Potassium Alkylpentafluorosilicates, Primary Alkyl Radical Precursors in the C-1 Alkylation of Tetrahydroisoquinolines

In this study, we demonstrate that potassium alkylpentafluorosilicates (RSiF₅K₂) are efficient primary alkyl radical precursors for selective C(sp³)-C(sp³) bond-forming reactions. RSiF₅K₂ reagents are white, free-flowing solids and are moisture and air stable. This class of reagents enables the direct C-1 alkylation of tetrahydroisoquinolines under mild conditions via single-electron transfer. The broad substrate scope of both alkylpentafluorosilicates and tetrahydroisoquinolines is tolerated in this transformation. Both radical scavenger and EPR capture experiments show that the primary radical is generated by the oxidation of RSiF₅K₂. A mechanism involving alkyl radical addition to an iminium salt followed by reduction by an amine is proposed.