D. Passarella et al., Cyclodimerization of indol-2-ylacetylenes. An example of intermolecular enyne-alkyne cycloaddition, J CHEM S P1, (2), 2001, pp. 127-129
Cyclodimerization of methyl 3-(indol-2-yl)propiolate 1 and 2-(indol-2-yl)-1
-(phenylsulfonyl)acetylene 2 proceeds through an enyne-alkyne cycloaddition
to give 4-(indol-2-yl)carbazoles.