Synthesis of Diaryl Ethers by Formal Oxygen Insertion Between Suzuki–Miyaura Coupling Partners

Because of the broad availability of Suzuki–Miyaura cross-coupling partners (aryl (pseudo)halides and organoboron reagents), methods that can repurpose them for the divergent synthesis of many compound classes are attractive. We report a convenient three-component coupling strategy that formally inserts an oxygen atom into a Suzuki–Miyaura transformation to yield diaryl ethers. The reaction, involving in situ generation of an aryl borate intermediate by oxidation, provides a disconnection complementary to that of traditional C–O cross-coupling. The method is effective on aryl chlorides, tolerates a broad range of functional groups, and can be used when the corresponding (hetero)aryl alcohol is less accessible (unavailable, unstable, or not easily synthesized). Mechanistic studies by 1H and 11B NMR spectroscopy reveal a critical and synergistic interplay between the Pd-independent and Pd-catalyzed steps. The formation of adducts between N-methylmorpholine N-oxide (NMO) and aryl borates may hinder oxidation. On the other hand, the byproduct N-methylmorpholine accelerates ligand exchange of LPd(Ar)X with Ar′O–B(OR)2.