Regiospecific Bromination of 3-Methylindoles with NBS and Its Application to the Concise Synthesis of Optically Active Unusual Tryptophans Present in Marine Cyclic Peptides(1).
A regiospecific bromination of substituted 3-methylindoles at either the C(3) alkyl moiety or the C(2) position was achieved via a free radical bromination or electrophilic process, respectively. The regiospecificity of the bromination could be controlled by variation of both the substituent and the N(1) protecting group on the indole ring. In addition, enantiospecific syntheses of 5-methoxytryptophan (20) and 5-hydroxy-6-chlorotryptophan (21c) as well as concise syntheses of optically active 2-bromotryptophan ethyl esters 26a,b or their substituted derivatives in three steps from bifunctional dibromoindoles were achieved via the above regiospecific process.
Liu
Ruiyan
R
Department of Chemistry, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin 53211.
Zhang
Puwen
P
Gan
Tong
T
Cook
James M.
JM