Cyclobutadiene Controversy

For years cyclobutadiene has been called the “Mona Lisa of organic chemistry” because the seemingly inscrutable chemical resisted efforts to reveal its crystal structure, despite a deceivingly simple molecular formula. Cyclobutadiene is now also a source of controversy because some researchers are calling into question the first reported X-ray crystal structure of the molecule, which was published in a research paper in Science in July (C&EN, July 19, page 33). Mihail Barboiu and colleagues at the European Institute of Membranes, in Montpellier, France, described how they trapped 4,6-dimethyl-α-pyrone in a guanidinium-sulfonate-calixarene network and then zapped crystals of the complex repeatedly with ultraviolet light to convert the precursor pyrone into CO₂ and 1,3-dimethylcyclobutadiene. In separate peer-reviewed technical comments in Science, David Scheschkewitz of Imperial College London and a group of researchers led by Igor V. Alabugin of Florida State University argue that Barboiu and colleagues didn’t make 1,3-dimethylcyclobutadiene but instead crystallized 4,6-dimethyl-β-lactone, an intermediate of the photolysis reaction (DOI: 10.1126/science.1195752; 10.1126/sci ence.1196188). Barboiu and colleagues stand by their initial interpretation of the crystallography data in a response also published in Science (DOI: 10.1126/sci ence.1195846).