Synthesis of fluorinated carbazoles via C-H arylation catalyzed by Pd/Cu bimetal system and their antibacterial activities.

An effective intramolecular C-H arylation reaction catalyzed by a bimetallic catalytic system Pd(OAc)2/CuI for the synthesis of fluorine-substituted carbazoles from corresponding N-phenyl-2-haloaniline derivatives under ligand free conditions is demonstrated. The established method is effective for both N-phenyl-2-bromoaniline and N-phenyl-2-chloroaniline, and requires the low loading of Pd(OAc)2 (0.5 mol%). A series of new fluorinated carbazoles were synthesized in excellent yields using the protocol (>83%, 19 examples) and were fully characterized by (1)H, (13)C and (19)F NMR spectral data, HRMS and elemental analysis. All compounds were evaluated for their antibacterial activities against four bacteria (Bacillus subtilis, Staphylococcus aureus, Escherichia coli and methicillin-resistant S. aureus with resistance to gentamicin) by serial dilution technique. All tested compounds showed antibacterial activity against three test strains (S. aureus, B. subtilis and MRSA), and most of these compounds displayed pronounced antimicrobial activities against these three strains with low MIC values ranging from 0.39 to 6.25 µg/mL. Among them, compounds 7 and 14 exhibited potent inhibitory activity better than reference drugs meropenem and streptomycin. Three compounds (2, 4 and 5) showed antibacterial activity against E. coli. with MIC values from 12.5 to 25 µg/mL.