Olefins are among the most abundant and widely available chemical feedstock, indispensable for both the synthetic and biological communities due to their unique reactivity profile. Thus, hydrogenation and hydrofunctionalisation of C-C double bonds are important transformations to access pharmaceutical and chemical compounds that are produced at an industrial scale [1]. The photocatalytic reduction opens a path for the development of greener and safer hydrogenation methodologies, avoiding the use of high-energy, strong reductants as well as the use of pressure equipment. We have developed wide-scope, efficient protocols using Ir-based photocatalysts for the reduction and regioselective hydroaminoalkylation of electron-deficient alkenes [2].
Radical addition to α,β-unsaturated carbonyl compounds has been widely investigated as a useful method for functionalisation at the β-position [3]. The α-aminoalkyl radicals formed by photocatalytic oxidation are highly nucleophilic and consequently prone to attack electron deficient alkenes at β-position via Giese-type reaction. There are examples of stereoselectivity control for this reaction, but regioselectivity is completely predetermined by the nature of the substrate. As a result of our research we were able to direct radical addition to the α-position of α,β-unsaturated esters to produce potentially valuable β-amino acids. Importantly, our method overcomes relevant scope limitations of alternative approaches to these products, such as Mannich-type reactions.
Natalia A. Larionova, Jun Miyatake Ondozabal, Emily G. Smith, Xacobe C. Cambeiro*
School of Biological and Chemical Sciences – Queen Mary University of London
[1] H.-U. Blaser, F. Spindler and M. Thommen, in The Handbook of Homogeneous Hydrogenation, eds. J. G. de. Vries and C. J. Elsevier, Wiley-VCH, Weinheim, 2007, p. 1279.
[2] N. A. Larionova, J. Miyatake Ondozabal and X. C. Cambeiro. Reduction of electron-deficient alkenes enabled by a photoinduced hydrogen atom transfer. Advanced Synthesis & Catalysis, 2019, 10.1002/adsc.202000751.
[3] Some examples: a) A. Millet, Q. Lefebvre, and M. Rueping, Visible‐Light Photoredox‐Catalyzed Giese Reaction: Decarboxylative Addition of Amino Acid Derived α‐Amino Radicals to Electron‐Deficient Olefins, Chem.Eur.J. 2016, 22, p.13464; b) K. Nakajima, Y. Miyake, and Y. Nishibayashi, Synthetic Utilization of α‑Aminoalkyl Radicals and Related Species in Visible Light Photoredox Catalysis, Acc. Chem. Res. 2016, 49, p.1946.