Palladium-Catalyzed Divergent Synthesis of Silacycles via C-H Activation.

Transition-metal-catalyzed intermolecular annulation of silicon reagents with organic molecules is still underdeveloped due to the scarcity of silicon reagent types and their diverse reactivity. Herein, a readily accessible silicon reagent (octamethyl-1,4-dioxacyclohexasilane) has been developed for divergent synthesis of silacycles via time-controlled palladium-catalyzed cascade C-H silacyclization. This protocol enables the rapid and selective transformation of acrylamides into spirosilacycles with different ring sizes, including benzodioxatetrasilecines, benzooxadisilepines, and benzosiloles, in moderate to good yields through a time switch. Notably, the tetrasilane reagent can also be utilized for C-H silacyclization of 2-halo- N -methacryloylbenzamides and 2-iodobiphenyls, leading to diverse fused silacycles. Furthermore, several synthetic transformations of products are achieved. A series of mechanistic studies demonstrate the transformation relationships and possible pathways among ten-, seven-, and five-membered silacycles.