Asymmetric synthesis of the central tryptophan residue of stephanotic acid

Abstract

The C-6 substituted tryptophan di- and tri-peptides 5 and 6, representing the tryptophan core of stephanotic acid, have been synthesized, the key steps being the formation of the phosphono-di- and tri-peptides 8 and 10 by a highly chemoselective rhodium(II) catalyzed carbene N-H insertion reaction, their subsequent Horner–Wadsworth–Emmons reactions with N-Boc-6-bromoindole-3-carboxaldehyde, and the rhodium(I) catalyzed asymmetric hydrogenation of the resulting dehydro di- and tri-peptides.