Reductions of Aromatic Amino Acids and Derivatives

Abstract

Catalytic reduction of phenylalanine and phenylglycine derivatives can be achieved with rhodium on carbon or alumina to give good yields of the corresponding cyclohexyl derivatives. The procedure can be scaled.

Platinum‐Catalyzed Facile Arene Hydrogenation: Dramatic Effect of Activated Carbon and Vinylsiloxane Derivatives on the Catalyst Efficiency

“…On the other hand, hydrogenation of glycidyl phenyl ether, 3‐phenylpropionitrile, and α‐ethylfuran afforded the complicated mixtures because of the side reactions also proceeded such as ring‐opening reaction of epoxido‐ and tetrahydrofuran moieties, and reduction of nitrile group followed by dimerization. One of the molecular designs of functional materials and pharmaceuticals is replacement of “aromatic” phenyl to the “non‐aromatic” cyclohexyl group for increasing of hydrophobic interaction and steric hindrance, [11] and cyclohexylalanine (Cha), obtained by arene hydrogenation of phenylalanine, is known to be a typical case [12] . Although the reaction of phenylalanine did not proceed, acetamide derivative 1 o was hydrogenated in THF to afford the corresponding Cha derivative 2 o in 92 % yield (Entry 15).…”

“…One of the molecular designs of functional materials and pharmaceuticals is replacement of "aromatic" phenyl to the "non-aromatic" cyclohexyl group for increasing of hydrophobic interaction and steric hindrance, [11] and cyclohexylalanine (Cha), obtained by arene hydrogenation of phenylalanine, is known to be a typical case. [12] Although the reaction of phenylalanine did not proceed, acetamide derivative 1 o was hydrogenated in THF to afford the corresponding Cha derivative 2 o in 92 % yield (Entry 15). Piperidine core is also important fragment of pharmaceuticals and natural products.…”

Rhodium/Graphite-Catalyzed Hydrogenation of Carbocyclic and Heterocyclic Aromatic Compounds

“…17 Catalytic reductions of phenylglycine and phenylalanine derivatives were previously performed with 5% rhodium/ charcoal or rhodium/alumina to give excellent yields of the corresponding cyclohexyl derivatives under typical conditions of aqueous phosphoric, hydrochloric, or sulfuric acid, 60°C, 50 psi hydrogen, and 24 hours reaction time. 18 Similarly, aromatic-ring hydrogenations of (R)-3phenyllactic acid and (R)-3-phenylalanine were accomplished by using either 5% or 10% rhodium/charcoal in protic solvents at 4-15 bar hydrogen pressure. 19 10% Rhodium/charcoal was more active than analogous palladium, iridium, platinum, or ruthenium catalysts in the hydrogenation of arenes in water at 80°C and 3-5 atm of hydrogen pressure, 20 as well as in the hydrogenation of 1phenylethanol 13b or benzoic acid 21 in supercritical carbon dioxide at 50°C and 3-10 mPa of hydrogen pressure.…”