Benzylic C(sp3-H) functionalisation of electron-poor substrate with photoexcited DDQ

2,3-Dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) is a common oxidant familiar to many organic chemists as it employed for myriad oxidation reactions, including the functionalisation of electron-rich benzylic C(sp3)–H bonds. Under photochemical excitation, DDQ becomes a very powerful oxidant, but has scarcely been utilised for C(sp3)–H functionalisation. Here, we report that the photochemical excitation of DDQ can be used as a strategy for the functionalisation of electron-poor benzylic C(sp3)–H bonds. The product is a benzylic hydroquinone ether – a known synthetic linchpin. The methodology is amenable to both batch and flow setups and is demonstrated on a series of primary and secondary benzylic substrates. Transient absorption spectroscopy has revealed mechanistic insight into the electron transfer processes involved, indicating a single electron transfer pathway operates under these photochemical conditions, which contrasts with a hydride mechanism previously reported to occur when employing ground-state DDQ.