- Photocontrolled Cobalt Catalysis for Selective Hydroboration of α,β-Unsaturated Ketones
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Selectivity between 1,2 and 1,4 addition of a nucleophile to an α,β-unsaturated carbonyl compound has classically been modified by the addition of stoichiometric additives to the substrate or reagent to increase their “hard” or “soft” character. Here, we demonstrate a conceptually distinct approach that instead relies on controlling the coordination sphere of a catalyst with visible light. In this way, we bias the reaction down two divergent pathways, giving contrasting products in the catalytic hydroboration of α,β-unsaturated ketones. This includes direct access to previously elusive cyclic enolborates, via 1,4-selective hydroboration, providing a straightforward and stereoselective route to rare syn-aldol products in one-pot. DFT calculations and mechanistic experiments confirm two different mechanisms are operative, underpinning this unusual photocontrolled selectivity switch.
- Beltran, Frédéric,Bergamaschi, Enrico,Funes-Ardoiz, Ignacio,Teskey, Christopher J.
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p. 21176 - 21182
(2020/09/17)
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- Pd-catalyzed regioselective C?H alkenylation and alkynylation of allylic alcohols with the assistance of a bidentate phenanthroline auxiliary
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A Pd-catalyzed regioselective C?H alkenylation of allylic alcohols with electron-deficient alkenes has been developed. The key to success is the introduction of bidentately coordinating phenanthroline directing group, which enables the otherwise challenging and regioselective C?H activation at the proximal alkenyl C?H bonds over the conceivably competitive allylic C?O bond activation. The same Pd/phenanthroline system is efficient for the C?H alkynylation of allylic alcohols with alkynyl bromides.
- Hirano, Koji,Miura, Masahiro,Xu, Shibo
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supporting information
p. 9059 - 9064
(2020/12/02)
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- Hypervalent-iodine-mediated ring-contraction monofluorination affording monofluorinated five-membered ring-fused oxazolines
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The first ring-contraction monofluorination reaction mediated by a hypervalent iodine reagent is reported, and the use of the reaction for the synthesis of monofluorinated five-membered ring-fused oxazolines is described. By means of this reaction, a fluorine atom can be selectively introduced either on the five-membered ring or external to it, depending on whether or not the substrate has C-4 alkyl substituents. The reaction was used for the further conversion of probenecid and isoxepac.
- Han, Yong-Chao,Zhang, Yan-Dong,Jia, Qun,Cui, Jian,Zhang, Chi
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supporting information
p. 5300 - 5303
(2017/11/06)
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- Mechanistic Studies on a Cu-Catalyzed Asymmetric Allylic Alkylation with Cyclic Racemic Starting Materials
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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.
- Rideau, Emeline,You, Hengzhi,Sidera, Mireia,Claridge, Timothy D. W.,Fletcher, Stephen P.
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supporting information
p. 5614 - 5624
(2017/04/27)
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- HYDROGENATION OF ALDEHYDE OR KETONE COMPOUNDS WITH FE/TRIDENTATE LIGANDS COMPLEXES
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The present invention relates to the field of catalytic hydrogenation and, more particularly, to the use of Fe complexes with tridentate ligands, having one amino or imino coordinating group and two phosphino coordinating groups, in hydrogenation processes for the reduction of ketones or aldehydes, into the corresponding alcohol or diol, respectively.
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Page/Page column 25-27
(2017/01/02)
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- HYDROGENATION OF ESTERS WITH FE/TRIDENTATE LIGANDS COMPLEXES
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The present invention relates to the field of catalytic hydrogenation and, more particularly, to the use of Fe complexes with tridentate ligands, having one amino or imino coordinating group and two phosphino coordinating groups, in hydrogenation processes for the reduction of ketones, aldehydes, esters or lactones into the corresponding alcohol or diol, respectively.
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Page/Page column 17; 18
(2015/07/07)
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- SUBSTITUTED DIAMINOCARBOXAMIDE AND DIAMINOCARBONITRILE PYRIMIDINES, COMPOSITIONS THEREOF, AND METHODS OF TREATMENT THEREWITH
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Provided herein are Diaminopyrimidine Compounds having the following structures: wherein R1, R2, R3, and R4 are as defined herein, compositions comprising an effective amount of a Diaminopyrimidine Compound, and methods for treating or preventing liver fibrotic disorders or a condition treatable or preventable by inhibition of a JNK pathway.
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Page/Page column 154; 155
(2012/11/07)
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- Enzymatic resolution of racemic secondary cyclic allylic alcohols
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The resolutions of five racemic cyclic alcohols: 6,6-dimethylcyclohex-2-en-1-ol (±)-5, 4,4-dimethylcyclohex-2-en-1-ol (±)-7, 5,5-dimethylcyclohex-2-en-1-ol (±)-11 and isomeric trans-(±)-13 and cis-piperitols (±)-14 are presented. They were resolved by enzymatic esterification with vinyl esters or by enzymatic hydrolysis of their racemic esters in phosphate buffer. The following lipases were used as biocatalysts: Novozyme 435 (Candida antarctica), Amano PS (Burkholderia cepacia) and lipase from Candida cylindracea. All isomers of alcohols were obtained with at least 96% ee.
