Photochemistry of 9,10-dicarbonyl-9,10-dihydroanthracene - A source of 9,10-dehydroanthracene?

9,10-Didehydroanthracene (1) is an interesting derivative of p-benzyne that has been subject of several studies. In contrast to an earlier report, the photochemical decarbonylation of 9,10-dicarbonyl-9,10-dihydroanthracene (2 ) does not lead to 1 but rather to the ring-opened ene-diyne 4. The key int ermediate for this reaction is keto carbene 7 which is formed by monodecarb onylation of 2. Carbene 7 is labile towards visible-light irradiation and e asily looses the second CO molecule to give 4. Carbene 7 and diyne 4 are ch aracterized by IR and UV/Vis spectra, the IR spectra are compared to calcul ations at the B3LYP/6-31G(d,p) level of theory.