Asako Sobi, Kobashi Takaaki, Takai Kazuhiko
Division of Applied Chemistry, Graduate School of Natural Science and Technology , Okayama University , 3-1-1 Tsushimanaka , Kita-ku, Okayama 700-8530 , Japan.
J Am Chem Soc. 2018 Nov 14;140(45):15425-15429. doi: 10.1021/jacs.8b09297. Epub 2018 Nov 2.
Cyclopropanation of alkenes is a well-established textbook reaction for the synthesis of cyclopropanes, where a "high-energy" carbene species is exploited to drive the reaction forward. However, little attention has been focused toward molecular transformations involving the reverse reaction, retro-cyclopropanation (RC). This is because of difficulties associated with both cleaving the two geminal C-C single bonds and exploiting the generated carbenes for further transformations in an efficient and selective manner. Here, we report that a molybdenum-based catalytic system overcomes the above challenges and effects the RC of cyclopropanes bearing a pyridyl group with the release of ethylene (alkene) and the subsequent intramolecular cyclization leading to pyrido[2,1- a]isoindoles. The reaction allows for the uncommon use of cyclopropanes as C1 synthetic units in contrast to most conventional reactions in which cyclopropanes are used as C3 synthetic units. We anticipate that this new strategy will pave the way for C1 cyclopropane chemistry.
烯烃的环丙烷化反应是合成环丙烷的一种经典教科书反应，其中利用“高能”卡宾物种推动反应进行。然而，涉及逆反应——逆环丙烷化（RC）的分子转化很少受到关注。这是因为切断两个偕二碳 - 碳单键以及以高效且选择性的方式利用生成的卡宾进行进一步转化都存在困难。在此，我们报道一种基于钼的催化体系克服了上述挑战，实现了带有吡啶基的环丙烷的逆环丙烷化反应，释放出乙烯（烯烃），随后发生分子内环化生成吡啶并[2,1 - a]异吲哚。与大多数将环丙烷用作C3合成单元的传统反应相比，该反应允许将环丙烷作为C1合成单元进行不常见的应用。我们预计这种新策略将为C1环丙烷化学开辟道路。
