Cyclic tautomers of tryptophans and tryptamines. VI. Preparation of Na-alkyl-,5-chloro-, and 5-nitrotryptophan derivatives.

Selective Na-alkylation, 5-chlorination, 5-bromination, and 5-nitration of tryptophan derivatives were achieved. The alkylation of the cyclic tautomer 2 of Nb-methoxycarbonyl-DL-tryptophan methyl ester (1) with alkyl halides in acetone-K2CO3 gave the Na-alkyl derivatives (3a and 4) in excellent yields. The chlorination of the cyclic tautomer 3b with NCS-AcOH gave the 5-chloro derivative (5b) in 89% yield, and this was readily converted to the 5-chlorotryptophan derivatives (7a, 7b, 9). The similar chlorination of 12 gave the 5-chloro derivatives (13a, 15a) and the 3a-chloropyrroloindole derivative (17). On the other hand the bromination of 12 with NBS-AcOH gave the 5-bromo derivative (13b) in good yield, and this was readily converted to 15d and further to 15c. The nitration of 3b and 12 with fuming nitric acid also gave the 5-nitro derivatives (5c, 7c, 13c, 15e) in excellent yields.