Dimethyldioxirane Converts Benzene Oxide/Oxepin into (Z,Z)-Muconaldehyde and sym-Oxepin Oxide: Modeling the Metabolism of Benzene and Its Photooxidative Degradation

Oxidation of 7-oxabicyclo[4.1.0]hepta-2,4-diene (benzene oxide)/oxepin with dimethyldioxirane (DMDO) gave mainly (Z,Z)-muconaldehyde, with complete diastereoselectivity. Similarly, 2-methyl-7-oxabicyclo[4.1.0]hepta-2,4-diene (toluene 1,2-epoxide)/2-methyloxepin gave (Z,Z)-1,6-dioxohepta-2,4-diene, while 2,6-dimethyl-7-oxabicyclo[4.1.0]hepta-2,4-diene (1,2-dimethylbenzene 1,2-epoxide)/2,7-dimethyloxepin gave (Z,Z)-2,7-dioxo-3,5-octadiene. By monitoring the DMDO oxidation of benzene oxide/oxepin by 1H NMR spectroscopy, a significant byproduct was identified as 4,8-dioxabicyclo[5.1.0]octa-2,5-diene (sym-oxepin oxide). This observation supports the hypothesis that the route to (Z,Z)-muconaldehyde proceeds from oxepin via 6,8-dioxabicyclo[5.1.0]octa-2,4-diene (oxepin 2,3-oxide), with a minor pathway leading to sym-oxepin oxide. The DMDO oxidations described provide model systems for the cytochrome P450-dependent metabolism of benzene and for the atmospheric photooxidation of benzenoid hydrocarbons.