ModifiedB‐Alkylcatecholboranes as Radical Precursors

Abstract Generation of radicals from B ‐alkylcatecholboranes represents an efficient tin‐free procedure for the generation of alkyl radicals. A modified version of this method has been developed. The simple catechol is replaced by a dihydroxylated tetrahydroisoquinoline, which can be separated from the reaction products by simple extraction with an aqueous acid solution. The modified alkyl radical precursors are easily prepared from alkenes by hydroboration with BH 3 · Me 2 S followed by treatment with the dihydroxytetrahydroisoquinoline. The new alkylboronates of this type are suitable radical precursors in a wide range of reactions such as sulfenylation, allylation, alkynylation, vinylation, and addition to quinones. This strategy is particularly useful when separation of reaction products from catechol residues is problematic, as illustrated by a radical addition to 1,4‐benzoquinone leading to 2‐alkyl‐1,4‐hydroquinones.