Photooxygenation of 2, 4-Dimethyl-1, 3-pentadiene: Solvent Dependence of the Chemical (Ene Reaction and [4 + 2]Cycloaddition) and Physical Quenching of Singlet Oxygen
Germany;
Institut fur Physikalische Chemie der Universitat zu Koln;
Greinstrasse 4;
D-50939 Koln;
Institut fur Organische Chemie der Universitat zu Koln;
Luxemburger Strasse 116;
关键词：
cycloaddition;
singlet oxygen;
photooxygenation;
ene reactions;
kinetics;
phosphorescence quenching;
期刊名称：
European journal of organic chemistry
i s s n：
1434-193X
年卷期：
1998 年
0 卷
12 期
页 码：
2833-2838
页 码：
摘 要：
The photooxygenation of 2, 4-dimethyl-1, 3-pentadiene (1) was investigated in seven polar and nonpolar solvents by oxygen-uptake measurements. The overall deactivation rate k_o(= k_r + k_q) was additionally measured in chloroform solutions by singlet-oxygen (~1Δ_G) phosphorescence quenching which showed excellent agreement with the data from the detailed steady-state kinetics. The difference in solvent-polarity effects on the [4 + 2] cycloaddition (major path, leading to the endoperoxide 2) and ene reaction (minor path, leading to the allylic hydroperoxide 3) are explained by competition between a concerted and a perepoxide mechanism. In all solvents the physical quenching of singlet oxygen by 1 is at least as efficient as the chemical quenching. The reaction of the endoperoxide 2 and 3, 3, 6, 6-tetramethyl-1, 2-dioxene 9 with carbonyl compounds in the presence of TMSOTf resulting in the dihydrofuran 8 and the 1, 2, 4-trioxane 10, was also studied.
分享
载入中，请稍后...
