The photochemical approach to the functionalization of open-chain and cyclic alkanes: 1. Single electron transfer oxidation

Abstract

Irradiation of 1,2,4,5-benzenetetracarbonitrile (TCB) in the presence of various open-chain, cyclic and polycyclic alkanes leads to single electron transfer (SET), k et 10 8 to 10 10 M −1s −1, as demonstrated by the detection of the TCB radical anion. This affords a way to evaluate the oxidation potential of such substrates, which are difficult to measure voltammetrically. The thus formed alkane radical cations undergo deprotonation, in accordandance with thermochemical predictions showing that these species are strong acids (pK a < −13). The alkyl radical is trapped by TCB −· to yield alkylbenzenetricarbonitriles. Deprotonation occurs from the contact ion pair. With open-chain derivatives, it takes place selectively from the more substituted position, while with cyclic and policyclic alkanes the position of deprotonation depends on the radical ion pair structure.