A series of tertiary (fluorinated) benzenesulfonamides was synthesized in superacid HF-SbF5. To circumvent the problem of the in situ iminium ion formation, proved by low temperature NMR experiments, a tandem superacid catalysed cross-coupling reaction was employed to synthesize the benzofuzed sultams analogues. These tertiary benzenesulfonamides were tested as inhibitors of human carbonic anhydrases (hCAs, EC 4.2.1.1). These compounds did not inhibit the widespread off target hCA II isoform and showed strong selectivity toward tumor-associated carbonic anhydrase isoform IX. A dramatic effect of the electronic and structural shape of the inhibitors on selectivity was demonstrated, confirming the non-zinc-bonding mode of inhibition of this class of sulfonamides. This work allowed identifying a highly selective hCA IX inhibitor lead in this series.