Asymmetric Synthesis of Unprotected Tryptophan Derivatives Using Gramines via Ni(II) Complexes

We herein report the synthesis of substituted tryptophans using Ni(II) complexes of glycine and gramines. This reaction proceeds under operationally convenient and mild conditions, using inexpensive, nontoxic, and easily accessible reagents. The reactions feature high yields and virtually complete thermodynamically controlled diastereoselectivity, providing a convenient method for the synthesis of tailor-made tryptophans.