Neat carbomethoxypivaloylketene—preparation and chemical reactivity

Neat carbomethoxypivaloylketene, the first fairly persistent α-oxoketene stabilized both electronically as well as sterically, is generated by flash vacuum pyrolysis of the corresponding furan-2,3-dione. It adds primary amines to afford pivaloyl-malonic acid amides and undergoes hetero-Diels–Alder reactions to furnish usual and unusual [4+2] adducts. Some stereo- and regiochemical features are verified with aid of 2D NMR experiments and a X-ray structure analysis.