Dimerization of 1-vinyl-4,5,6,7-tetrahydroindole in the presence of acids

In the presence of Bronsted and Lewis acids, I-vinyl-4,5,6,7-tetrahydroindole is transformed into its dimes, 1-vinyl-2-[1-(4,5,6,7-tetrahydroindolyl)ethyl]-4,5,6,7-tetrahydroindole, and polymers containing units of the dimer and segments of oxidized tetrahydroindole cycles.