Indole 7-ethoxycarbonyl-, ring synthesis

In the course of studies aimed at the development of a method for introducing substituents into the indole ring, Yokoyama et d. 61,62,65) succeeded in a simple synthesis of 4-bromodehydrotryptophan 131 by the vinylation of N-tosyl 4-bromoindole (124) in the presence of a stoichiometric amount of palladium salt Vinylation of fV-acetyldehydroalanine methyl ester 127 and N-(ethoxycarbonyl)dehydroalanine methyl ester 222 with 124 occurred in the presence of a stoichiometric amount of PdClj to give the corresponding 4-bromodehydrotryptophan 223 and 224, respectively. This result opened the route for a simple synthesis of tryptophan derivatives. Actual preparation of the 4-bromotryptophan 133 was achiev by the vinylation of 4-bromoindole 124 with the V-Boc-dehydroalanine methyl ester 130 in die presence of a stoichiometric amount of Pd(OAc)2. The literature conditions [1.0 equiv. of... 

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