Tunneling control of the reactivity of noradamantylmethylcarbene – Rearrangements under cryogenic conditions

The photochemistry of noradamantyldiazoethane (28) in argon matrices at 9 K was investigated in order to experimentally corroborate computational predictions (J. Am. Chem. Soc. 2013, 135, 17274-17277) about tunneling control guiding the reactivity of noradamantylmethylcarbene (24). In line with the predictions that a rapid 1,2-H shift via hydrogen tunneling strongly limits the lifetime of 24 at T ≤ 10 K, noradamantylethene (25) was detected as the sole photoproduct. Photolysis of the trideuterated analogue CD3-28 exclusively yielded d3-25, agreeing with the prediction that deuteration severely slows down the reaction, but is insufficient to allow for the detection of CD3-24. These experimental results corroborate the predictions of rapid hydrogen tunneling dictating the reactivity of 24 under cryogenic conditions, with efforts under way to confirm the onset of ring expansion via carbon tunneling at higher temperatures.