The stereoselectivity of addition of benzoyloxyl radicals to trans-Δ2-octalin

Abstract

The stereochemistry of addition of benzoyloxyl radicals to the conformationally rigid cyclohexene, trans-Δ²-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 (axial∶equatorial = 1.7∶1.0). The aminoxyl trapping reaction was more selective with a ratio of trans∶cis addition of 4.4∶1.0. Interestingly, when the benzoate group is axial, axial trapping by the sterically hindered aminoxyl is strongly favoured (axial∶equatorial = 7.4∶1.0), whereas when the benzoate group is equatorial, there is only a small preference for equatorial trapping by the aminoxyl (equatorial∶axial = 2.4∶1.0). 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.