A Novel Synthesis of 1,3-Oxazine-2,4-diones via a Simple and Efficient Reaction of CO₂ with 2,3-Allenamides

A simple and efficient reaction of CO2 with 2,3-allenamides under mild conditions (CO2 balloon without any metal catalyst in the presence of K2CO3 or Cs2CO3) leads to an efficient synthesis of 1,3-oxazine-2,4-diones. The high reactivity of the allene moiety is crucial for the success of this transformation since the corresponding reaction of α,β-unsaturated alkenamides or alkynamides does not occur.