Mechanistic photochemistry of .beta.,.gamma.-unsaturated ketones. An alternative excited state assignment for the 1,3-acyl shift reaction of alkyl .beta.,.gamma.-enones

Synthetic Aspects of the Di-π-methane Rearrangement

“…Other authors have also concurred in the involvement of the T 2 (n,π*) state in the 1,3-acyl shift. 81,82 On the other hand, a study of Koppes and Cerfontian 83 has demonstrated that ketones 37 undergo the ODPM rearrangement on direct irradiation yielding compounds 38, in a reaction thought to take place from the S 2 (π,π*) state. In another study Rogers et al 84b,c have reported that direct irradiation of ketones 39 give 40, by the ODPM rearrangement, in a reaction that was said to originate from some excited state other than the T 1 (π,π*) state.…”

The effect of wavelength on organic photoreactions in solution. Reactions from upper excited states

“…The state responsible for this reaction is suggested to be the T2 (mr*) state. 147 Doubt about S-being the reactive state in 1,3-acyl shift is cast by (i) the observation of fluorescence from both /3,7-enones which are reactive and /3,7-enones which are unreactive toward the 1,3-acyl shift; (ii) the fact that 1,3-acyl shifts are often unable to compete with intermolecular 7-hydrogen abstraction from the /3,7-enone mr*1 state; and (iii) reports that the use of the high-energy sensitizer, acetone, sometimes results in sensitized, albeit Inefficient, 1,3-acyl shift reactions of alkyl /3,7-unsaturated ketones. The quantum yield of fluorescence ( ,:) as well as the lifetime ( , ) of the /3,y ketones 101-106 were measured.…”

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

“…-I3C-NMR. '): 16,7,18,7,23,3,24,6,25,O ( 5 qa); 115,l (t, C (8) (4)); 142,l (s, C (7)). -MS.: 182 (noch sichtbar M + , C12Hz20), 139 (3), 112 @I), 110 (go), 109 (17), 97 (lo), 95 (loo), 81 (12), 73 (17), 69 (12), 67 (22) J = 7 , 3 H-C(l), H3C-C (2)); 1,20 (s, 2 H3C-C(4)); 1,80 (m, ~112'4, H3C-C (7)); 2,93 (qi, J = 7 , H-C(2)); 4,91 (s, 2H-C (8)); 5,88 vA=5,61,vB=6,15,J = 16,, H-C (6)).…”