Stepwise Mechanism for the Bromination of Arenes by a Hypervalent Iodine Reagent
Albert Granados1, Alexandr Shafir2, Ana Arrieta3
1Departament de Química and Centro de Innovación en Química Avanzada (ORFEO-CINQA) , Universitat Autònoma de Barcelona , Cerdanyola del Vallès, 08193 Barcelona , Spain.
Abstract:
A mild, metal-free bromination method of arenes has been developed using the combination of bis(trifluoroacetoxy)iodobencene and trimethylsilyl bromide. In situ-formed dibromo(phenyl)-λ3-iodane (PhIBr2) is proposed as the reactive intermediate. This methodology using PIFA/TMSBr has been applied with success to a great number of substrates (25 examples). The treatment of mono-substituted activated arenes led to para-brominated products (2u-z) in excellent 83-96% yields. Density functional theory calculations indicate a stepwise mechanism involving a double bromine addition followed by a type II dyotropic reaction with concomitant re-aromatization of the six-membered ring.
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