3-Chlor-4-hydroxy-3-cyclobuten-1,2-dion

2,2,3-trimethoxy-3-cyclobuten-1-one

2,3,4-tris[(2-methylpropan-2-yl)oxy]cyclobut-2-en-1-one

2-Cyclobuten-1-one, 2,3-bis(1,1-dimethylethoxy)-4-hydroxy-