%0 Journal Article
%T Substrate Directed Regioselective Monobromination of Aralkyl Ketones Using N-Bromosuccinimide Catalysed by Active Aluminium Oxide: ¦Á-Bromination versus Ring Bromination
%A Reddy Bodireddy Mohan
%A G. Trivikram Reddy
%A N. C. Gangi Reddy
%J ISRN Organic Chemistry
%D 2014
%R 10.1155/2014/751298
%X Bromination of aralkyl ketones using N-bromosuccinimide in presence of active Al2O3 provided either ¦Á-monobrominated products in methanol at reflux or mononuclear brominated products in acetonitrile at reflux temperature with excellent isolated yields depending on the nature of substrate employed. The ¦Á-bromination was an exclusive process when aralkyl ketones containing moderate activating/deactivating groups were subjected to bromination under acidic Al2O3 conditions in methanol at reflux while nuclear functionalization was predominant when aralkyl ketones containing high activating groups were utilized for bromination in presence of neutral Al2O3 conditions in acetonitrile at reflux temperature. In addition, easy isolation of products, use of inexpensive catalyst, short reaction time (10¨C20£¿min), and safe operational practice are the major benefits in the present protocol. 1. Introduction Nowadays, researchers are focusing on the development of more acceptable bromination protocols to accomplish increasing demands for ¡°organohalogen¡± chemistry and to achieve higher efficiency and selectivity of the bromination reactions which include ¦Á-bromination and nuclear bromination. The resulting ¦Á-brominated or nuclear brominated products acquired wide range of utility in organic synthesis [1¨C3]. Nuclear brominated ketones are found to be useful intermediates in C¨CC coupling reactions, as precursors to organometallic species and in nucleophilic substitutions. It is well known that use of molecular bromine [4] as a basic electrophilic brominating reagent has several drawbacks. Alternative reagents were reported in the literature, for example, cupric bromide [5], dioxane dibromide [6], tetrabutyl ammonium tribromide [7], H2O2-HBr [8], bromodimethyl sulfoniumbromide [9], ethylene bis(N-methyl imidazolium) ditribromide [10], trihaloisocyanuric acids [11], pyridinium bromochromate [12], and NH4Br-oxone [13]. In addition, a popular and superior brominating agent such as N-bromosuccinimide [14] was utilized for ¦Á-bromination of carbonyl compounds using a radical initiator such as azobisisobutyronitrile (AIBN) or dibenzoyl peroxide (BPO) [15] and, later, it has been demonstrated that the reactivity of NBS could be modulated with ionic liquids [16], photochemical energy [17]; sonochemical energy [18], solvent free reaction conditions (SFRC) [19] and various catalysts such as Mg(ClO4)2 [20], NH4OAc [21], amberlyst-15 [22], silica supported NaHCO3 [23], sulfonic acid functionalized silica [24], FeCl3 [25], montmorillonite-K10 [26], and Silica gel [27]. NBS also is
%U http://www.hindawi.com/journals/isrn.organic.chemistry/2014/751298/