Synthesis and structure of a heterocyclic ansa pyrrole amino acid

Abstract

We report a synthetic route to ansa pyrrole amino acids via olefin ring-closing metathesis of diene precursors in the presence of Grubbs I
catalyst. The dienes were prepared by Grignard addition to pyrrole sulfinyl imines. The success of the macrocyclic ring closure depends on
the dienes structure and only in the case of the 13-membered compound 28 sufficient material could be isolated by preparative HPLC separation
to investigate its structure spectroscopically. As also rationalized by our computations at the B3LYP/6-311þG(d,p)//B3LYP/6-31G(d) level of
theory, 28 is configurationally stable.