A Radical Cascade with Double Intramolecular Hydrogen Atom Transfer for the Generation of Bisfunctionalized Cyclopentanes from Linear Alkynes

Radical cascade reactions represent a powerful synthetic tool for the preparation of complex molecules from easily assembled starting materials. The incorporation of an intramolecular hydrogen atom transfer step in the cascade enhances considerably the level of complexity that can be achieved in a single synthetic operation. We describe here an efficient radical cascade process that involves the activation of two aliphatic C-H bonds in a series of five elementary steps. It converts efficiently readily available terminal alkynes into functionalized cyclopentylmethyl arylsulfones, which are highly valuable and flexible synthetic intermediates, as demonstrated by the preparation of diquinanes and triquinanes possessing a rare trans ring junction. This work illustrates also the unique reactivity of α-sulfonylated alkyl radicals in C-H bond activation processes.