Catalytic Vicinal Dichlorination of Unactivated Alkenes

Organocatalytic strategies for the programmed, catalytic oxidation of π-bonds through regioselective halogenation remain comparatively underdeveloped. The vicinal dichlorination of unactivated alkenes is a pertinent example, where stoichiometric reagents and prefunctionalization steps are often employed. This is surprising given the prominence of the 1,2-dichloro moiety in an array of bioactive natural products of both terrestrial and marine origin. Inspired by Willgerodt’s seminal discovery in 1886 that PhICl2 can be generated by passing Cl2(g) through iodobenzene, a catalytic vicinal dichlorination of unactivated alkenes has been designed on the basis of an I(I)/I(III) manifold. In situ generation of p-TolICl2 is achieved using Selectfluor and CsCl. Substrate scope, mechanistic delineation, and preliminary validation of an enantiomeric variant are established. Over a century after the initial discovery of the Willgerodt reagent (PhICl2), an operationally simple, catalytic alternative has been validated.