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DOI: 10.1055/s-0029-1219873
Copper-Catalyzed Synthesis of Aza-Fused Polycyclic Quinolines
Q. Cai*, Z. Li, J. Wei, L. Fu, C. Ha, D. Pei, K. Ding*
Guangzhou Institutes of Biomedicine and Health and Guangzhou Institute of Chemistry, P. R. of China
Publication History
Publication Date:
20 May 2010 (online)
Significance
Reported here is the synthesis of benzimidazo[1,2-a]quinolines as well as imidazo- and pyrrolo-fused quinolines via a copper-catalyzed cascade reaction. Using 2-iodobenzaldehyde and 2-(1H-benzo[d]imidazole-2-yl)acetonitrile (R¹ = CN) as starting materials, a screening of conditions showed that CuI as catalyst, l-proline as ligand, and K2CO3 as base gave the optimal yield (91%). The scope was then extended to a variety of 2-iodo- and 2-bromobenzaldehydes as well as bromo heteroaromatics to afford benzimidazo[1,2-a]quinolines in good to excellent yields, although it is necessary to heat at 50 ˚C for electron-rich benzaldehydes and at 80 ˚C for bromobenzaldehydes. The less reactive chlorobenzaldehydes required heating at 110 ˚C to achieve modest yields. Imidazoles and pyrroles afforded the corresponding aza-fused quinolines in low to good yields.