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

1,2-Bis(trimethylsilyl)benzene is the key starting material for the synthesis of efficient benzyne precursors and certain luminescent pi-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 degrees C, 2 h; Mg-e : room temperature, 30 min vs. 100 degrees C, 2 days) and in the fact that the cancerogenic solvent hexa-methylphosphoramide 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, 4chloro-1,2-bis(trimethylsilyl)benzene, and 4,5-di-chloro-1,2-bis(trimethylsilyl)benzene.