Rhodium-Catalyzed Carbon-Silicon Bond Activation for Synthesis of Benzosilole Derivatives

A rhodium-catalyzed coupling reaction of 2-trimethylsilylphenylboronic acid with internal alkynes is developed for the synthesis of 2,3-disubstituted benzosilole derivatives. A range of functional groups, encompassing ketones, esters, amines, aryl bromides, and heteroarenes, are compatible, which provides rapid access to diverse benzosiloles. Sequential 2-fold coupling enables modular synthesis of asymmetrically substituted 1,5-dihydro-1,5-disila-s-indacene, a pi-extended molecule of interest in organic electronics. In terms of the mechanism, the reaction involves cleavage of a C(alkyl)-Si bond in a trialkylsilyl group, which normally requires extremely harsh conditions for activation. Mechanistic studies, including effects of substituents, reveal C-Si that bond cleavage does not proceed through a hypercoordinated silicon species, but rather through a rhodium-mediated-activation process. The potential use of the reaction in catalytic asymmetric synthesis of Si-chiral benzosiloles is also, demonstrated.