Photoinduced Borylation of the Inert C(sp3)–O Bond of Alkyl Heteroaryl Ethers

A photoinduced reductive C_alkyl-O borylation of alkyl heteroaryl ethers with very negative reduction potential in the presence of 4-dimethylaminopyridine (DMAP) and bis(catecholato)diborane(B₂cat₂) was developed. Despite the high reducing power, various substrates with liable functional groups were well-tolerated as well as ethers derived from natural products and medicinal-relevant compounds. Mechanistic investigation implied that an intra-single electron transfer process in an electron donor-acceptor complex formed from ethers with the adduct of B₂cat₂ and DMAP should be involved.