Practical and efficient preparation of the chiral 4-bromotryptophan derivative by Rh-catalyzed hydrogenation

An efficient three-step sequence has been developed for the preparation of a chiral 4-bromotryptophan derivative starting from the commercially available 4-bromoindole. Key to the synthesis was the generation of the chiral center via a Rh-catalyzed asymmetric hydrogenation of a dehydrotryptophan precursor with 95% yield and >99% ee. Notably, the whole synthetic route required no column chromatographic operations and was readily conducted on large scales.