Vanadium (V) oxide mediated bromolactonization of alkenoic acids

Abstract A full account of our recently communicated method for the V 2 O 5 mediated bromolactonization of alkenoic acids is presented. Here we describe the extensive evaluation of the metal oxide catalyst, terminal oxidant, halide source, solvent system, and reaction temperature that resulted in optimal conditions employing 0.05 equiv V 2 O 5 , 3 equiv urea-hydrogen peroxide complex (UHP), and 3 equiv of NH 4 Br in an acetone:H 2 O (6:1) solvent system at room temperature. Additionally, we have expanded the substrate scope of the reaction with the aim of evaluating the functional group tolerance of the transformation. Further, we present preliminary data of a related halogenation of β-diketones with our optimal conditions. Finally, we probed the role of urea in the transformation.