Photochemistry of ethyl 2,3-dihydro-2,2-dimethyl-3-oxo-1H-pyrrole-1-carboxylate

The title compound 7 is obtained by reductive dehalogenation from 4-bromo-2,3-dihydro-2,2. -dimethyl-3-oxo-1H-pyrrole-1-carboxylate ( 8 ) in 90% yield, Aza-enone 7 undergoes [2 + 2] cycloaddition from the triplet state with both electron-rich and electron-deficient alkenes. The behaviour of 7 in light-induced reactions is compared to those of 2,2-dimethyl-3(2H)-furanone ( 1a ) and of the corresponding thiophenone 1b . In the photodimerization and the cycloaddition to either 2,3-dimethylbut-2-ene or to dimethyl maleate of these ketonic five-membered heterocycles with one heteroatom, the overall efficiency increases in going from the furan 1a to the thiophene 1b and to the pyrrole 7 .