Cyclodimerization of methyl 3-(indol-2-yl)propiolate 1 and 2-(indol-2-yl)-1-(phenylsulfonyl)acetylene 2 proceeds through an enyneâalkyne cycloaddition to give 4-(indol-2-yl)carbazoles.
Methyl indol-2-ylpropiolate 1 is synthesized by using a catalyst system of PPh3–CuI in the presence of K2CO3 as base. The procedure appears convenient if compared with Pd-catalyzed cross-coupling reactions. The interest is increased by the use of an alk-1-yne containing an electron-withdrawing group.