The mechanism of solvolysis of 2-adamantyl azoxytosylate: isotopic labelling, medium effect, and attempted deoxygenation studies

Rates of solvolysis of 2-adamantyl azoxytosylate (1) have been measured over a range of temperatures in ethanoic acid, methanoic acid, 50:50 (v/v) trifluoroethanol:water, 80:20 (v/v) trifluoroethanol:water, 97:3 (w/w) trifluoroethanol:water, and 70:30 (v/v) ethanol:water. For comparison, rates of solvolysis of 2-adamantyl tosylate (2) have also been measured in 50:50, 80:20, and 90:10 (v/v) trifluoroethanol:water, and for both compounds, activation parameters have been determined. These and results published earlier allow a correlation of the two reactions and indicate that the in value for 2-adamantyl azoxytosylate solvolysis is only 0.46. This is one of the lowest in values for a reaction that is unambiguously an S(N)1 solvolysis. We have also recorded the O-17 NMR spectrum of the 2-adamantyl tosylate formed from O-17-labelled 2-adamantyl azoxytosylate in deuteriochloroform, and the millimeter-wave spectrum of the nitrous oxide evolved in the hydrolysis of O-18-labelled 2-adamantyl azoxytosylate. These labelling studies have provided more detailed knowledge of the SN1 fragmentation mechanism of I and exclude a mechanism of reaction via rearrangement to N-nitroso,N-(2-adamantyl),O-(p-toluenesulfonyl)hydroxylamine (5). Attempted deoxygenation of 1 to give 2-adamantyl diazotosylate (8) and a subsequent fragmentation proved unsuccessful.