Tenuazonic acid derivatives were synthesized from amino acid esters by N-acetoacetylation with diketene followed by cyclization with sodium alkoxides. Some L-amino acid produced a small amount of DL-compounds in this process. N-Acetoacetyl group of diethyl aspartate cyclized to the α-ester group to form five-membered ring compound selectively. These compounds were condensed with carbonyl reagents.