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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
Author(s) -
Griesbeck Axel G.,
Fiege Maren,
Gudipati Murthy S.,
Wagner Robert
Publication year - 1998
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/(sici)1099-0690(199812)1998:12<2833::aid-ejoc2833>3.0.co;2-6
Subject(s) - chemistry , photooxygenation , singlet oxygen , photochemistry , quenching (fluorescence) , ene reaction , cycloaddition , solvent , solvent effects , chloroform , allylic rearrangement , oxygen , phosphorescence , organic chemistry , catalysis , fluorescence , physics , quantum mechanics
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 ( 1 Δ 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.