Spirofluorenyl-1,2,4-oxadiazinan-5-ones are prepared in good to excellent yields through metal-free [3+3] cycloaddition of N-vinyl fluorenone nitrones and aza-oxyallyl cations under mild reaction conditions. Detailed studies reveal that N-vinyl fluorenone nitrones show greater reactivity in [3+3] cycloadditions with aza-oxyallyl cations compared to N-alkyl/aryl fluorenone nitrones. The spirofluorenyl-1,2,4-oxadiazinan-5-ones are easily prepared on gram scale. The present method features mild reaction conditions, broad substrate scope, good functional group tolerance and efficient [3+3] cycloadditions of 9-fluorenone nitrones.

中文翻译：

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通过无金属[3 + 3]与氮杂-氧烯丙基阳离子的N-乙烯基芴酮亚硝基环加成反应合成螺芴基-1,2,4-恶二嗪酮-5-酮

通过在温和的反应条件下，通过无金属的N-乙烯基芴酮硝酮和氮杂-氧烯丙基阳离子的[3 + 3]环加成反应，可以制备出高至优异收率的螺芴基-1,2,4-恶二嗪酮-5-酮。详细的研究表明，与N-烷基/芳基芴酮硝酮相比，N-乙烯基芴酮硝酮在具有氮杂-烯丙基烯丙基阳离子的[3 + 3]环加成物中显示出更高的反应性。螺芴基-1,2,4-氧杂二氮杂-5-酮很容易以克为单位制备。本方法的特点是反应条件温和，底物范围宽，官能团耐受性好和9-芴酮硝酮的有效[3 + 3]环加成反应。