Microwave Induced Selective Bromination of 1,4-Quinones and Coumarins

Introduction of Halogen Atoms into Organic Compounds Under Solvent- Free Reaction Conditions

“…A continuous method was also used for bromination of toluene B1a, where ring (B2a, B3a) and side chain (B4a) brominated products were formed, while selective benzylic bromination was observed in the case of 3-nitrotoluene (B1b) [74]. The approach of introducing a bromine atom under SFRC conditions was reported with the use of molecular bromine adsorbed on neutral alumina and selective bromination of 1,4-quinones and coumarins was achieved using microwave irradiation [75].…”

Advanced Routes in Synthesis and Reactions of Lawsone Molecules (2‐Hydroxynaphthalene‐1,4‐dione)

“…The treatment of (Z)‐3‐hydroxy‐4‐(2‐(3‐methyl‐5‐oxo‐1‐phenyl‐1H‐pyrazol‐4(5H)‐ylidene)hydrazinyl)naphthalen‐1‐sulfonic acid ( 76 ) with aqueous NaOH in the presence of MnSO 4 gave 1 and 4‐diazo‐3‐methyl‐1‐phenyl‐1H‐pyrazol‐5(4H)‐one ( 76 ) (Scheme ).…”

“…Halogenation of 1 with chlorine in carbon tetrachloride (CCl 4 ) in the presence of mercury oxide , with ammonium bromide (NH 4 Br) in the presence of potassium peroxymonosulfate (oxone) or ammonium iodide (NH 4 I) in the presence of oxone yielded 2‐chloro‐3‐hydroxynaphthalen‐1,4‐dione ( 78a ), 2‐bromo‐3‐hydroxynaphthalen‐1,4‐dione ( 78b ) in yield 98% or 2‐hydroxy‐3‐iodonaphthalen‐1,4‐dione ( 78c ) in yield 81–92%, respectively (Scheme ). The suggested mechanism for compounds 78b and 78c is shown in Scheme .…”

Dioxane dibromide mediated bromination of substituted coumarins under solvent-free conditions

“…Halocoumarins also exhibit insecticidal and fungicidal properties [5]. A few methods have been documented for regioselective bromination of coumarins, which include CuBr 2 /Al 2 O 3 in bromobenzene under reflux [5], Br 2 in glacial AcOH [6], Br 2 /Al 2 O 3 under microwave irradiation [7], NBS in CHCl 3 [8], Et 4 N + Br − in the presence of hypervalent iodine reagents [9], and NBS in tetrabutylammonium bromide under molten salt conditions [10]. There is a recent report of the preparation of 3-bromocoumarins from acyclic precursors through bromination of a Wittig reagent with NBS followed by tandem Wittig reaction and cyclization [11].…”