A direct entry and simple process for the synthesis of γ-spiroiminolactones present in a large number of natural products has been developed. In the first step, the synthesis of parabanic acid derivatives was commenced from the reaction of N,N-disubstituted urea and thiourea with oxalyl chloride, then a three-component reaction was carried out with isocyanides, acetylenic esters, and N,N-disubstituted parabanic acid derivatives. The method allows the construction of a variety of γ-spiroiminolactone structures in good to high yields starting from readily available precursors. It was found that in the case of N,N-diphenyl thioparabanic acid, additional products of γ-dispiroiminolactones have been formed due to the higher electrophilicity of α-dicarbonyl groups. The structures were fully established using spectroscopic analysis NMR, IR, and Mass spectrometry. The crystal structure of γ-dispiroiminolactone was confirmed from single-crystal Xray diffraction study.
