- Photoredox-Catalyzed Isomerization of Highly Substituted Allylic Alcohols by C?H Bond Activation
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Photoredox-catalyzed isomerization of γ-carbonyl-substituted allylic alcohols to their corresponding carbonyl compounds was achieved for the first time by C?H bond activation. This catalytic redox-neutral process resulted in the synthesis of 1,4-dicarbonyl compounds. Notably, allylic alcohols bearing tetrasubstituted olefins can also be transformed into their corresponding carbonyl compounds. Density functional theory calculations show that the carbonyl group at the γ-position of allylic alcohols are beneficial to the formation of their corresponding allylic alcohol radicals with high vertical electron affinity, which contributes to the completion of the photoredox catalytic cycle.
- Guo, Kai,Huang, Jun,Li, Anding,Li, Yuanhe,Yang, Zhen,Zhang, Zhongchao
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supporting information
p. 11660 - 11668
(2020/05/25)
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- Guiding a divergent reaction by photochemical control: Bichromatic selective access to levulinates and butenolides
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Allylic and acrylic substrates may be efficiently transformed by a sequential bichromatic photochemical process into derivatives of levulinates or butenolides with high selectivity when phenanthrene is used as a regulator. Thus, UV-A photoinduced cross-metathesis (CM) couples the acrylic and allylic counterparts and subsequent UV-C irradiation initiates E-Z isomerization of the carbon-carbon double bond, followed by one of two competing processes; namely, cyclization by transesterification or a 1,5-H shift and tautomerization. Quantum chemical calculations demonstrate that intermediates are strongly blue-shifted for the cyclization while red-shifted for the 1,5-H shift reaction. Hence, delaying the double bond migration by employing UV-C absorbing phenanthrene, results in a selective novel divergent all-photochemical pathway for the synthesis of fundamental structural motifs of ubiquitous natural products.
- Sutar, Revannath L.,Sen, Saumik,Eivgi, Or,Segalovich, Gal,Schapiro, Igor,Reany, Ofer,Lemcoff, N. Gabriel
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p. 1368 - 1374
(2018/02/09)
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- Mg(OMe)2 promoted allylic isomerization of γ-hydroxy-α,β-alkenoic esters to synthesize γ-ketone esters
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This work concerns the Mg(OMe)2 promoted allylic isomerization of γ-hydroxy-α,β-alkenoic esters with TMEDA as an additive. The isomerization proceeded under mild conditions and afforded γ-keto esters in high yield (up to 96%) within 2 h. Both (Z)- and (E)-γ-hydroxy-α,β-alkenoic esters were tolerated under the reaction conditions. This transformation involves the in situ formation of a dienolate intermediate from the easily accessible γ-hydroxy-α,β-alkenoic ester. The in situ generated dienolate can react with benzaldehyde and undergo a practical, useful tandem allylic isomerization-Aldol reaction to afford more functionalized compounds.
- Lai, Luhao,Li, A-Ni,Zhou, Jiawei,Guo, Yarong,Lin, Li,Chen, Wei,Wang, Rui
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supporting information
p. 2185 - 2190
(2017/03/17)
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- Cross metathesis of allyl alcohols: How to suppress and how to promote double bond isomerization
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Under standard conditions the cross metathesis of allyl alcohols and methyl acrylate is accompanied by the formation of ketones, resulting from uncontrolled and undesired double bond isomerization. By conducting the CM in the presence of phenol, the catalyst loading and the reaction time required for quantiative conversion can be reduced, and isomerization can be suppressed. On the other hand, consecutive isomerization can be deliberately promoted by evaporating excess methyl acrylate after completing cross metathesis and by adding a base or silane as chemical triggers.
- Schmidt, Bernd,Hauke, Sylvia
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p. 4194 - 4206
(2013/07/05)
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- Nucleophilic ring-opening of epoxide and aziridine acetates for the stereodivergent synthesis of β-Hydroxy and β-Amino γ-Lactams
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A highly regio- and stereoselective synthesis of novel β,γ- disubstituted γ-lactams with either an anti or syn relative configuration was developed from readily available epoxide and aziridine acetates. The key steps include the regio- and diastereocontrolled nucleophilic ring-opening of these three-membered heterocycles followed by mild reductive cyclization of the γ-azido ester intermediate. The method was also extended to an asymmetric synthesis of (4R,5S)-4-hydroxy-5-phenylpyrrolidin-2-one from a chiral epoxide acetate. The main features of this versatile synthesis of functionalized γ-lactams include the involvement of inexpensive reagents and mild conditions together with high chemical efficiency.
