Syntheses of 4-, 5-, 6-, and 7-substituted tryptamine derivatives and the use of a bromine atom as a protecting group

Orthogonal syntheses of 4-, 5-, 6-, and 7-chloro substituted tryptamine derivatives were performed under the Grandberg–Zuyanova-modified Fisher indole-synthesis conditions. In the 4- and 6-substituted tryptamine cases, a bromine atom was utilized as an easily cleavable protecting group, which allowed complete regiocontrol. In addition, a chlorine substituent was preserved in the debromination step and could be utilized as a synthetic handle for late-stage diversification under modern Pd(0) catalysis conditions.