85267-86-3Relevant academic research and scientific papers
Selective Double Carbomagnesiation of Internal Alkynes Catalyzed by Iron-N-Heterocyclic Carbene Complexes: A Convenient Method to Highly Substituted 1,3-Dienyl Magnesium Reagents
Liu, Yuesheng,Wang, Lijun,Deng, Liang
supporting information, p. 112 - 115 (2016/01/25)
Controlled multicarbometalation of alkynes has been envisaged as an efficient synthetic method for dienyl and polyenyl metal reagents, but an effective catalyst enabling the transformation has remained elusive. Herein, we report that an iron(II)-N-heterocyclic carbene (NHC) complex (IEt2Me2)2FeCl2 (IEt2Me2 = 1,3-diethyl-4,5-dimethylimidazol-2-ylidene) can serve as a precatalyst for the double carbometalation of internal unsymmetrical alkynes with alkyl Grignard reagents, producing highly substituted 1,3-dienyl magnesium reagents with high regio- and stereoselectivity. Mechanistic studies suggest the involvement of low-coordinate organoiron(II)-NHC species as the in-cycle intermediates. The strong σ-donating nature of IEt2Me2 and its appropriate steric property are thought the key factors endowing the iron-NHC catalyst fine performance.
Studies Dealing with the Cycloreversion Reactions of Phenyl-Substituted 2,3-Diazabicyclohex-2-enes
Padwa, Albert,Kumagai, Tsutomu,Tohidi, Mahrokh
, p. 1834 - 1840 (2007/10/02)
A study of the reactivity of 2-diazopropane with a series of diphenyl-substituted cyclopropenes has been carried out.The cycloadditions afford 1,5-diphenyl-2,3-diazabicyclohex-2-enes in high yield.Thermolysis of the diazabicyclohexene system for extended periods of time afforded a mixture of 1,3-dienes as well as a substituted bicyclobutane.By studying the distribution of products as a function of time it was possible to show that the 2,3-diazabicyclohexene system first rearranges to an isomeric 1,2-diazabicyclohex-2-ene.This reaction was attributed to an initial cycloreversion to produce a diazoalkene.Attack of the terminal nitrogen atom of the initially generated diazo group onto the neighboring double bond affords the bicyclic aziridine system.Reasonable mechanistic options for the 1,1-cycloaddition include a concerted pathway or a stepwise process.On further heating the 1,2-diazabicyclohexene ring regenerates the allyl-substituted diazoalkane.Loss of nitrogen produces a carbene which undergoes a hydrogen or vinyl shift to give the observed dienes.The formation of the bicyclobutane ring can be viewed in terms of a process involving initial C-N bond cleavage of the 2,3-diazabicyclohexene to yield a diazenyl radical followed by nitrogen loss and radical coupling.In contrast to the thermal results, direct irradiation of the 2,3-diazabicyclohexene results in a cycloreversion to give a 3,4-diaza-substituted 1,3,5-hexatriene derivative.The results obtained indicate that the total mechanistic picture for the thermal and photochemical decomposition of bicyclic pyrazolines can be changed dramatically by the presence of phenyl substituents.
