Iridium-Catalyzed Arene Ortho-Silylation by Formal Hydroxyl-Directed C−H Activation

A strategy for the ortho-silylation of aryl ketone, benzaldehyde, and benzyl alcohol derivatives has been developed in which a hydroxyl group formally serves as the directing element for Ir-catalyzed arene C−H bond activation. One-pot generation of a (hydrido)silyl ether from the carbonyl compound or alcohol is followed by dehydrogenative cyclization at 80−100 °C in the presence of norbornene as a hydrogen acceptor and the combination of 1 mol % [Ir(cod)OMe]₂ and 1,10-phenanthroline as a catalyst to form benzoxasiloles. The synthetic utility of the benzoxasilole products is demonstrated by conversion to phenol or biaryl derivatives by Tamao−Fleming oxidation or Hiyama cross-coupling. Both of these transformations of the C−H silylation products exploit the Si−O bond in the system and proceed by activation of the silyl moiety with hydroxide, rather than fluoride.