Functionalization of Internal Arylalkynes with Nitrosylsulfuric Acid: Access to Arylated 1,2-Diketones and 1,3-Oxazoles

Nitrosylsulfuric acid was found to be an efficient oxidant for converting internal arylalkynes into their corresponding benzils. This 1,2-dicarbonylation proceeds under mild conditions at ambient temperature in nitromethane in the presence of catalytic amounts of iodine, affording benzils in 30-99% yields. Replacing nitromethane with acetonitrile crucially influences the composition of the products, with the main reaction products being substituted 1,3-oxazoles. The mechanism of the transformations was investigated by experiments with H₂¹⁸O.