Copper-Catalyzed Si–B Bond Activation in the Nucleophilic Substitution of Primary Aliphatic Triflates

Abstract

A method for the nucleophilic displacement of the triflate leaving group attached to terminally functionalized alkyl groups with nucleophilic silicon is reported. Copper catalysis is used to release the silicon nucleophile from Suginome’s Si–B reagent. The functional group tolerance is excellent, and halide leaving groups do also work with the same protocol.

Key words

chemoselectivity - copper - nucleophilic substitution - silicon - transmetalation

• References and Notes

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• 18 Copper-Catalyzed Nucleophilic Substitution of Functionalized Alkyl Triflates; General Procedure A flame-dried Schlenk tube was charged with CuCN (1.1 mg, 5.0 mol%) and NaOt-Bu (36 mg, 1.5 equiv); when required, tetracosane was added as internal standard at this stage. THF was added (0.25 M), and the resulting solution was cooled to 0 °C. After 10 min, 1 (98 mg, 1.5 equiv) and the indicated triflate (0.25 mmol) were successively added. The purple solution was maintained at 0 °C or room temperature for the indicated time (monitoring by GLC analysis). The reaction was then diluted with MTBE (5 mL) and filtered through a short plug of silica gel, followed by rinsing with MTBE (2 × 5 mL). The solvents were evaporated under reduced pressure, and the crude material was purified by flash chromatography on silica gel with the indicated solvents as eluent (see the Supporting Information for details). The tetraorganosilanes were obtained as colorless oils.
• 19 The current procedure was not applicable to secondary alkyl bromides, iodides, and triflates as a result of facile elimination. High and moderate conversion was obtained for bromides and iodides, respectively, but only traces of the desired tetraorganosilanes were detected by GLC analysis; triflates were generally too labile.