1099-45-2Relevant articles and documents
Cyclic Model for the Asymmetric Conjugate Addition of Organolithiums with Enoates
Nishimura, Katsumi,Fukuyama, Naoshi,Yamashita, Mitsuaki,Sumiyoshi, Takaaki,Yamamoto, Yasutomo,Yamada, Ken-Ichi,Tomioka, Kiyoshi
, p. 2256 - 2264 (2015)
The chiral diether ligand controlled asymmetric conjugate addition of organolithiums to nona-2,7-dienedioates preferentially proceeds via the s-cis conformation with coordination of the carbonyl oxygen atom to the lithium to give a lithium E-enolate intermediate. Subsequent intramolecular conjugate addition of the enolate also proceeds via a cyclic transition state involving the lithium and the s-cis-enoate, resulting in trans,trans-trisubstituted cyclohexanes with high enantiomeric excesses and yields.
Catalytic enantioselective carboannulation with allylsilanes
Ball-Jones, Nicolas R.,Badillo, Joseph J.,Tran, Ngon T.,Franz, Annaliese K.
, p. 9462 - 9465 (2014)
The first catalytic asymmetric carboannulation with allylsilanes is presented. The enantioselective [3+2] annulation is catalyzed using a scandium(III)/indapybox complex with tetrakis-[3,5-bis(trifluoromethyl)phenyl]- borate (BArF) to enhance catalytic activity and control stereoselectivity. Functionalized cyclopentanes containing a quaternary carbon center are derived from alkylidene oxindole, coumarin, and malonate substrates with high stereoselectivity. The enantioselective 1,4-conjugate addition and enantioselective lactone formation (by trapping of the β-silyl carbocation) is also described. It's a trap: The catalytic asymmetric carboannulation of alkylidene oxindole, coumarin, and malonate substrates with allylsilanes in the presence of a ScIII/BArF/indapybox catalyst affords functionalized cyclopentanes containing a quaternary carbon center with high stereoselectivity. Enantioselective allylation and asymmetric lactone formation by trapping of the β-silyl carbocation are also presented.
Unprotected vinyl aziridines: Facile synthesis and cascade transformations
Baktharaman, Sivaraj,Afagh, Nicholas,Vandersteen, Adelle,Yudin, Andrei K.
, p. 240 - 243 (2010)
(Figure presented) Functionalized vinylaziridines, readily available from water-stable aziridine aldehydes have led to the construction of a variety of stereochemically rich heterobicycles. A cascade ring-opening/ring-contraction mechanism operates In the course of the process. These results underscore the notion that Interesting and useful nitrogen-mediated relay processes can arise when elements of strain are merged with the manifolds of enamine/iminium ion reactivity.
Catalytic Asymmetric Synthesis of Cyclopentene-spirooxindoles Bearing Vinylsilanes Capable of Further Transformations
Cobo, Angel A.,Armstrong, Brittany M.,Fettinger, James C.,Franz, Annaliese K.
, p. 8196 - 8200 (2019)
We report a scandium-catalyzed [3 + 2] annulation of alkylideneoxindoles with allenylsilanes for the enantioselective formation of cyclopentene-spirooxindoles containing vinylsilanes. Using a Sc(OTf)2/PyBOX/BArF complex, the spiroannulation of allenylsilanes affords products with >94:6 dr and >90:10 er. The effect of the counterion and ligand to control selectivity is discussed. The transformation of the vinylsilane is demonstrated using cross-coupling, epoxidation, and Tamao-Fleming oxidation reactions. A series of competition experiments provide a comparison of nucleophilicity between allyl- and allenylsilanes.
Phosphonium-iodonim ylides in nucleophilic substitution reactions
Matveeva,Podrugina,Grishin,Pavlova,Zefirov
, p. 201 - 206 (2007)
Properties of mixed phosphonium-iodonium ylides were investigated, and the compounds were shown to be capable to behave as O-nucleophiles in nucleophilic substitution reactions.
Asymmetric Catalytic Diverse Ring Opening/Cycloadditions of Cyclobutenones with (E)-Alkenyloxindoles and (E)-Dioxopyrrolidines
Luo, Yao,Zhang, Hang,Wang, Siyuan,Zhou, Yuqiao,Dong, Shunxi,Feng, Xiaoming
, p. 2645 - 2650 (2020)
Highly enantioselective ring-opening/cycloaddition reactions of cyclobutenones were achieved by employing chiral N,N′-dioxide/metal complexes as the catalysts. The Diels-Alder type cycloaddition with (E)-alkenyloxindoles yielded spirocyclohexaneoxindoles with excellent results. Meanwhile, a hetero-Diels-Alder process occurred with (E)-dioxopyrrolidines to afford spiropyrrolidinone-dihydropyranone derivatives.
Mechanically induced solid-state generation of phosphorus ylides and the solvent-free wittig reaction
Balema, Viktor P.,Wiench, Jerzy W.,Pruski, Marek,Pecharsky, Vitalij K.
, p. 6244 - 6245 (2002)
We describe the nearly quantitative preparation of phosphorus ylides and the Wittig reaction occurring in the solid sate during high-energy mechanochemical processing. Initial insights into the details of the discovered chemical transformations indicate that high-energy mechanical processing supports the interaction of reacting centers by breaking crystallinity of the reactants and by providing mass transfer without a solvent. Copyright
Synthesis and Structure of Mixed Phosphonium-iodonium Ylide
Matveeva,Podrugina,Grishin,Tkachev,Zhdankin,Aldoshin,Zefirov
, p. 536 - 541 (2003)
A mixed phosphonium-iodonium ylide, phenyliodoniumethoxycarbonylmethylenetriphenyl-phosphorane borofluoride, was synthesized. Its structure was established by means of X-ray diffraction analysis. Temperature dependence of 1H, 13C, and 31P spectra of the ylide synthesized was investigated. A dynamic equilibrium between Z and E-isomers was observed.
Concentration-Dependent Main-Chain Dynamics of Sodium Polyacrylate As Probed by NMR in the Semidilute Regime
Rijn, C. J. M. van,Jesse, W.,Bleijser, J. de,Leyte, J. C.
, p. 203 - 210 (1987)
Sodium polyacrylate chains exhibit reduced reorientational mobility in the semidilute regime as probed by frequency-dependent nuclear magnetic relaxation experiments.Nuclear magnetic relaxation rates of deuterons have been measured in aqueous solutions of methylene-deuteriated poly(acrylic acid) (CD2-PAA).Upon diluting a neutralized solution of CD2-PAA (sodium polyacrylate), a sharp increase of the transverse relaxation rate R2 was observed, whereas the longitudinal relaxation rate R1 remained unaffected.It is shown that in the semidilute regime slow motions with correlation times > 1E-8 s show up irrespective of the fast (internal) motions with correlations times ca. 1E-9 s.The origin of these slow motions is indicated by polyelectrolyte theory; the large correlation times are probably due to the enhanced (electrostatic) stiffness of the CD2-PAA chain in the semidilute regime.In concordance with this idea is the fact that the large correlation times decrease when a simple salt (NaCl) is added to the solution.An implication for the interpretation of counterion relaxation is discussed.
Synthesis of 5,6-dehydrokawain and some fluorinated analogues
Obi, Grace,Van Heerden, Fanie R.
, p. 1482 - 1486 (2018)
An efficient methodology for the synthesis of 6-styrenylpyrone in a four-step sequence is reported. The reactions were performed under catalyst-free conditions with mild and affordable reagents to produce 5,6-dehydrokawain and fluorinated derivatives in good to excellent overall yields (72–86%) on a multigram scale. Two novel difluorinated derivatives are reported here for the first time.
