Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-3290, USA.
J Org Chem. 2010 Oct 1;75(19):6317-25. doi: 10.1021/jo1010735.
This Perspective details a developing research program that emerged from simple plans for achieving the synthesis of tetrahydrofurans from cyclopropanes and C═O π bonds. Lewis acid catalyzed annulations of malonate-derived donor-acceptor cyclopropanes with aldehydes are unusually broad in scope and lead to the synthesis of structurally diverse tetrahydrofurans. The reactions are stereospecific, with inversion observed at the cyclopropane donor site. Substituent effects on the aldehyde suggest that it acts as a nucleophile in the reaction. An unusual mechanism emerges in which the aldehyde traps a configurationally stable intimate ion pair to stereospecifically construct the C-O bond. In addition to the stereospecific conversion of enantiomerically enriched cyclopropanes into nonracemic heterocycles, we have also demonstrated that racemic cyclopropane 1,1-diesters can undergo dynamic kinetic asymmetric annulations catalyzed by (pybox)MgI(2) complexes. Asymmetric syntheses of (+)-polyanthellin A and (+)-virgatusin have been achieved; both rely upon cyclopropane/aldehyde annulation for construction of the core tetrahydrofurans.
本文详细介绍了一个不断发展的研究计划，该计划源于将环丙烷和 C═Oπ键合合成四氢呋喃的简单计划。丙二酸酯衍生的给体-受体环丙烷与醛的路易斯酸催化环加成反应具有非常广泛的范围，可导致结构多样的四氢呋喃的合成。这些反应具有立体特异性，在环丙烷供体位点观察到反转。醛上的取代基效应表明其在反应中充当亲核试剂。一个不寻常的机制出现了，其中醛捕获了一个构象稳定的内离子对，以立体特异性地构建 C-O 键。除了对映体富集的环丙烷立体特异性转化为非外消旋杂环外，我们还证明了外消旋环丙烷 1,1-二酯可以通过（pybox）MgI（2）配合物催化的动态动力学不对称环加成反应。（+）-多安替林 A 和（+）-virgatusin 的不对称合成已经实现；两者都依赖于环丙烷/醛环加成来构建核心四氢呋喃。
