Cycloaddition of Huisgen 1,4-dipoles: synthesis and rapid epimerization of functionalized spiropyrido[2,1-<i>b</i>][1,3]oxazine-pyrroles and related products
作者:Andrew R. Galeev、Anna A. Moroz、Maksim V. Dmitriev、Andrey N. Maslivets
DOI:10.1039/d1ra08384h
日期:——
cycloaddition has emerged as a powerful tool for the synthesis of various cyclic compounds. In the present work, 1H-pyrrole-2,3-diones are proposed as new dipolarophiles for 1,4-dipolar cycloaddition. Their [4 + 2] cycloaddition with dipoles generated from dimethyl acetylenedicarboxylate and pyridine was found to proceed regioselectively affording spiro[pyrido[2,1-b][1,3]oxazine-2,3'-pyrroles] as diastereomeric
1,4-偶极环加成已成为合成各种环状化合物的有力工具。在目前的工作中,1H-吡咯-2,3-二酮被提议作为1,4-偶极环加成反应的新亲偶极试剂。发现它们与乙炔二甲酸二甲酯和吡啶产生的偶极子发生[4 + 2]环加成,区域选择性地进行,得到螺[吡啶并[2,1-b][1,3]恶嗪-2,3'-吡咯]作为非对映异构体混合物,其存在在溶液中快速平衡。经证实,这种快速差向异构化现象是其他类似螺吡啶并[2,1-b][1,3]恶嗪甚至相关螺喹嗪的特征,这一点通过对先前报道的相关产品的研究得到证实,并在这项工作,1,4-偶极环加成反应。