- Mechanistic Study and Development of Catalytic Reactions of Sm(II)
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Samarium diiodide (SmI2) is one of the most widely used single-electron reductants available to organic chemists because it is effective in reducing and coupling a wide range of functional groups. Despite the broad utility and application of SmI2 in synthesis, the reagent is used in stoichiometric amounts and has a high molecular weight, resulting in a large amount of material being used for reactions requiring one or more equivalents of electrons. Although few approaches to develop catalytic reactions have been designed, they are not widely used or require specialized conditions. As a consequence, general solutions to develop catalytic reactions of Sm(II) remain elusive. Herein, we report mechanistic studies on catalytic reactions of Sm(II) employing a terminal magnesium reductant and trimethylsilyl chloride in concert with a noncoordinating proton donor source. Reactions using this approach permitted reductions with as little as 1 mol % Sm. Mechanistic studies provide strong evidence that during the reaction, SmI2 transforms into SmCl2, therefore broadening the scope of accessible reactions. Furthermore, this mechanistic approach enabled catalysis employing HMPA as a ligand, facilitating the development of catalytic Sm(II) 5-exo-trig ketyl olefin cyclization reactions. The initial work described herein will enable further development of both useful and user-friendly catalytic reactions, a long-standing, but elusive goal in Sm(II) chemistry.
- Maity, Sandeepan,Flowers, Robert A.
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supporting information
p. 3207 - 3216
(2019/02/19)
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- The asymmetric alkylation of dimethylhydrazones; Intermolecular chirality transfer using sparteine as chiral ligand
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The asymmetric alkylation of ketones represents a fundamental transformation in organic chemistry. Chiral auxiliaries have been used almost exclusively for this transformation. Herein we describe a strategy for the generation of enantiomerically enriched α-alkylated ketones up to an er of 83:17, using a chiral ligand protocol. This journal is
- McSweeney, Christina M.,Foley, Vera M.,McGlacken, Gerard P.
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supporting information
p. 14817 - 14819
(2014/12/11)
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- Mechanistic study of samarium diiodide-HMPA initiated 5-exo-trig ketyl-olefin coupling: The role of HMPA in post-electron transfer steps
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The mechanistic importance of HMPA and proton donors (methanol, 2-methyl-2-propanol, and 2,2,2-trifluoroethanol) on SmI2-initiated 5-exo-trig ketyl-olefin cyclizations has been examined using stopped-flow spectrophotometric studies. In the pres
- Sadasivam, Dhandapani V.,Sudhadevi Antharjanam,Prasad, Edamana,Flowers II, Robert A.
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p. 7228 - 7229
(2008/12/21)
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- Complexes of cyclic polyaza chelators with cations of alkaline earth metals for enhanced biological activity
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Cyclic polyaza chelators that possess high affinity and specificity for first transition series metal cations exhibit an unanticipated improvement in biological activity when administered as complexes with cations of the alkaline earth metals, Ca(II) and Mg(II), most notably Ca(II). By virtue of this improvement, these complexes are particularly effective in the treatment of pathological conditions, including ischemia and ischemia-reperfusion injury.
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Page/Page column 11
(2010/02/11)
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- Identification and assignment of the absolute configuration of biologically active methyl-branched ketones from limnephilid caddis flies
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Glands of the 4th and 5th abdominal stemite of the caddis flies Potamophylax latipennis, Potamophylax cingulatus, and Glyphotaelius pellucidus contain (S)-4-methyl-3-heptanone (4a), (4S,6S)-4,6-dimethyl-3-octanone (4b), and (4S,6S)-4,6-dimethyl-3-nonanone (4c). As shown by gas chromatography coupled with electrophysiological recordings, these ketones elicit a strong response in the insects' antennae. The structural assignment of the compounds was achieved on the basis of mass spectra, enantioselective synthesis, and gas chromatography on a chiral stationary phase.
- Bergmann, Jan,Loefstedt, Christer,Ivanov, Vladimir D.,Francke, Wittko
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p. 3175 - 3179
(2007/10/03)
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- Regio-, Diastereo-, and Enantioselective Synthesis of vic-Diols via α-Silyl Ketones According to the SAMP/RAMP Hydrazone Method
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α-Silylated ketones 5 or 10 of high enantiomeric purity (ee>=90percent) are easily available by silylation or silylation/alkylation of ketones 1 or 6, resp., according to the SAMP/RAMP hydrazone method.Reduction of 5 or 10 with L-selectride, followed by oxidative cleavage of the C-Si bond, leads to vic-diols 11-13 with high diastereoselectivity (de>=90percent) and without racemization.The stereoselectivity of the reduction depends on the structure of the α-silyl ketones 5 or 10, the reducing reagents, and the solvents used.Key Words: Ketones, α-silyl / vic-Diols, diastereo- and enantioselective synthesis / SAMP/RAMP Hydrazones / L-Selectride reductions
- Enders, Dieter,Nakai, Shiro
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p. 219 - 226
(2007/10/02)
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- A Three-Step Pyridoannelation of Carbonyl Compounds
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The elaboration of a pyridine nucleus onto an α-methylene carbonyl compound can be accomplished through a three step reaction sequence based on the regiospecific alkylation of N,N-dimethylhydrazones with bromoethyl-1,3-dioxolane.Scope and limitations of the new method are considered.
- Marchetti, Mauro
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p. 1761 - 1765
(2007/10/02)
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- ASYMMETRIC SYNTHESES VIA METALATED CHIRAL HYDRAZONESOVERALL ENANTIOSELECTIVE α-ALKYLATION OF ACYCLIC KETONES
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A general method is described, which allows the overall enantioselective α-alkylation of acyclic ketones in good overall yields (44-86percent, 4 steps) and enantioselectivities ranging routinely from >94percent ee up to virtually complete asymmetric induction (99.5percent ee).The acyclic ketones are transformed to their corresponding "SAMP-hydrazones" (S)-2 by reaction with the enantiomerically pure hydrazine (S)-1-amino-2-methoxymethyl-pyrrolidine , readily available from (S)-proline.Metalation to form chiral azaenolates (S)-3 of ECCZCN-configuration and then alkylation to product hydrazones 4, followed by hydrazone cleavage via acidic hydrolysis of methiodides 9 in a two phase system or ozonolysis, leads to α-substituted, enantiomerically enriched, acyclic ketones 5.In special cases, where a phenyl group is directly attached to the newly generated center of chirality (5n,o,p), only low enantiomeric excesses are observed. 17 Examples, including first applications in natural product synthesis (cf 5a,b,e, and h) are summarized.
- Enders, D.,Eichenauer, H.,Baus, U.,Schubert, H.,Kremer, K. A. M.
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p. 1345 - 1359
(2007/10/02)
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