On the Asymmetric Iridium-Catalyzed N-Allylation of Amino Acid Esters: Improved Selectivities through Structural Variation of the Chiral Phosphoramidite Ligand

Abstract

The investigation of the iridium-catalyzed asymmetric N-allylation of tert-butyl glycinate using a “branched” racemic 1-vinyl-alkyl methyl carbonate revealed severe limitations of existing protocols. By screening a set of 24 BINOL-derived chiral phosphoramidites a new superior ligand (L24*) was identified which afforded the amination product with high enantioselectivity (≥95 % ee) under optimized conditions. This ligand also allowed the N-allylation of other amino acid tert-butyl esters (derived from alanine, phenylalanine, or proline) with outstanding levels of diastereocontrol (d.r. ≥99 : 1) and negligible matched/mismatched differences.