Light‐induced Dehydrodimerization of 3‐Hydroxypyrroles

Irradiation (λ > 280 nm) of 3‐hydroxy‐1 H ‐pyrrole‐2‐carboxylates 1 in CH 3 CN gives the [2.2′‐bi(3‐oxo‐2,3‐dihydro‐1 H ‐pyrrole)]‐2‐,2′‐dicarboxylates 2 in reasonable to good yields. The corresponding N ‐methylpyrroles 3 only undergo slow photodecomposition under similar conditions. Several 2‐methyl‐3‐oxo‐2,3‐dihydro‐1 H ‐pyrrole‐2‐carboxylates 4 and 5 were synthesized to compare their spectral data with those of the dehydrodimers 2 . A X‐ray structure analysis was performed for diethyl [2,2′‐bi(4,5‐dimethyl‐3‐oxo‐2,3‐dihydro‐1 H ‐pyrrole)]‐2,2′‐dicarboxylate ( 2b ). The originally proposed [3,3′‐bi(3 H ‐pyroole)] structure for compounds 2a ‐ e proves incorrect.