Photooxygenation of 5-Dialkylamino-4-pyrrolin-3-ones. Synthesis of Highly Functionalized Ureas, 2-Oxazolidinones, and 2-Oxazolinones

5-Dialkylamino-4-pyrrolin-3-ones, available from cyclocondensation of amidines with dimethyl acetylenedicarboxylate (DMAD), undergo rapid singlet oxygenation to give highly functionalized ureas by way of a 1,2-dioxetane cleavage of the initially formed [2 + 2] cycloadducts. These latter compounds undergo cyclization to 2-oxazolidinones in MeOH. Catalytic hydrogenation of the ureas in EtOAc gives 2-oxazolinones. The DBU-DMAD adduct undergoes photooxygenation by an entirely different pathway to give a large ring heterocycle.