Ytterbium triflate catalyzed electrophilic substitution of indoles: the synthesis of unnatural tryptophan derivatives

Abstract Benzylamine was combined with ethyl glyoxylate to form the intermediate imine which in the presence of catalytic amount of Yb(OTf) 3 underwent electrophilic substitution on the 3-position of a variety of indoles to produce unnatural tryptophan derivatives. Penicillin-G-acylase mediated N -acylation produced optically active tryptophan derivatives.