- Winska, Katarzyna,Grudniewska, Aleksandra,Chojnacka, Anna,Bialonska, Agata,Wawrzenczyk, Czeslaw
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experimental part
p. 670 - 678
(2010/08/07)
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- Generation of hafnium hydride and its application to chemo- and diastereoselective reactions
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Hafnium hydride was generated by the transmetalation between Bu 3SnH and HfCl4 using either THF or EtCN as the solvent. This process effectively reduced aldehydes, aldimines, ketones, and esters. In the hafnium hydride reduction of α-alkoxyketones, the diastereoselectivity was dependent on whether THF or EtCN was used as the solvent. Georg Thieme Verlag Stuttgart.
- Shibata, Ikuya,Miyamoto, Shinji,Itoh, Toru,Baba, Akio
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experimental part
p. 1495 - 1497
(2009/12/08)
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- Reduction of α,β-unsaturated ketones with diphenylsilanes bearing several substituents on their phenyl moiety catalyzed by rhodium-phosphine complexes
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1,4-Addition product was afforded exclusively by rhodiumphosphine complex-catalyzed hydrosilylation by using 2-cyclohexen-1-one and a dihydrosilane bearing an ether substituent in spite of the fact that dihydrosilanes were believed to give 1,2-addition product selectively. Copyright
- Imao, Daisuke,Hayama, Miyuki,Ishikawa, Kohta,Ohta, Tetsuo,Ito, Yoshihiko
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p. 366 - 367
(2007/10/03)
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- A radical cyclisation based cyclopentenone annulation of allyl alcohols
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A four-step cyclopentenone annulation reaction of allylic alcohols employing a 5-exo-trig radical cyclisation reaction of mixed allyl methyl ketals of bromoacetone as the key step is described. The annulated product 12b obtained from 2,3-dimethylcyclohexenol has been further elaborated into (±)-epibakkenolides employing a 5-exo-dig radical cylisation reaction based α-spiro-β-methylene-γ-butyrolactone annulation methodology.
- Srikrishna,Viswajanani,Sattigeri
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p. 2975 - 2983
(2007/10/03)
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- Reductions of α,β-unsaturated ketones by NaBH4 or NaBH4 + CoCl2: Selectivity control by water or by aqueous micellar solutions
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Operationally simple and environmentally benign procedures have been developed to selectively reduce different α,β-unsaturated ketones, 4,4- dimethylcyclohex-2-ene-1-one (1), isophorone (2), benzylideneacetone (3), chalcone (4) by NaBH4 or by the system NaBH4 + COCl2. Alternative reaction media to the extensively used MeOH have been explored, and new procedures take advantage of the acceleration and chemoselectivity induced by water or by aqueous micellar solutions. It was possible to selectively and quantitatively afford pure products of 1,2 and of 1,4 reduction as well as the totally reduced compounds (yield and selectivity > 90%) by simple changes in the experimental conditions.
- Aramini, Andrea,Brinchi, Lucia,Germani, Raimondo,Savelli, Gianfranco
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p. 1793 - 1797
(2007/10/03)
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- Asymmetric hydrogenation of cyclic α,β-unsaturated ketones to chiral allylic alcohols
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The Ru(II)-BINAP-1,2-diphenylethylenediamine combined catalyst system effects asymmetric hydrogenation of certain cyclic enones in 2-propanol containing KOH with a substrate/catalyst molar ratio of 250 to 2500. The hydrogenation occurs selectively at the C=O function with excellent enantio- or diastereoselectivity.
- Ohkuma, Takeshi,Ikehira, Hideyuki,Ikariya, Takao,Noyori, Ryoji
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p. 467 - 468
(2007/10/03)
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- Reductive cleavage of benzyl ethers with lithium naphthalenide. A convenient method for debenzylation
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An operationally simple, high-yielding and highly chemoselective procedure has been developed for the conversion of benzyl ethers to the corresponding alcohols, using lithium naphlhalenide as the reagent.
- Liu, Hsing-Jang,Yip, Judy,Shia, Kak-Shan
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p. 2253 - 2256
(2007/10/03)
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- Lanthanide complexes in organic synthesis: Selective NaBH4 reduction of α,β-unsaturated carbonyl compounds
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The anhydrous lanthanide(III) complexes of N, N'-ethylene-bis(2-aminobenzamide) and N,N'-propylene-bis (2-aminobenzamide) catalyze the sodium borohydride reduction of α, β-unsaturated carbonyl compounds very selectively under ambient conditions. The heavier lanthanide complexes give good yields as compared to their hydrated chloride salts.
- Swamy, S. Jagannatha,Kumar, B. Kishore
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p. 484 - 486
(2007/10/03)
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- THE INFLUENCE OF LITHIUM COMPLEXING AGENTS ON THE REGIOSELECTIVITY OF REDUCTIONS OF SUBSTITUTED 2-CYCLOHEXENONES BY LiAlH4 and LiBH4
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A reversal of regioselectivity of LiAlH4 or LiBH4 reduction of 2-cyclohexenone induced by addition of -cryptand to the reaction medium is accompanied by a rate decrease.In the absence of the cryptand, carbonyl attack predominates (C1:C3=86:14 with LiAlH4 in THF).In the presence of the cryptand, double bond attack is favoured (C1:C3=14:86).This effect is larger with LiAlH4 than with LiBH4.This trend is general in the case of five substituted 2-cyclohexenones.Using 12-crown-4 as a Li+ coordinator, a change in regioselectivity occurs but it is less pronunced than with the cryptand.
- Loupy, Andre,Seyden-Penne, Jacqueline
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p. 1937 - 1942
(2007/10/02)
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