Synthesis of bromo-, boryl-, and stannyl-functionalized 1,2-bis(trimethylsilyl)benzenes via Diels-Alder or C-H activation reactions

Article abstract of DOI:10.1021/jo3002936

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.