- Bisol, Tula B.,Bortoluzzi, Adailton J.,Sa, Marcus M.
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scheme or table
p. 948 - 962
(2011/04/12)
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- γ-oxygenation of α,β-unsaturated esters by vinylogous O-nitroso mukaiyama aldol reaction
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A practical procedure has been developed for γ-oxygenation of α,β-unsaturated esters by a vinylogous O-nitroso Mukaiyama aldol reaction followed by a one-pot N-O bond heterolysis of the in situ generated γ-aminoxy-α,β-unsaturated esters.
- Tian, Guo-Qiang,Yang, Jiong,Rosa-Perez, Kellymar
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supporting information; experimental part
p. 5072 - 5074
(2010/12/25)
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- Electrochemical generation and catalytic use of selenium electrophiles
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The generation and use of selenium electrophiles in catalytic, electrochemically driven selenenylation-elimination sequences is described. Georg Thieme Verlag Stuttgart.
- Niyomura, Osamu,Cox, Matthew,Wirth, Thomas
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p. 251 - 254
(2007/10/03)
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- Trans-selective conversions of γ-hydroxy-α,β-alkynoic esters to γ-hydroxy-α,β-alkenoic esters
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Matrix presented. γ-Hydroxy-α,β-acetylenic esters are used as precursors to prepare γ-hydroxy-α,β-alkenoic esters by means of trans-selective additions of two hydrogen atoms or one hydrogen atom and one iodine atom across the triple bonds. These methods a
- Meta, Christopher T.,Koide, Kazunori
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p. 1785 - 1787
(2007/10/03)
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- A general method for the preparation of 2,3,5-trisubstituted-furo[3,2-b]pyridines
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The preparation of 2,3,5-trisubstituted-furo[3,2-b]pyridines via a Pd(0)-catalyzed intramolecular cyclization of methyl 4-(6-chloro-2-iodopyridin-3-yloxy)-substituted-butenoates 9a-f is described. This approach was both efficient and general, and provided the highly functionalized heterocyclic ring system in high yield. Among the several examples provided is the preparation of 3-[2-(N,N-dimethylamino)ethyl]-5-(4-fluorobenzoyl)amino-2-methylfuro[3,2-b] pyridine 4, a selective 5-HT1F receptor agonist.
- Mathes, Brian M.,Filla, Sandra A.
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p. 725 - 728
(2007/10/03)
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- A novel and simple method to prepare γ-hydroxy-α,β-(E)-alkenoic esters from γ-keto-alkynoic esters
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A method to convert γ-keto-alkynoic esters to γ-hydroxy-α,β-(E)-alkenoic esters is described. This functional group transformation was accomplished in one step by means of NaBH4 reduction in methanol.
- Naka, Tadaatsu,Koide, Kazunori
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p. 443 - 445
(2007/10/03)
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- Catalytic Conversion of β,γ-Unsaturated Esters, Amides and Nitriles into γ-Alkoxy or γ-Hydroxy α,β-Unsaturated Derivatives induced by Persulfate Anion Oxidation of Diphenyl Diselenide
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The reaction of β,γ-unsaturated esters, amides and nitriles with catalytic amounts of diphenyl diselenide and an excess of ammonium persulfate in alcohols or in water affords γ-alkoxy or γ-hydroxy α,β-unsaturated derivatives, respectively, in good yields.
- Tiecco, Marcello,Testaferri, Lorenzo,Tingoli, Marco,Bagnoli, Luana,Santi, Claudio
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p. 637 - 639
(2007/10/02)
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- Preparation and Rearrangement of cis-Methyl 3,4-Epoxy-4-(4'-methylphenyl)butanoate
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AlCl3 catalysed bromination of methyl 4-keto-4-(4'-methylphenyl)butanoate (2) is regioselective and furnishes methyl 3-bromo-4-keto-4-(4'-methylphenyl)butanoate (3). 3 on NaBH4 reduction in the presence of NaHCO3 furnishes a mixture of cis-methyl 3,4-epoxy-4-(4'-methylphenyl)butanoate (9), methyl (E)-4-hydroxy-4-(4'-methylphenyl)but-2-enoate (12), 4-(4'-methylphenyl)butanolide (26) and 2. 12 can be transformed to 1 on heating with NaOH-ethanol.BF3 catalysed rearrangement of 9 furnishes methyl 3-keto-4-(4'-methylphenyl)butanoate (17).The sequence of reactions 2->3->9->17 constitutes an interesting example of ketone transposition and provides a convenient route for the preparation of 17 from the readily available 2.
- Bhat, K. S.,Rao, A. S.
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p. 355 - 358
(2007/10/02)
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