1,1,3-Trihalides synthesis with addition

Dibromomethane added dropwise with water-cooling at room temp, to a mixture of cyclohexene, Na-bis(trimethylsilyl)amide, and dry pentane, the product isolated after 2 additional hrs. at room temp. product. Y 40%. F. e. s. B. Martel and J. M. Hiriart, Synthesis 1972, 201 from 1,1,1-trihalides by irradiation in the presence of NaOH s. T. A. Marolewski and N. C. Yang, Org. Synth. 52, 132 (1972). 

A modified stepwise hydroboration avoiding the use of lithium aluminum hydride has also been developed (Schane 23.30). It was discovered that trialkylsilane reacts rapidly with boron trihalide to form unsolvated dihaloborane. Subsequent reaction with alkenes in the presence of sufficient boron trihalide occurs rapidly at -78°C to afford alkylboron dihalides without detectable contamination by dialkylboron halides. If additional equivalents of both trialkylsilane and alkene are added, dialkylboron halides are obtained. The methodology has been successfully applied to the synthesis of l,l,I-tris(dichloroboryl)alkanes, important precursors for dicarbapentaboranes. ... 

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