Silanes elemental halogens

The introduction of bromo substituents can convert the commercial 1,2,3-trifluorobenzene into useful building blocks (Scheme 1-2). Consecutive treatment with 5ec-butyllithium and elemental bromine gives l-bromo-2,3,4-trifluorobenzene (1, 95%). l,5-Dibromo-2,3,4-trifluorobenzene (2, 87%) forms when the silane obtained by in situ trapping of 5-bromo-2,3,4-trifluorophenyllithium with chlorotrimethylsilane is heated in the presence of elemental bromine. Upon incubation with lithium diisopropylamide, a basicity gradient-driven heavy halogen migration occurs to provide an intermediate that affords with tetrabromomethane or methanol l,2,3-tribromo-4,5,6-trifluorobenzene (3, 67%) and l,2-dibromo-3,4,5-trifluorobenzene(4,92%), respectively. 

In general, stable silylenes have been synthesized by the reduction of a dihalosilane precursor with elemental alkali metals as well as by dehydrohalogenation of respective halogenated silane precursors with a base. 

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