Photochemical reactions of cyclic, unsaturated diketones

Extensive ab Initio Study of the C2O2, C2S2, and C2OS Systems: Stabilities and Singlet−Triplet Energy Gaps

“…Since a correct description of the lowest singlet states of C 2 O 2 , C 2 S 2 , and C 2 OS needs at least a two configurational wave function, frequencies and zero-point energies were determined, for both singlet and triplet states at an MCSCF level, using the same cc-pVTZ basis set of the CI calculations. In this MCSCF treatment, a CASSCF (10,8), the 10 highest electrons were distributed in the 8 valence π-orbitals, i.e., the most important orbitals needed for a correct description of these singlet and triplet states, at their equilibrium geometries (hereafter MCSCF-(10,8)/cc-pVTZ). For comparison, the vibrational analysis has been undertaken at the same B3LYP/6-311+G(2df) level used for the geometry optimizations, and also at the B3LYP/cc-pVTZ level, to test the basis set influence on the IR spectra calculations.…”

“…No further work was recorded until 1968, but thereafter followed a series of synthetic papers, which for the most part concentrated on other matters, but either mention C 2 O 2 or describe attempts to trap it as an addendum to their main interest. [4][5][6][7][8][9][10] Around 1986, though, Birney and Berson made a deliberate attempt to find a synthetic pathway to ethylenedione. [11][12][13][14] They were unsuccessful, and all further experiments since have been unable to convincingly demonstrate that the neutral molecule exists.…”

Bond fixation in annulenes. 11. Synthesis and absolute configuration of the enantiomeric 1,3-di-tert-butylcyclooctatetraenes. Quantitative kinetic assessment of the effect of nonvicinal tert-butyl groups on [8]annulene ring-inversion and bond-shifting barriers

“…The product, which was stable for at least 1 h at room temperature, is assumed to be a mixture of the 1,2-cyclobutanedione isomers 11a and lib. 27,28 Subsequent irradiation at 536 nm caused disappearance of the 514-nm band and formation of bicyclo[4.2.0]octatriene 12. The structural assignment to 12 is in complete agreement with its spectroscopic features.…”

Photolysis of Saturated Four‐Membered Rings with Two Exocyclic Double Bonds: A Photoextrusion Route to (Hetero)Methylenecyclopropanes

“…39) in benzene, toluene, dichloromethane or deuteriochloroform as solvent, or in the solid state, the 1,2-cyclobutanediones 123 were produced as the only initial photoproducts via a 1,3-shift. 66 A mechanistic study of the photolysis of 122a indicated that the photorearrangement proceeded via a short-lived…”

“…Photolysis of the polycyclic 1,2cyclobutanediones 123 with 436 or 546 nm light or with a high pressure mercury lamp in Pyrex vessels resulted in decarbonylation and concomitant formation of the dienes 124. These were previously presumed to be generated directly from the diketones 122 66.…”