State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 345 Lingling Road, Shanghai 200032, P. R. China.
Acc Chem Res. 2012 Apr 17;45(4):641-52. doi: 10.1021/ar200237z. Epub 2011 Dec 13.
Although they are highly strained, methylenecyclopropanes (MCPs) are readily accessible molecules that have served as useful building blocks in organic synthesis. MCPs can undergo a variety of ring-opening reactions because the release of cyclopropyl ring strain (40 kcal/mol) can provide a thermodynamic driving force for reactions and the π-character of the bonds within the cyclopropane can afford the kinetic opportunity to initiate the ring-opening. Since the 1970s, the chemistry of MCPs has been widely explored in the presence of transition metal catalysts, but less attention had been paid to the Lewis or Brønsted acid mediated chemistry of MCPs. During the past decade, significant developments have also been made in the Lewis or Brønsted acid mediated reactions of MCPs. This Account describes chemistry developed in our laboratory and by other researchers. Lewis and Brønsted acids can be used as catalysts or reagents in the reactions of MCPs with a variety of substrates, and substituents on the terminal methylene or on the cyclopropyl ring of MCPs significantly affect the reaction pathways. During the past decade, we and other researchers have found interesting transformations based on this chemistry. These new reactions include the ring expansion of MCPs, cycloaddition reactions of MCPs with aldehydes and imines, cycloaddition reactions of MCPs with nitriles in the presence of strong Brønsted acid, radical reactions of MCPs with 1,3-dicarbonyl compounds, intramolecular Friedel-Crafts reactions of MCPs with arenes, acylation reactions of MCPs, and the reaction of MCPs with 1,1,3-triarylprop-2-yn-1-ols or their methyl ethers. These Lewis or Brønsted acid mediated reactions of MCPs can produce a variety of new compounds such as cyclobutanones, indenes, tetrahydrofurans, and tetrahydroquinolines. Finally, we have also carried out computational studies to explain the mechanism of the Brønsted acid mediated reactions of MCPs with acetonitrile.
尽管亚甲基环丙烷（MCP）张力很大，但它们还是很容易得到的分子，并且已被用作有机合成中的有用构建块。MCP 可以经历各种开环反应，因为释放环丙基环张力（40 kcal/mol）可以为反应提供热力学驱动力，并且环丙烷中键的π特性可以提供引发开环的动力学机会。自 20 世纪 70 年代以来，MCP 在过渡金属催化剂存在下的化学性质已得到广泛研究，但对 MCP 的路易斯或布朗斯台德酸介导化学性质的关注较少。在过去的十年中，MCP 的路易斯或布朗斯台德酸介导反应也取得了重大进展。本说明描述了我们实验室和其他研究人员开发的化学。路易斯和布朗斯台德酸可以用作 MCP 与各种底物反应的催化剂或试剂，并且 MCP 末端亚甲基或环丙基上的取代基会显著影响反应途径。在过去的十年中，我们和其他研究人员已经发现了基于此化学的有趣转化。这些新反应包括 MCP 的环扩张、MCP 与醛和亚胺的环加成反应、强布朗斯台德酸存在下 MCP 与腈的环加成反应、MCP 与 1,3-二羰基化合物的自由基反应、MCP 与芳烃的分子内傅克反应、MCP 的酰化反应以及 MCP 与 1,1,3-三芳基丙-2-炔-1-醇或其甲酯的反应。这些 MCP 的路易斯或布朗斯台德酸介导反应可以生成各种新化合物，如环丁酮、茚、四氢呋喃和四氢喹啉。最后，我们还进行了计算研究，以解释 MCP 与乙腈的布朗斯台德酸介导反应的机理。
