ISSN:
1434-193X
Keywords:
Singlet oxygen
;
Photooxygenation
;
Cycloaddition
;
Ene reactions
;
Kinetics
;
Phosphorescence quenching
;
Chemistry
;
General Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
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 ko ( = kr + kq) was additionally measured in chloroform solutions by singlet-oxygen (1Δg) 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.
Additional Material:
4 Ill.
Type of Medium:
Electronic Resource
