Improved Synthesis of 1,2-Bis(trimethylsilyl)benzenes using Rieke-Magnesium or the Entrainment Method

Abstract

1,2-Bis(trimethylsilyl)benzene is the key starting material for the synthesis of efficient benzyne precursors and certain luminescent π-conjugated materials. We now report that it can be conveniently prepared in tetrahydrofuran from 1,2-dibromobenzene, chlorotrimethylsilane, and either Rieke-magnesium (Mg^R) or magnesium turnings in the presence of 1,2-dibromoethane as an entrainer (Mg^e). The most important advantages of these new protocols over the currently best-established procedure (1,2-dichlorobenzene, chlorotrimethylsilane, magnesium turnings, hexamethylphosphoramide) lie in the milder reaction conditions (Mg^R: 0 °C, 2 h; Mg^e: room temperature, 30 min vs. 100 °C, 2 days) and in the fact that the cancerogenic solvent hexamethylphosphoramide is avoided. Moreover, the improved protocols are also applicable for the high-yield synthesis of 1,2,4,5-tetrakis(trimethylsilyl)benzene, 4-fluoro-1,2-bis(trimethylsilyl)benzene, 4-chloro-1,2-bis(trimethylsilyl)benzene, and 4,5-dichloro-1,2-bis(trimethylsilyl)benzene.