Decatungstate-Photocatalyzed Functionalization of α-Imino Esters for the Preparation of Unnatural α-Amino Acid Derivatives

A library of unnatural a-amino acid derivatives has been prepared via the hydrofunctionalization of the C=N bond in a set of compounds belonging to the family of a-imino esters. The devised methodology capitalizes on the use of tetrabutylammonium decatungstate as the photocatalyst to generate C-centered radicals from aliphatic and aromatic aldehydes, cyclic and acyclic oxygenated compounds and even cycloalkanes, via a hydrogen atom transfer (HAT) step. The best performance was observed when a-hydrazono esters were employed in the role of radical traps, which delivered the corresponding (protected) a-hydrazino acids as products. The versatility of the protocol was further demonstrated by the possibility to functionalize the herbicide safener isoxadifen-ethyl.

Automated summary

A library of unnatural a-amino acid derivatives was synthesized by hydrofunctionalization of the C=N bond in a series of compounds. Tetrabutylammonium decatungstate was used as the photocatalyst to generate C-centered radicals, leading to the formation of (protected) a-hydrazino acids as products. This methodology proved to be versatile, allowing functionalization of the herbicide safener isoxadifen-ethyl.