Biscyclopropyl titanocene: A novel reagent for the synthesis of alkylidene and vinyl cyclopropanes
Alkylidene cyclopropane derivatives are obtained by reaction of biscyclopropyl titanocene with several types of carbonyl compounds, including aldehydes, ketones and esters. In some cases the isomeric vinyl cyclopropane products are also obtained. Biscyclopropyl titanocene also reacts with alkynes forming, after acidification, the corresponding vinyl cyclopropanes.
Highly Enantioselective Construction of Strained Spiro[2,3]hexanes through a Michael Addition/Ring Expansion/Cyclization Cascade
We herein report a general organocatalytic enantioselective strategy for the construction of highly strained spiro[2,3]hexane skeletons from methylenecyclopropanes and a broad selection of α,β-unsaturated aldehydes. The reaction proceeds through a Michael addition followed by ring expansion of methylenecyclopropanes and nucleophilic attack of an enamine to realize the construction of spiro[2,3]hexanes. Key to the success of this approach are the utilization of an electron-deficient difluoro-substituted secondary amine catalyst and the intrinsic reactivity of methylenecyclopropanes.
Synthesis of Fluorinated Homoallylic Compounds by Fluoroalkyl Radical Mediated Ring Opening of Methylenecyclopropanes
The fluoroalkyl (Rf) radical mediated ring opening of methylenecyclopropanes (MCPs) 1 and subsequent atom transfer were investigated. In the first part, a copper-initiated radical reaction of Rf-X (X = I, Br) with MCP 1 gave homoallylic halides 2 in excellent yields. Similarly, radical reaction of the RfTMS/CsF/PhI(OCOR)2 system with MCP 1 led to homoallylic alcohol esters 3 in moderate to good yields. An efficient synthesis of fluoroalkyl (Rf)-substituted homoallylic halides 2 and homoallylic alcohol esters 3 by fluoroalkyl radical mediated ring opening of methylenecyclopropanes (MCPs) 1 followed by an atom-transfer process is developed.
Xie, Huajun,Xu, Bo
supporting information
p. 2594 - 2598
(2016/06/08)
Organoselenium-Catalyzed Oxidative Ring Expansion of Methylenecyclopropanes with Hydrogen Peroxide
Catalyst screening and optimization of reaction conditions allowed control of the organoselenium-catalyzed oxidative ring expansion of highly active methylenecyclopropanes to give substituted cyclobutanones selectively. This protocol employs H2O2 as a clean oxidant and generates no waste and, therefore, provides green access to useful, but not readily available, substituted cyclobutanones under mild conditions.
Yu, Lei,Chen, Fenglin,Ding, Yuanhua
p. 1033 - 1037
(2016/04/05)
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