Aromatic halogenation reactions are among the oldest known organic reactions.Multiple kinetic and mechanistic studies have been reported as well as extensive studies on the catalysis of these reactions. In general it is well recognized that monosubstituted phenyl rings, where the substituent is electron donating, usually halogenate at either the ortho or para positions. Likewise when the substituent is electron-withdrawing, substitution occurs preferentially in the meta position. These results have long been explained as an effect of conjugation in the transition state that stabilizes the cationic intermediate in the case of electron donating substituents and does exactly the opposite for electron accepting substituents. Although halogenations usually require the use of catalysts to promote electrophilic substitution there are examples where no catalysts are needed to effect efficient and multiple halogenation as seen in reactions of phenols or anilines. In contrast, efforts to halogenate aromatic rings with highly electron withdrawing groups such as nitro or CF3- require the use of catalysts such as FeX3 and relatively high temperatures.We report here direct orthobromination of aromatic rings without catalysts and with highly electron withdrawing groups. Figure 1.   The relative stabilities of Br substitution at ortho, para or meta sites were also calculated in order to study the bromination mechanism of T8 cage.

Highly selective, autocatalytic ortho bromination of [PhSiO<sub>1.5</sub>]<sub>8,10,12</sub> via a venus flytrap mechanism

248th National Meeting (2014)

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Highly selective, autocatalytic ortho bromination of [PhSiO1.5]8,10,12 via a venus flytrap mechanism

Highly selective, autocatalytic ortho bromination of [PhSiO_1.5]_8,10,12 via a venus flytrap mechanism