Acid-Promoted Nucleophilic Substitution Reaction

The unprecedented nucleophilic substitution reaction on the indole nitrogen N(1) was discovered when 1-hydroxyindoles were reacted with good nucleo-philes in 85% HCOOH [1-7]. Since then, this type of reaction has been widely observed among the reactions of 1-hydroxytryptamine derivatives and many examples have been accumulated.

Upon reaction with indole as a good nucleophile, (dl)-1-hydroxytrypto-phan methyl ester (dl-41) and 1-propyloxy-Nb-methoxycarbonyltryptamine (53b) provide the corresponding 1-(indol-3-yl)indoles, 133 (51%) and 134 (38%), respectively (Scheme 17) [37]. Neither the introduction of a sterically hindered group on the Nb-position nor the existence of a substituent on the



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