- Copper-catalyzed vinylogous aerobic oxidation of unsaturated compounds with air
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A mild and operationally simple copper-catalyzed vinylogous aerobic oxidation of β,γ- and α,β-unsaturated esters is described. This method features good yields, broad substrate scope, excellent chemo- and regioselectivity, and good functional group tolerance. This method is additionally capable of oxidizing β,γ- and α,β-unsaturated aldehydes, ketones, amides, nitriles, and sulfones. Furthermore, the present catalytic system is suitable for bisvinylogous and trisvinylogous oxidation. Tetramethylguanidine (TMG) was found to be crucial in its role as a base, but we also speculate that it serves as a ligand to copper(II) triflate to produce the active copper(II) catalyst. Mechanistic experiments conducted suggest a plausible reaction pathway via an allylcopper(II) species. Finally, the breadth of scope and power of this methodology are demonstrated through its application to complex natural product substrates.
- Zhang, Hai-Jun,Schuppe, Alexander W.,Pan, Shi-Tao,Chen, Jin-Xiang,Wang, Bo-Ran,Newhouse, Timothy R.,Yin, Liang
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p. 5300 - 5310
(2018/04/24)
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- The reaction of photochemically generated α-hydroxyalkyl radicals with alkynes: a synthetic route to γ-butenolides
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The photomediated generation of α-hydroxyalkyl radicals from simple acyclic and cyclic alcohols, and acyclic diols, and their subsequent carbon-carbon bond forming reaction with propiolate esters and acetylenedicarboxylates, gives a mixture of a β-(hydroxyalkyl)enoate, the result of a formal cis addition, and the unsaturated lactone (γ-butenolide) resulting from the spontaneous cyclization of the corresponding trans addition product. Treatment of the cis adduct with NBS converts it to the same lactone, and so the method overall constitutes a particularly direct route to this important structural unit. Cyclic alcohols give rise to spiro-γ-butenolides. The use of supported photomediators simplifies product isolation and allows for the recovery and reuse of the photomediator.
- Geraghty, Niall W.A.,Hernon, Elaine M.
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scheme or table
p. 570 - 573
(2009/05/07)
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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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- Total synthesis of (+)-himbacine and (+)-himbeline
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Himbacine (1), a complex piperidine alkaloid isolated from the bark of Australian magnolias, is a promising lead in Alzheimer's disease research due to its potent muscarinic receptor antagonist property. We have described here a highly efficient synthetic strategy that resulted in the total synthesis of himbacine (1) in about 10% overall yield and isohimbacine (1a), an unnatural isomer of himbacine, in 18% overall yield. The total synthesis of himbacine was initially approached using an intramolecular Diels-Alder reaction as the key step to generate intermediate 5 followed by a [3 + 2] cycloaddition with nitrone 4 to produce the isoxazolidine derivative 3. Methylation followed by catalytic reduction of 3 gave 12'-hydroxyhimbacine (20), which, upon dehydration, gave isohimbacine (1a) as the sole product. In an alternative approach, an all-encompassing intramolecular Diels-Alder reaction of an appropriately substituted tetraene derivative 31, which bears the entire latent carbon framework and functional group substitution of himbacine, gave the desired advanced tricyclic intermediate 33, which was readily converted to (+)-himbeline (2) and (+)-himbacine (1).
- Chackalamannil, Samuel,Davies, Robert J.,Wang, Yuguang,Asberom, Theodros,Doller, Dario,Wong, Jesse,Leone, Daria,McPhail, Andrew T.
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p. 1932 - 1940
(2007/10/03)
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- REGIOCHEMICAL DIVERSITY IN ALLYLIC ALKYLATIONS VIA MOLYBDENUM CATALYSTS
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The use of molybdenum as a template to control regioselectivity in allylic alkylations is explored.The feasibility of performing allylic alkylations with preformed ?-allylmolybdenum comlplexes is established.As in palladium reactions, addition of excess phosphine has a profound effect on the rate these reactions.A catalytic reaction based upon molybdenum hexacarbonyl is developed.Using malonate anion, excellent regioselectivity for attack at the more substituted end of an allyl system regardless of the positional identity of the initial leaving group exists.With β-ketoesters, substrates which possess a secondary and a primary carbon in the allyl unit lead to preferential attack at the secondary carbon.However, substrates that possess a tertiary and a primary carbon at the termini lead to attack at the primary carbon.Anions derived from substituted malonates and 1,3-diketones lead to substitution at the less substituted position of allyl systems.The presence of strongly electron withdrawing substituents has little effect on these orientational blases.Mechanistic implications of these results are discussed.
- Trost, Barry M.,Lautens, Mark
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p. 4817 - 4840
(2007/10/02)
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