New synthesis of polyfluoroalkyl racemic α-amino acids

We describe here a new synthesis of racemic α-amino acids containing polyfluorinated aliphatic long chain RF(CH2)3Y (RF = C2F5, C6F13, C8F17) (Y = CH(NH2)COOH) based on Sörensenʹs method. The radical addition of perfluoroalkyl iodides RFI (RF = C2F5, C6F13, C8F17) at room temperature to ethyl-2-carbetoxy-2-phthalimido-pent-4-enoate 3 was first initiated by Et3B/O2. Then, the reduction of adducts 4a–c using Et3B/O2/Bu3SnH leads to ethyl-2-carbetoxy-2-phthalimido-5-perfluoroalkyl-pentanoate 5a–c under mild conditions. Experimental conditions for optimisation of the iodoperfluoroalkylation step using Et3B/O2 were studied. Finally, deprotection of 5a–c gave the desired products 6a–c in good yields.