Organocatalytic Decarboxylation of Amino Acids as a Route to Bio‐based Amines and Amides

Abstract

AbstractAmino acids obtained by fermentation or recovered from protein waste hydrolysates represent an excellent renewable resource for the production of bio‐based chemicals. In an attempt to recycle both carbon and nitrogen, we report here on a chemocatalytic, metal‐free approach for decarboxylation of amino acids, thereby providing a direct access to primary amines. In the presence of a carbonyl compound the amino acid is temporarily trapped into a Schiff base, from which the elimination of CO2 may proceed more easily. After evaluating different types of aldehydes and ketones on their activity at low catalyst loadings (≤5 mol%), isophorone was identified as powerful organocatalyst under mild conditions. After optimisation many amino acids with a neutral side chain were converted in 28–99 % yield in 2‐propanol at 150 °C. When the reaction is performed in DMF, the amine is susceptible to N‐formylation. This consecutive reaction is catalysed by the acidity of the amino acid reactant itself. In this way, many amino acids were efficiently transformed to the corresponding formamides in a one‐pot catalytic system.