Chemistry of exciplex. 6. Quenching of the 1n,.pi.* of alkanones by unsaturated compounds

Photoaddition of olefins to cyclic imides: intermolecular oxetane formation and ring expansion

“…21 The different modes of addition between aliphatic and aromatic ones could be in part related to their possible different excited configurations. 22 This photocycloaddition described here completes the analogy between the photochemistry of simple carbonyls25 and imides.3 structure of 9a (mp 88.5-89.5 °C, 10 h, 81%13) was confirmed by comparison with an authentic specimen prepared from JV-isobutylphthalimide by photolysis and subsequent methylation.8b It is of interest that the behavior of the excited aromatic cyclic imide toward olefin is distinct from that of the aliphatic counterparts. Mazzocchi et al have recently found that JV-alkylphthalimides undergo photochemical addition of dienes whereby the diene adds with its terminal carbon attached to nitrogen, suggestive of an addition to the N-C(O)…”

“…The latter, at -78 °C, is efficiently trapped as the acetamide 3b; in the absence of an acetylating agent, as the temperature is increased from -78 °C to room temperature, 3a undergoes an unprecedented intramolecular O -* N thionacyl transfer, most probably through the intermediate T/1, to vield the more stable isomer 4a. 22 Similarly, the initially formed intermediate T2°2 1 undergoes kinetic breakdown by cleavage of the C2-N bond (in preference to C2-0) to yield 7 and 8a (Scheme II); after acetylation (-78 °C) the products are 7 and 8b. In the absence of acetylating agent at room temperature the more stable 0022-3263/79/1944-0666S01.00/0 © 1979 American Chemical Society…”

Reactions of Triplet Decafluorobenzophenone with Alkenes. A Laser Flash Photolysis Study

“…The photoreactions of excited ketones with alkenes have been the subject of numerous investigations because of the complexity of the mechanism and the synthetic utility of the reaction. − The photocycloaddition of an olefin to a ketone, the Paternò−Büchi reaction, offers a simple route to the synthesis of oxetanes. The formation of the oxetane product may be accompanied by the concomitant formation of hydrogen-atom abstraction products and cis − trans isomerization of the alkene.…”

Photochemical Synthesis of Oxetans

“…Increased alkyl substitution lowers the ionization potential of the alkene, and increases the rate of singlet exciplex formation (as can be studied from the quenching effects of the alkenes on the fluorescence of the alkanone). (27) Selectivity of attack at more substituted double bonds of alkenes is therefore likely, as evidenced by the formation of the oxetan 28 (20%) from irradiation of acetone in the presence of 3,7-dimethylocta-1,6-diene (Scheme 12). (53) In these photocycloadditions, it is possible to have some variety in the substituents on the alkene without undue detraction from the oxetan yield.…”

“…Compelling evidence for exciplex formation comes from such diverse observations as deuterium isotope effects on oxetan formation, (25) studies of the quantum yields of alkene isomerization, (26) and the temperature dependence of alkanone fluorescence quenching by alkenes. (27) Exciplex formation also allows an energy-wasting route which helps to explain the low-to-moderate quantum yields (e.g., ct> = 0.05--0.5) typically observed for oxetan production.…”