- Site-Selective Acceptorless Dehydrogenation of Aliphatics Enabled by Organophotoredox/Cobalt Dual Catalysis
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The value of catalytic dehydrogenation of aliphatics (CDA) in organic synthesis has remained largely underexplored. Known homogeneous CDA systems often require the use of sacrificial hydrogen acceptors (or oxidants), precious metal catalysts, and harsh reaction conditions, thus limiting most existing methods to dehydrogenation of non- or low-functionalized alkanes. Here we describe a visible-light-driven, dual-catalyst system consisting of inexpensive organophotoredox and base-metal catalysts for room-temperature, acceptorless-CDA (Al-CDA). Initiated by photoexited 2-chloroanthraquinone, the process involves H atom transfer (HAT) of aliphatics to form alkyl radicals, which then react with cobaloxime to produce olefins and H2. This operationally simple method enables direct dehydrogenation of readily available chemical feedstocks to diversely functionalized olefins. For example, we demonstrate, for the first time, the oxidant-free desaturation of thioethers and amides to alkenyl sulfides and enamides, respectively. Moreover, the system's exceptional site selectivity and functional group tolerance are illustrated by late-stage dehydrogenation and synthesis of 14 biologically relevant molecules and pharmaceutical ingredients. Mechanistic studies have revealed a dual HAT process and provided insights into the origin of reactivity and site selectivity.
- Zhou, Min-Jie,Zhang, Lei,Liu, Guixia,Xu, Chen,Huang, Zheng
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supporting information
p. 16470 - 16485
(2021/10/20)
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- Bio-based vinylphenol family: Synthesis via decarboxylation of naturally occurring cinnamic acids and living radical polymerization for functionalized polystyrenes
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A series of bio-based vinylphenols or hydroxystyrenes is prepared by simple decarboxylation of various naturally occurring cinnamic acids such as o-, m-, and p-coumaric; caffeic; ferulic; and sinapinic acids, which possess hydroxy groups and other substituents at different positions on the aromatic ring. After protection of the phenolic moieties with trialkylsilyl groups, reversible addition–fragmentation chain-transfer polymerization is accomplished with cumyl dithiobenzoate to afford various bio-based hydroxyl-protected polystyrenes with controlled molecular weights and narrow molecular weight distributions. Subsequent deprotection of the silyl groups under mild conditions results in a series of well-defined functionalized polystyrenes possessing different numbers (mono-, di-, tri-) of hydroxy groups at different positions (o, m, p). The obtained functionalized polystyrenes show unique thermal properties depending on the substituents, and those with phenol and catechol groups serve as reducing agents for silver ions.
- Takeshima, Hisaaki,Satoh, Kotaro,Kamigaito, Masami
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- Total Synthesis of Gombamide A
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The first total synthesis of Gombamide A (1), a cytotoxic cyclic thiopeptide from the sponge Clathria gombawuiensis, has been achieved. Highlights of the convergent synthesis feature a disulfide bond forming cascade to close the 17-membered macrocycle and a selenoazidylation procedure to access the unusual para-hydroxystyrlyamide (pHSA) moiety. The synthesis required 18 steps, 11 steps in its longest linear sequence, and proceeded in 9.1% overall yield. This work will facilitate the study of the biological effects of Gombamide A and provide groundwork to explore the structure-activity relationship around this rare natural product.
- Garcia-Barrantes, Pedro M.,Lindsley, Craig W.
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supporting information
p. 3810 - 3813
(2016/08/16)
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- Catalytic wittig reactions of semi- and nonstabilized ylides enabled by ylide tuning
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The first examples of catalytic Wittig reactions with semistabilized and nonstabilized ylides are reported. These reactions were enabled by utilization of a masked base, sodium tert-butyl carbonate, and/or ylide tuning. The acidity of the ylide-forming proton was tuned by varying the electron density at the phosphorus center in the precatalyst, thus facilitating the use of relatively mild bases. Steric modification of the precatalyst structure resulted in significant enhancement of E selectivity up to >95:5, E/Z. Time for a tune up: Catalytic Wittig reactions with semi- and nonstabilized ylides were enabled by use of a masked base (NaOCO2tBu) and/or ylide tuning. The acidity of the ylide-forming proton was tuned by varying the electron density at the P center in the precatalyst, thus facilitating the use of relatively mild bases. Steric modification of the precatalyst structure resulted in significant enhancement of E selectivity.
- Coyle, Emma E.,Doonan, Bryan J.,Holohan, Andrew J.,Walsh, Killian A.,Lavigne, Florie,Krenske, Elizabeth H.,O'Brien, Christopher J.
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supporting information
p. 12907 - 12911
(2016/02/18)
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- Bifunctional polymeric organocatalysts and their application in the cooperative catalysis of Morita-Baylis-Hillman reactions
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A series of soluble, noncross-linked polystyrene-supported tri-phenylphosphane and 4-dimethylaminopyridine reagents were prepared. Some of these polymeric reagents contained either alkyl alcohol or phenol groups on the polymer backbone. The use of these materials as organocatalysts in a range of Morita-Baylis-Hillman reactions indicated that hydroxyl groups could participate in the reactions and accelerate product formation. In the cases examined, phenol groups were more effective than alkyl alcohol groups for catalyzing the reactions. This article is one of the first reports of the synthesis and use of non-natural, bifunctional polymeric reagents for use in organic synthesis in which both functional groups can cooperatively participate in the catalysis of reactions.
- Kwong, Cathy Kar-Wing,Huang, Rui,Zhang, Minjuan,Shi, Min,Toy, Patrick H.
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p. 2369 - 2376
(2008/02/02)
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- The kulinkovich reaction in the synthesis of constrained N,N-dialkyl neurotransmitter analogues
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An intermolecular Ti(IV)-mediated cyclopropanation reaction has been used to synthesize substituted 2-phenylcyclopropylamines and constrained analogues of the neurotransmitters histamine and tryptamine. Many hydroxy- and methoxy-substituted phenylcyclopropylamines are known to inhibit monoamine oxidase and have been shown to mimic hallucinogens. These compounds were made in 1 to 5 steps from readily available starting materials.
- Faler, Catherine A.,Joullie, Madeleine M.
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p. 1987 - 1990
(2008/02/02)
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- Metallocene-mediated synthesis of chain-end functionalized polypropylene and application in PP/clay nanocomposites
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This paper summarizes our research in the preparation of chain end functionalized isotactic polypropylene (PP) having a terminal functional group, such as Cl, OH, and NH2. The chemistry involves metallocene-mediated propylene polymerization usi
- Chung
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p. 6292 - 6299
(2007/10/03)
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