Metal-free synthesis of ortho-CHO diaryl ethers by a three-component sequential coupling.

A practical, metal-free, and highly chemoselective approach was developed for the synthesis of ortho-CHO diaryl ethers by a three-component sequential coupling of arynes, N,N-dimethylformamide (DMF), and diaryliodonium salts. Diverse functional groups including halo, nitryl, and bulky substituents and heteroaromatics are well tolerated. Mechanistically, isotopic tracer experiments reveal that the diaryliodonium salt serves as an electrophile to trap the transient intermediates generated from the [2 + 2] cyclization of an aryne and DMF.