Photochemistry of matrix-isolated 5-cyano-2H-pyran-2-one (δ-cyano-α-pyrone) and cyanocyclobuta-1,3-diene

Matrix-isolation photochemistry (λ > 299 nm; Ar, 10 K) of 5-cyano-2H-pyran-2-one (5, δ-cyano-α-pyrone) shows complete conversion to a mixture of several ring-opened ketene isomers (6) and a ring-closed Dewar lactone (7), as detected by infrared spectroscopy. Subsequent irradiation (λ > 200 nm) causes decarboxylation of the Dewar lactone (7) to produce cyanocyclobuta-1,3-diene (8). Continued irradiation (λ > 200 nm) results in the photodecomposition of cyanocyclobuta-1,3-diene (8) to cyanoacetylene and acetylene. 4-Cyanopyridine (10) was explored as an alternative photochemical precursor to cyanocyclobuta-1,3-diene (8). It was found, however, that 10 does not exhibit observable photochemistry under our irradiation conditions.