Synthesis of 1,3-oxazine-2,4-diones by DBU-catalyzed incorporation of carbon dioxide into 3-ynamides

Abstract A new process for the utilization of carbon dioxide to give high value added 1,3-oxazine-2,4-diones is presented. It is based on the catalytic carboxylative heterocyclization of readily available 3-ynamides, using 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) as organocatalyst. The reaction, which takes place under relatively mild conditions [80 °C for 15 h in a 3:1 mixture (v/v) of MeCN-HC(OMe)3, under 30 atm of CO2] proceeds through an ordered sequence of steps, involving substrate deprotonation by DBU, nucleophilic attack to CO2, 6-exo-dig cyclization, and isomerization, to give the final products in 44–85 % yields over 16 examples.