Direct C-H Carboxylation Forming Polyfunctionalized Aromatic Carboxylic Acids by Combined Brønsted Bases.

CO fixation into electron-deficient aromatic C-H bonds proceeds with the combined Brønsted bases LiO--Bu and LiO--Am/CsF/18-crown-6 (-Am = CEtMe) under a CO atmosphere to afford a variety of polyfunctionalized aromatic carboxylic acids.

Direct Carboxylation of Electron-Rich Heteroarenes Promoted by LiO-tBu with CsF and [18]Crown-6.

We herein demonstrate that the combination of LiO-tBu, CsF, and [18]crown-6 efficiently promotes the direct C-H carboxylation of electron-rich heteroarenes (benzothiophene, thiophene, benzofuran, and furan derivatives). A variety of functional groups, including methyl, methoxy, halo, cyano, amide, and keto moieties, are compatible with this system. The reaction proceeds via the formation of a tert-butyl carbonate species.