Two routes for the synthesis of N‐ethyl‐N‐(4‐nitrophenylsulfonyl)‐α,β‐dehydroamino acid derivatives from serine, threonine and phenylserine derivatives are presented. One route consists of dehydration of N‐(4‐nitrophenylsulfonyl)‐β‐hydroxyamino acid esters with di‐tert‐butyl dicarbonate catalyzed by 4‐(dimethylamino)pyridine, followed by alkylation of the N‐(4‐nitrophenylsulfonyl)‐α,β‐dehydroamino acid methyl esters obtained with triethyloxonium tetrafluoroborate. The second strategy applied the same procedures but in inverse order: alkylation followed by dehydration. These methods made it possible to obtain for the first time, new non‐natural amino acids, which incorporate both an N‐ethyl and an α,β‐dehydro moiety.