Synthesis of Functionalized 1,2,3,4‐Tetrahydro‐β‐carbolines from Enamino Ketones

Reaction of tryptamine ( 1 ) with 2 and 3 gives the enamino ketones 4a and 5 , resp., which on treatment with trifluoroacetic acid lead to the 2‐substituted indoles 8 and 9 , respectively. Acylation of 4a followed by reaction with trifluoroacetic acid or a Lewis acid affords the 1,2,3,4‐tetrahydro‐β‐carbolines 7b–e in excellent yields. Treatment of 8 with anhydrides like (CF 3 CO) 2 O also yields the 1,2,3,4‐tetrahydro‐β‐carboline 7f . The trichloromethylcarbonyl group in 7 can easily be converted into an ester moiety by reaction with an alcohol in the presence of K 2 CO 3 .