methyl 3-oxo-4-phenylmethoxybutanoate

methyl 4-acetyloxy-3-oxobutanoate

prop-2-enyl 4-chloro-3-oxobutanoate

methyl 3-oxo-4-(triphenyl-λ⁵-phosphanylidene)butanoate

methyl 2-(4H-1,4-benzothiazin-3-ylidene)acetate