CYCLIC PEROXIDE .80. 1,4-DIMETHYL-2,3,7-TRIOXABICYCLO[2.2.1]HEPT-5-ENE - SYNTHESIS AND CHARACTERIZATION

The use of 2, 5-dimethylfuran (1) as a diagnostic test for singlet oxygen in chemical and especially biological systems is amply documented.3 For example, the formation of 2, 5-dimethyl-2-hydroperoxy-5-hydroxydihydrofuran (3a) from 1 in the acetaldehyde-xanthine oxidase system was construed as evidence that the endoperoxide 2 intervened as the enzymatic singlet oxygenation product of 1 (eq l).4 In fact, for mation of 3b in the photosensitized oxygenation of 1 with methanol as solvent5 lent credence to this supposition. Indeed, gas-phase singlet oxygenation of 1 and condensing the product stream onto a liquid nitrogen cold finger gave the monomeric endoperoxide 2; but on warming above-30 °C it quickly polymerized with oxygen evolution.6 We now provide evidence that the monomeric endoperoxide 2 can be formed quantitatively on photosensitized singlet oxygenation of 1 in CCI4 or CFCIi at 0-5 °C, and contrary to previous reports5, 6 it is remarkably stable in solution even at room temperature (ca. 25-30 °C). Our evidence includes the following: (1) a 99.3% peroxide titer (iodometry) based on 2; (2) low temperature bulb-to-bulb codistillation with CCI4; (3) conversion into the hydroperoxide 3b on treatment with methanol; and (4) quantitative deoxygenation into 1, 2-diacetylethylene with triphenylphosphine. The experimental details are described below. © 1979, American Chemical Society. All rights reserved.