- Gold-Catalyzed Synthesis of Chiral Cyclopentadienyl Esters via Chirality Transfer
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Efficient access to chiral cyclopentadienyl esters from readily accessible chiral enynyl ester substrates is developed. Typically high levels of chirality transfer realized in this homogeneous gold catalysis are attributed to the intermediacy of a chiral bent allene gold complex. Cyclopentadienyl esters can be prepared in good yields and with excellent enantiomeric excesses. The synthetic utilities of the chiral cyclopentadienyl esters are demonstrated by the Diels-Alder reactions, fluorination, alkylation, and epoxidation without any notable erosion of enantiopurity.
- Zhao, Ke,Hsu, Yu-Chen,Yang, Ziguang,Liu, Rai-Shung,Zhang, Liming
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- Enantioselective Cyanosilylation of Alkynyl Ketones Catalyzed by Combined Systems Consisting of Chiral Ruthenium(II) Complex and Lithium Phenoxide
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Asymmetric cyanosilylation of alkynyl ketones with the catalyst systems consisting of amino acid/2,2′-bis(diphenylphosphino)-1,1′-binaphthyl (BINAP)/ruthenium(II) complex and lithium phenoxide (Ru?Li cat.) was studied. The reaction was conducted in tert-butyl methyl ether (TBME) at ?78 °C with a substrate-to-catalyst molar ratio (S/C) as high as 2000. A series of simple and functionalized ketones was converted into the alkynyl tertiary cyanohydrin derivatives in up to 99% ee. Appropriate selection of an amino-acid ligand of the catalyst according to the substrate structure was crucially important to achieve high enantioselectivity and a wide scope of substrates. Transformation of the chiral cyanohydrin product into a functionalized lactone was also examined. (Figure presented.).
- Ohkuma, Takeshi,Kurono, Nobuhito,Sakaguchi, Yusuke,Yamauchi, Kohei,Yurino, Taiga
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supporting information
p. 1517 - 1522
(2018/02/28)
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- Direct synthesis of pyrazoles from esters using tert-butoxide-assisted C-(C=O) coupling
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This paper describes the direct synthesis of pyrazoles from esters that comprises two sequential reactions: tert-butoxide-assisted C-C(=O) coupling reaction to yield β-ketonitrile or α,β-alkynone intermediates, and condensation by hydrazine addition. The method reported allows for easy control of the regioselectivity and structure of substituents at N-1, C-3, C-4 and/or C-5 positions.
- Kim, Bo Ram,Sung, Gi Hyeon,Ryu, Ki Eun,Lee, Sang-Gyeong,Yoon, Hyo Jae,Shin, Dong-Soo,Yoon, Yong-Jin
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supporting information
p. 9201 - 9204
(2015/06/08)
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- Synthesis of β-ketonitriles, α,β-alkynones and biscabinols from esters using tert-butoxide-assisted C(=O)-C (i.e., acyl-C) coupling under ambient conditions
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We demonstrated the synthesis of β-ketonitriles, α,β- alkynones, and biscarbinols using tert-butoxide-assisted C(CO)-C (i.e., acyl-C) coupling of esters under ambient conditions. tert-Butoxide-assisted C(CO)-C (i.e., acyl-C) coupling of esters with cyanomethylenes and acetylenes under transition metal-free ambient conditions gives β-ketonitriles, α,β-alkynones and/or aryl bis(phenylethynyl)carbinols in moderate-to-good yields. It is noteworthy that this is a rapid, facile, and efficient process under ambient conditions, and use of cheap and stable starting materials.
- Kim, Bo Ram,Lee, Hyung-Geun,Kang, Seung-Beom,Jung, Kwang-Ju,Sung, Gi Hyeon,Kim, Jeum-Jong,Lee, Sang-Gyeong,Yoon, Yong-Jin
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p. 10331 - 10336
(2013/11/19)
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- Efficient methods for the preparation of acetylenic ketones
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A number of acetylenic ketones RCCC(=O)R' have been obtained in good yields from lithiated acetylenes RCCLi and acetic anhydride, N,N-dimethylacetamide, or N,N-dimethylbenzamide.The most convenient and general method consists of treating alkynylzinc chlorides with acid halides R'C(=O)Cl.Benzoyl chloride (R'=Ph), acryloyl chloride (R'=CH2=CH) and butynoyl chloride (R'=C2H5CC) react only in the presence of a catalytic amount of Pd4.
- Verkruijsse, H. D.,Heus-Kloos, Y. A.,Brandsma, I.
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p. 289 - 294
(2007/10/02)
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- Hydration of Diacetylene Compounds. Synthesis of a Marine Natural Product: (+/-)-1-(2,6,6-Trimethyl-4-hydroxycyclohexenyl)-1,3-butanedione
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The marine natural product (+/-)-1-(2,6,6-trimethyl-4-hydroxycyclohexenyl)-1,3-butanedione (1) was synthesized from known the keto alcohol 3 and 1,4-dichlorobut-2-yne.The synthetic sequence involves dehydration of the diyne tertiary alcohol 2 and hydratio
- Constantino, Mauricio G.,Donate, Paulo M.,Petragnani, Nicola
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p. 387 - 390
(2007/10/02)
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- Acetylenic retinals form functional bacteriorhodopsins but do not form bovine rhodopsins
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Three acetylenic retinals bearing a triple bond between the carbon atoms 7 and 8, and carrying no, two, or three methyl groups on the cyclohexene ring, were synthesized and various isomers obtained by illumination and subsequent chromatographic separation. The introduction of the acetylenic bond leads to a different geometrical arrangement of the cyclohexene ring with respect to the polyene side chain. Attempts to reconstitute rhodopsins and isorhodopsins with any of these compounds failed. Bacteriorhodopsins formed with the 13-cis and the all-trans isomers of all three acetylenic retinals showing absorption maxima between 490 and 530 nm. The increasing number of methyl groups on the ring correlated with an increasing red shift of the absorption maximum of the chromoproteins. This same correlation was found for the proton-pumping activity of the acetylenic bacteriorhodopsins. The results are in agreement with the fact that in rhodopsin a covalent binding at the carbonyl group (Schiff's base formation) and also a fixation at the cyclohexene ring of retinal occurs. The changed geometry of the acetylenic retinals, therefore, prevents binding. In bacteriorhodopsin, which lacks a specific cyclohexene ring binding site, the acetylenic retinals form active molecules. However, the contribution of the ring and its substituents to the function of bacteriorhodopsin is significant.
- Gartner,Oesterhelt,Seifer-Schiller,et al.
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p. 5654 - 5659
(2007/10/02)
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