Photoredox mediated nickel catalyzed C(sp3)–H thiocarbonylation of ethers†
The first direct C(sp3)–H thiocarbonylation reaction is achieved by visible light photoredox/Ni dual catalysis. The thioester group of thiobenzoate is transferred to the α-oxy carbon of various cyclic/acyclic ethers, which is the opposite to the commonly expected chemical reactivity involving acyl group transfer via the weaker C(acyl)–S activation. Through mechanistic studies, we proposed that the reaction is initiated by photocatalytic reduction and fragmentation of the thioester into an acyl radical and a thiolate. A nickel complex binds to the thiolate and induces the decarbonylation of the acyl radical to form an aryl radical, which abstracts hydrogen from the α-oxy carbon of the ether. The resulting α-oxy C(sp3) centered radical re-binds to the (RS)(CO)Ni complex, which undergoes CO migratory insertion and reductive elimination to give the desired thioester product.