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.