Synthesis of Bromo-, Boryl-, and Stannyl-Functionalized 1,2-Bis(trimethylsilyl)benzenes via Diels–Alder or C–H Activation Reactions

1,2-Bis­(trimethylsilyl)­benzenes are key starting materials for the synthesis of benzyne precursors, Lewis acid catalysts, and certain luminophores. We have developed efficient, high-yield routes to functionalized 4-R-1,2-bis­(trimethylsilyl)­benzenes, starting from either 1,2-bis­(trimethylsilyl)­acetylene/5-bromopyran-2-one (2) or 1,2-bis­(trimethylsilyl)­benzene (1)/bis­(pinacolato)­diborane. In the first reaction, 5 (R = Br) is obtained through a cobalt-catalyzed Diels–Alder cycloaddition. The second reaction proceeds via iridium-mediated C–H activation and provides 8 (R = Bpin). Besides its use as a Suzuki reagent, compound 8 can be converted into 5 with CuBr2 in i-PrOH/MeOH/H2O. Lithium–bromine exchange on 5, followed by the addition of Me3SnCl, gives 10 (R = SnMe3), which we have applied for Stille coupling reactions. A Pd-catalyzed C–C coupling reaction between 5 and 8 leads to the corresponding tetrasilylbiphenyl derivative. The bromo derivative 5 cleanly undergoes Suzuki reactions with electron-rich as well as electron-poor phenylboronic acids.