- (Z)-3-alkylidene-4,5-dihydro-4-hydroxy-5-methyl-2-(3H)-furanones by regio- and diastereoselective ene reaction of singlet oxygen (Schenk reaction) with γ-hydroxy vinylstannanes: An enantioselective synthesis of dihydromahubanolide B
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(Z)-3-Alkylidene-4,5-dihydro-4-hydroxy-5-methyl-2-(3H)-furanones 5 were prepared from appropriately substituted propargylic alcohols 1 by a sequence of hydromagnesation to γ-hydroxy vinylstannanes 2, subsequent photooxygenation and reduction to stannyl diols 3, iododestannylation to iodo diols 4, and finally cyclization by palladium-catalyzed carbonylation (for 5a) or Ni(CO)2(PPh3)2 (for 5b,c). The reaction sequence can be performed enantioselectively by starting with chiral propargylic alcohols. The current approach constitutes a convenient four-step synthesis of optically active lactones 5 from readily available starting materials and is applied herein to the preparation of the natural lactone dihydromahubanolide B.
- Adam,Klug
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- Phosphine-Catalyzed Intermolecular Annulations of Fluorinated ortho-Aminophenones with Alkynones – The Switchable [4+2] or [4+2]/[3+2] Cycloaddition
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A phosphine-catalyzed intermolecular annulation reaction of functionalized ortho-aminoacetophenones with alkynones has been disclosed in this paper. A variety of 2-alkynylquinolines and benzo-fused indolizine were selectively afforded in moderate to good yields at different reaction temperatures and with different phosphine catalysts via the in situ generated zwitterionic intermediate derived from alkynone and phosphine. (Figure presented.).
- Zhang, Yanshun,Sun, Yaoliang,Wei, Yin,Shi, Min
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supporting information
p. 2129 - 2135
(2019/03/13)
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- Synthesis of Vinyl-, Allyl-, and 2-Boryl Allylboronates via a Highly Selective Copper-Catalyzed Borylation of Propargylic Alcohols
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An efficient methodology for the synthesis of vinyl-, allyl-, and (E)-2-boryl allylboronates from propargylic alcohols via Cu-catalyzed borylation under mild conditions is reported. In the presence of commercially available Cu(OAc)2 or Cu(acac)2 and Xantphos, the reaction affords the desired products in up to 92% yield with a broad substrate scope (43 examples). Isolation of an allenyl boronate as the reaction intermediate suggests that an insertion-elimination-type reaction, followed by borylcupration, is involved in the borylation of propargylic alcohols.
- Mao, Lujia,Bertermann, Rüdiger,Emmert, Katharina,Szabó, Kálmán J.,Marder, Todd B.
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supporting information
p. 6586 - 6589
(2017/12/26)
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- In situ generation of nucleophilic allenes by the gold-catalyzed rearrangement of propargylic esters for the highly diastereoselective formation of intermolecular C(sp3)-C(sp2) bonds
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New perspectives, in particular for the synthesis of isochromane derivatives (see scheme), are provided by the title reaction. Excellent diastereoselectivites are achieved in this reaction which proceeds through a gold-catalyzed 1,3-acyloxy migration. In some cases exclusively the Z isomer is detected. Copyright
- Yu, Yang,Yang, Weibo,Rominger, Frank,Hashmi, A. Stephen K.
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supporting information
p. 7586 - 7589
(2013/07/26)
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- The substrate spectrum of the inverting sec-alkylsulfatase Pisa1
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The substrate spectrum of the inverting alkylsulfatase Pisa1 was investigated using a range of sec-alkyl sulfate esters bearing aromatic, olefinic and acetylenic moieties. Perfect enantioselectivities were obtained for substrates bearing groups of different size adjacent to the sulfate ester moiety. Insufficient selectivities could be doubled by using dimethyl sulfoxide (DMSO) as co-solvent. Hydrolytically unstable benzylic sulfate esters could be sufficiently stabilised by introduction of electron-withdrawing substituents. Overall, Pisa1 appears to be a very useful inverting alkylsulfatase for the deracemisation of rac-sec-alcohols via enzymatic hydrolysis of their corresponding sulfate esters, which furnishes homochiral products possessing the 'anti-Kazlauskas' configuration. Copyright
- Schober, Markus,Knaus, Tanja,Toesch, Michael,MacHeroux, Peter,Wagner, Ulrike,Faber, Kurt
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p. 1737 - 1742
(2012/07/31)
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- Synthesis of novel 2H,5H-dihydrofuran-3-yl ketones via ISNC reactions
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Unique 1-[2H,5H-dihydrofur-3-yl]ketones have been synthesized from propargylic nitroethers via intramolecular cycloadditions involving silyl nitronates. Various substituent groups were placed on the 2 and 5 positions of the dihydrofuran rings. We examined the scope of the long-range coupling in proton NMR of the oxo-dihydrofuran products. The identities of the diastereomers resulting from the Michael addition/cycloaddition reactions were tentatively assigned for the first time. CAChe MNDO PM5 and CONFLEX programs were engaged to assist with the identification of these stereoisomers. The reaction times and conditions for these oxo-dihydrofurans were found to be different than that of the published dihydrofuranals, which led us to propose a different mechanism.
