Difunctionalisation of Arenes and Heteroarenes by Directed Metallation and Sulfoxide–Magnesium Exchange

The aryl sulfoxide moiety allows an expedient two-step difunctionalisation of readily available diaryl sulfoxides. Highly functionalised 1,2,4-trisubstituted arenes and difunctionalised heteroarenes (furans, thiophenes, benzofurans and pyridines) were prepared in a two-step sequence, triggered by an aryl sulfoxide group. In the first step, the sulfoxide moiety acts as a metallation-directing group, allowing smooth ortho-magnesiation with TMPMgCl⋅LiCl (TMP=tetramethylpiperidine). After a quenching reaction with an electrophile, the resulting sulfoxide is converted into a second magnesium reagent with iPrMgCl⋅LiCl (sulfoxide–magnesium exchange), which can be trapped with various electrophiles. Highly chemoselective TMPMgCl⋅LiCl and iPrMgCl⋅LiCl are compatible with a broad range of functional groups (e.g., F, Cl, CF3, CN, CO2tBu, alkynyl, ethers, thioethers). Large-scale reactions (25–40 mmol) and the preparation of fully functionalised furans and thiophenes are also reported.