Rh(I)-Catalyzed Arylation of Heterocycles via C−H Bond Activation: Expanded Scope through Mechanistic Insight

A practical, functional group tolerant method for the Rh-catalyzed direct arylation of a variety of
pharmaceutically important azoles with aryl bromides is described. Many of the successful azole and aryl
bromide coupling partners are not compatible with methods for the direct arylation of heterocycles using
Pd(0) or Cu(I) catalysts. The readily prepared, low molecular weight ligand, Z-1-tert-butyl-2,3,6,7-tetrahydrophosphepine, which coordinates to Rh in a bidentate P-olefin fashion to provide a highly active
yet thermally stable arylation catalyst, is essential to the success of this method. By using the
tetrafluoroborate salt of the corresponding phosphonium, the reactions can be assembled outside of a
glovebox without purification of reagents or solvent. The reactions are also conducted in THF or dioxane,
which greatly simplifies product isolation relative to most other methods for direct arylation of azoles
employing high-boiling amide solvents. The reactions are performed with heating in a microwave reactor
to obtain excellent product yields in 2 h.