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Abstract
(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image)
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.