95062-98-9Relevant academic research and scientific papers
Mechanistic Studies on a Cu-Catalyzed Asymmetric Allylic Alkylation with Cyclic Racemic Starting Materials
Rideau, Emeline,You, Hengzhi,Sidera, Mireia,Claridge, Timothy D. W.,Fletcher, Stephen P.
, p. 5614 - 5624 (2017)
Mechanistic studies on Cu-catalyzed asymmetric additions of alkylzirconocene nucleophiles to racemic allylic halide electrophiles were conducted using a combination of isotopic labeling, NMR spectroscopy, kinetic modeling, structure-activity relationships, and new reaction development. Kinetic and dynamic NMR spectroscopic studies provided insight into the oligomeric Cu-ligand complexes, which evolve during the course of the reaction to become faster and more highly enantioselective. The Cu-counterions play a role in both selecting different pathways and in racemizing the starting material via formation of an allyl iodide intermediate. We quantify the rate of Cu-catalyzed allyl iodide isomerization and identify a series of conditions under which the formation and racemization of the allyl iodide occurs. We developed reaction conditions where racemic allylic phosphates are suitable substrates using new phosphoramidite ligand D. D also allows highly enantioselective addition to racemic seven-membered-ring allyl chlorides for the first time.1H and2H NMR spectroscopy experiments on reactions using allylic phosphates showed the importance of allyl chloride intermediates, which form either by the action of TMSCl or from an adventitious chloride source. Overall these studies support a mechanism where complex oligomeric catalysts both racemize the starting material and select one enantiomer for a highly enantioselective reaction. It is anticipated that this work will enable extension of copper-catalyzed asymmetric reactions and provide understanding on how to develop dynamic kinetic asymmetric transformations more broadly.
Substituent Effects on the Intramolecular Photochemical Reactions of Phenyl-Ethenyl Non-conjugated Bichromophoric Systems
Ellis-Davies, Graham C. R.,Gilbert, Andrew,Heath, Peter,Lane, Jon C.,Warrington, John V.,Westover, David L.
, p. 1833 - 1842 (2007/10/02)
The effects of substitution on the photochemistry of phenyl-ethenyl bichromophoric systems are reported.Methyl substitution at the 2-, 3-, 5-, and 1,1,2-positions in the pentene moiety of 5-phenylpent-1-ene reduces both reaction efficiency and selectivity but in contrast to intramolecular analogues the photoreaction of 3-phenethylcyclohexene is comparable with that of the corresponding cyclopentene.Incorporation of ester units in the connecting unit between the chromophores or on the ethene inhibits intramolecular cyclisation as does the presence of para OMe, CN, or COMe groups in 5-phenylpent-1-ene.In contrast reaction selectivity and efficiency are greatly promoted by ortho Me or OMe groups and the products reflect exlusive 1,3-cycloaddition.The presence of a para Me group in 5-phenylpent-1-ene leads to specific 2,6-intramolecular cyclisation but the reaction of the meta-Me derivative leads to four products derived from 1,3- and 1,5-intramolecular cycloaddition.The observations are discussed in terms of mechanisms of arene-ethene photoreactions and preferred conformations of the bichromophores.
