The stereoselectivity of addition of benzoyloxyl radicals to trans-A2-octalin

Abstract

The stereochemistry of addition of benzoyloxyl radicals to the conformationally rigid cyclohexene, trans-2-octalin, in the presence of the free radical scavenger 1,1,3,3-tetramethyl-2,3-dihydro-1H-isoindol-2-yloxyl, is reported. Axial addition was favoured over equatorial addition with modest selectivity (axialequatorial = 1.71.0). The aminoxyl trapping reaction was more selective with a ratio of transcis addition of 4.41.0. Interestingly, when the benzoate group is axial, axial trapping by the sterically hindered aminoxyl is strongly favoured (axialequatorial = 7.41.0), whereas when the benzoate group is equatorial, there is only a small preference for equatorial trapping by the aminoxyl (equatorialaxial = 2.41.0). The structures of the four possible addition products were determined by 1H and 13C NMR spectroscopy, and confirmed in the case of the diaxial addition product [2(ax)-benzoyloxy-3(ax)-(1,1,3,3-tetramethyl-2,3-dihydroisoindol-2-yloxy)-trans-decalin 3] by X-ray crystallographic analysis.