One-pot synthesis of -spiroiminolactones and -dispiroiminolactones using -disubstituted parabanic acid and thioparabanic acid derivatives

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