Reactions of 1-vinyl-4,5,6,7-tetrahydroindole and its mixtures with 4,5,6,7-tetrahydroindole in the presence of Cr- and Pd-coated catalysts

In the presence of Cr- and Pd-coated γ-alumina catalysts, 1-vinyl-4,5,6,7-tetrahydroindole (VTHI) and its mixtures with 4,5,6,7-tetrahydroindole (THI) are converted into 1-ethyl-4,5,6,7-tetrahydroindole (1-ETHI), indole, and 2-ethylindole, in proportions dependent on the reaction conditions and the catalyst. Over a sulfided 1% Pd-γ-alumina catalyst in the presence of hydrogen at 200°C, VTHI is converted into 1-ETHI and THI. When the temperature is raised to 300–350°C, indole is formed in addition to these products. A 1∶1 mixture of VTHI and THI over 1% Pd-γ-alumina at 300°C gives indole and 2-ethylindole, over a sulfided 1% Pd -γ-alumina catalyst at 200°C, 1-ETHI, and over a Cr oxide catalyst at 500°C, indole.