Association of Fluorous “Phase‐Vanishing” Method with Visible‐Light Activation in Benzylic Bromination by Bromine

In this study the “phase‐vanishing” method for diffusion‐controlled addition of a reagent (Br 2 ) to a reaction phase via a fluorous membrane (C 8 F 18 ) is combined with an additional mode of activation (visible‐light) to achieve the benzyl bromination of various alkyl‐substituted aromatic compounds in a concentrated solution. Benzyl bromination of p ‐ tert ‐butyltoluene proceeded in various solvents including hexane and methanol, while the reaction of the neat substrate showed a similar selectivity as in carbon tetrachloride. The effect of the substituent on the para position of toluene on the course of bromination revealed three processes: benzyl bromination with H, Me, t Bu and CO 2 Et substituents, aromatic bromination with OMe and NHAc substituents and the reaction of the 4‐acetyl derivative at the substituent to form an α‐bromo ketone.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)