- Grandbois, Matthew L.,Betsch, Kelsie J.,Buchanan, William D.,Duffy-Matzner, Jetty L.
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supporting information; scheme or table
p. 6446 - 6449
(2011/02/23)
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- Nickel-catalyzed asymmetric cross-couplings of racemic propargylic halides with arylzinc reagents
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A stereoconvergent method for the catalytic asymmetric Negishi cross-coupling of racemic secondary propargylic halides with arylzinc reagents has been developed. Neither family of compounds has previously been shown to be a suitable partner in such coupling processes. From a practical point of view, it is noteworthy that the catalyst components (NiCl2·glyme and pybox ligand 1) are commercially available. Copyright
- Smith, Sean W.,Fu, Gregory C.
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supporting information; experimental part
p. 12645 - 12647
(2009/05/09)
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- Adducts of thianthrene- and phenoxathiin cation radical salts with symmetrical alkynes. Structure and formation of cumulenes on alumina leading to α-diketones, α-hydroxyalkynes, and α-acetamidoalkynes
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Thianthrene cation radical tetrafluoroborate (Th.+BF 4-) added to 2-butyne, 3-hexyne, 4-octyne, and 5-decyne in MeCN to form trans bisadducts E(Th+)C=C(Th+)R, where E = Me, Et, Pr, Bu (7a-d). Phenoxathiin cation radical tetrafluoroborate (PO .+BF4-) added similarly to the last three alkynes to form adducts E(PO+)C=C(PO+)E, 8b-d. Cyclic monoadducts were not found. The trans structures of 7 and 8 were deduced with X-ray crystallography (7c) and NME spectroscopy. When solutions of adducts in CHCl3 and MeCN were deposited on activated alumina, elimination of thianthrene (Th) and phenoxathiin (PO) occurred almost quantitatively. Detailed studies with (7b-d) indicated that a cumulene (15) was formed by the elimination of Th and that 15 was subsequently converted into small amounts of other products. In CHCl3, these products were the respective alkyne, thianthrene 5-oxide, an α-diketone (11), an α-hydroxyalkyne (12), and hydrogen. The same products were formed in MeCN along with an α-acetamidoalkyne (13). The formation of 15 and products derived from it is explained and was confirmed by preparation and reactions of 2,3,4-hexatriene.
- Shine, Henry J.,Rangappa, Paramashivappa,Marx, John N.,Shelly, Dennis C.,Ould-Ely, Teyeb,Whitmire, Kenton H.
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p. 3877 - 3883
(2007/10/03)
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- The effect of catechin derivatives on the enantioselectivity of lipase-catalyzed hydrolyses of alkynol benzoate esters
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Polyphenols, such as (+)-catechin and pyrogallol could be used to enhance stereochemical control in the lipase-catalyzed hydrolysis of alkynol benzoate esters, leading to increased enantioselectivities in the kinetic resolution of alkynols with lipase Amano AH.
- Nakamura, Kaoru,Takenaka, Keishi
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p. 415 - 422
(2007/10/03)
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- Enantioselective reduction of prochiral ketones by catecholborane catalysed by chiral group 13 complexes
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LiGaH4, in combination with the S,O-chelate 2-hydroxy-2′-mercapto-1,1′-binaphthyl (MTBH2), forms an active catalyst for the asymmetric reduction of prochiral ketones, with catecholborane as the hydride source. Enantioface differentiation is on the basis of the steric requirements of the ketone substituents. Aryl/ n-alkyl ketones are reduced in 90-93% ee and RC(O)Me (e.g. R = iPr, cycloC6H11, tBu) in 60-72% ee. Other borane sources and alternative catalyst structures based on indium do not form enantioselective catalysts.
- Blake, Alexander J.,Cunningham, Anthony,Ford, Alan,Teat, Simon J.,Woodward, Simon
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p. 3586 - 3594
(2007/10/03)
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- Catalytic enantioselective reduction of ketones by a chiral gallium complex and catecholborane
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A catalytically active version of Noyori's famous BINAL reagent Li[A1H(OEt)-(BINOL dianion)] is formed by the combination of LiGaH4, monothiobinaphthol (MTB), and catecholborane. With this mixture unsymmetrical ketones can be reduced in high enantioselectively. Un = unsaturated unit; R = alkyl.
