Indium-catalyzed annulation of 2-aryl- and 2-heteroarylindoles with propargyl ethers: concise synthesis and photophysical properties of diverse aryl- and heteroaryl-annulated[a]carbazoles.

Treatment of 2-aryl- and 2-heteroarylindoles with propargyl ethers in the presence of a catalytic amount of indium nonafluorobutanesulfonate [In(ONf)(3)] gave aryl- and heteroaryl-annulated[a]carbazoles in good yields. The synthetically attractive feature is reflected by its applicability to a wide range of 2-aryl- and 2-heteroarylindoles. In the annulation reaction, propargyl ethers act as C3 sources (HC[triple bond]C-CH(2)OR).