Photochemical, photophysical, and theoretical studies of 3,5-cycloheptadienones

Photochemische Reaktionen. 109. Mitteilung [1]. Zur Photochemie konjugierter δ‐Keto‐enone und β,γ,δ,ϵ‐ungesättigter Ketone

“…-l3C-NMR.I): 20,0, 23,3 (4qa, je 2qa iiberlagert, 2 H3C-C(5), H3C-C (7), C(8)); 27,2 (qa, C(1)); 35,4 (d, C (7)); 129, 6, 149,7 (2d. C(3), C(4)); 69 (12), 43 (100), 41 (22). 51,O (s, C (5)); 197,2 (s, C (2)); 214,4 (s, C (6)).…”

“…-I3C-NMR. '): 19,7,19,9,22,2,23,O (4 qu,4 CH3); 41,4 (I, C (5) (4) S, 3080m, 2970s, 29303, 2915s, 2875m, 2860m S, 1710s. 1665m, 1640m, 1465s, 1445s, 1385s, 1375s, 1365m S, 1350m, 1295m, 1173~1, 1125m, 1090m, 1035~1, 1015m 2870s.…”

The Photochemistry of 5,6‐Dimethylidene‐2‐norborananone. Synthesis and Diels‐Alder Reactivity of 2,3‐Dimethylidenebicyclo‐[2.1.1]hexane

“…Cyclohepta-3,5-dienones are known to undergo a-cleavage under ,Ilrr> 300 nm, probably via a S , (n, z*)-state [6]. In 3, the S1 (n, z*)-and TI (n, z*)-states do not lead to any observable decarbonylation.…”

“…and (3) the bichromophoric reactions (1,2-and 1,3-acyl shifts, intramolecular oxetane formation, etc.). The photoreactions of a, y , 6, e-unsaturated ketones in which the carbonyl function looks at the 'front' of the diene, as depicted in 1, have been illustrated abundantly [2] [6]. The photochemistry of bichromophoric systems [7] in which an homoconjugated carbonyl group looks at the 'back' of a diene, as depicted in 2, has received little attention3).…”

“…Photolysis of 5,6-dimethylidene-2-norbornanone. -Contrary to 2,3-dimethylidene-7-norbornanone [8] and to other p, y -and p, y , 6 , &-unsaturated ketones [2] [6], the keto-diene 3 is little photoreactive. Under direct irradiation at A> 300 nm (Pyrex, high-pressure Hg lamp, -50 to + 30") only slow polymerization of 3 was observed (quantum yield < 0.02) in pentane, acetone or methanol.…”