Oxidative functionalization of adamantane and some of its derivatives in solution

1,2,4,5-Benzenetetracarbonitrile (TCB) is irradiated in the presence of adamantane (1) and some of its derivatives. The singlet excited state of TCB is a strong oxidant, and there is various evidence, including time-resolved spectroscopy, to prove that SET from the alkane to TCB1* takes place and yields the corresponding radical ions. The adamantane radical cation deprotonates from the bridgehead position, and the resulting radical couples with TCB-.. Deprotonation via the radical cation occurs with a number of substituted adamantanes and remains the exclusive or predominating reaction also with derivatives containing a potential electrofugal group, such as one of the following carbocations: t-Bu, CH(2)OMe, CH2OH (notable here is that C-H deprotonation is more efficient than O-H deprotonation). A carboxy group is lost more efficiently than a proton, however. In contrast, detaching of such cations is the main process when the radical cations of substituted adamantanes is produced anodically. This different behavior is explained on the basis of thermochemical calculation and of the different environments experienced by the radical cation in the two cases, viz reaction from the solvated radical cation in the first case and from the substrate adsorbed on the anode in the latter one. 1-Methoxyadamantane deprotonates from the methyl group, a reaction explained by the different structure of the radical cation. On the other hand, the radical NO3., conveniently produced by photolysis of cerium(IV) ammonium nitrate, reacts by hydrogen abstraction with selective attack at the bridgehead position and little interference by substituents and thus offers a useful way for the selective oxidative functionalization of adamantanes.