diethyl (2Z)-2-(furan-2-ylmethylidene)butanedioate

tetraethyl butane-1,1,2,3-tetracarboxylate

diethyl 2-bromobutanedioate

diethyl 2-(2-methylaziridin-1-yl)butanedioate

diethyl 2-(4,4-dimethylpent-2-ynyl)butanedioate