- Ford, Alan,Woodward, Simon
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p. 335 - 336
(2007/10/03)
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- PalladiumdD-catalyzed exchange and isomerization reactions. 17. Exchange of chiral allyl alcohols with hydroxide, methoxide, and phenyl at high [Cl-]. Stereochemistry of the wacker reaction
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At high [Cl ] (> 2.0 M), PdCl42- catalyzes the exchange of chiral allylic alcohols with hydroxy, methoxy, and phenyl to give chiral allyl-substituted olefins. With unsymmetrical olefins, isomerization occurs along with exchange. The hydroxyl exchange occurs in aqueous solution while the other exchanges are carried out in methanol solution. At low [Cl-] (0.1 M) oxidation to the corresponding β-hydroxy-, methoxy-, and phenyl-substituted carbonyl compounds occurred. The absolute configurations of the oxidation and exchange products should be the same if the same mode of addition to the Pd(II)-β-complex is operative. The absolute configurations of the oxidation and exchange products for the phenylation reaction were the same, while for hydroxy and methoxy they were different. This result indicates methanol and water must have different stereochemistries of addition at high and low [Cl-]. Thus, previous studies showing anti hydroxypalladation at high [Cl-] are not valid indicators of the stereochemistry at low [Cl-]. If anti addition occurs at high [Cl-], the addition must be syn at low [Cl-].
- Hamed, Othman,Henry, Patrick M.,Thompson, Charles
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p. 7745 - 7750
(2007/10/03)
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- Oxygenation of alkynes to α,β-acetylenic ketones with dioxygen catalyzed by N-hydroxyphthalimide combined with a transition metal
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Alkynes were successfully converted into α,β-acetylenic carbonyl compounds through radical-catalyzed aerobic oxidation using N-hydroxyphthalimide (NHPI) combined with a transion metal under mild conditions.
- Sakaguchi, Satoshi,Takase, Tomoyuki,Iwahama, Takahiro,Ishii, Yasutaka
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p. 2037 - 2038
(2007/10/03)
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- Selective Reductions. 46. Effect of the Steric Requirement at the 2-Position of Apopinene on chiral Reductions. B-(Iso-2-ethylapopinocampheyl)- and B-(Iso-2-n-propylapopinocampheyl)-9-borabicyclononanes as Improved Reagents for the Chiral Reduction of α,β-Acetylenic Ketones ...
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B-(Iso-2-ethylapopinocampheyl)-9-borabicyclononane (Eapine-Borane, 7), and B-(Iso-2-n-propylapopinocampheyl)-9-borabicyclononane (Prapine-Borane, 9), prepared via the hydroboration of 2-ethylapopinene (6) or 2-n-propylapopinene (8), respectively, with 9-borabicyclononane, reduce prochiral α,β-acetylenic ketones and α-keto esters to the corresponding alcohols with significantly higher optical induction than does Alpine-Borane (1). (-)-2-n-Propylapopinene was synthesized by treating nopyl tosylate with dimethyl cuprate prepared in situ from methyllithium and cuprous iodide. (+)-2-n-Propylapopinene was synthesized by Schlosser metalation of (+)-α-pinene followed by treatment with ethyl iodide. 4-Phenyl-3-butyne-2-one was reduced to the corresponding propargylic alcohol in 89percent ee and 96percent ee by Eapine-Borane and Prapine-Borane, respectively, as compared to 82percent ee with Alpine-Borane.Similar improved results were realized in the reduction of other acetylenic ketones by Eapine-Borane and Prapine-Borane.Similar improvements in the optical yields were realized in the reduction of α-keto esters by Eapine-Borane.For example, while Alpine-Borane produced methyl and ethyl lactate in 92percent and 91percent ee, respectively, Eapine-Borane gave these alcohols in 97percent and 96percent ee, respectively.Unfortunately, Prapine-Borane shows no improvement in percent ee for the reduction of α-keto esters.The increase in the percent ee realized is tentatively attributed to the increased steric requirements of the alkyl group at the 2-position of apopinene.
- Brown, Herbert C.,Ramachandran, P. Veeraraghavan,Weissman, Steven A.,Swaminathan, S.
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p. 6328 - 6333
(2007/10/02)
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- Stereochemistry of Olefin and Fatty Acid Oxidation. Part 1. Autooxidation of Hexene and Hepta-2,5-diene Isomers
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The stereochemistry of the autooxidation of hex-1-ene, cis- and trans-hex-2-ene, cis- and trans-hex-3-ene, and of the three geometrical isomers of hepta-2,5-diene, has been determined by the reduction of the hydroperoxides produced and analysis of the resulting allylic alcohols.The relative proportions of the isomeric hydroperoxides are explicable in termes of the conformation of the parent olefins which are capable of giving delocalised radicals on hydrogen abstraction.
- Frankel, Edwin N.,Garwood, Robert F.,Vinson, John R.,Weedon, Basil C. L.
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p. 2707 - 2714
(2007/10/02)
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