Microwave-Assisted 1,3-Dioxa-[3,3]-Sigmatropic Rearrangement of Substituted Allylic Carbamates: Application to the Synthesis of Novel 1,3-Oxazine-2,4-dione Derivatives

International audienceIn a first instance, the effect of the microwave irradiation on the 1,3-Dioxa-[3,3]-sigmatropic rearrangement of aryl allylic carbamates was investigated. Under these new conditions, the reaction acceleration was clearly highlighted compared to conventional heating conditions. Depending on the electronic nature of substituents on the aromatic group, this type of rearrangement can be faster with similar or improved yields. Due to this experimental improvement, the diversity of aryl allylic carbamates able to undergo this rearrangement in a reasonable reaction time (30 min.) and with acceptable to high yields was greatly extended. Finally, an original synthetic way involving this microwave-assisted process to access new six-membered heterocyclic structures such as (E)-5-arylidene-1,3-oxazinane-2,4-diones was developed from Morita-Baylis-Hillman (MBH) adducts showing the interest of this molecular rearrangement approach. DFT and Fragment Distortion studies showed in general polar transition structures and connected high deformation and interaction energies with lower activation barriers