- Biomimetic Syntheses of Analogs of Hongoquercin A and B by Late-Stage Derivatization
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The hongoquercins are tetracyclic meroterpenoid natural products with the trans-transoid decalin-dihydrobenzopyran ring system, which display a range of different bioactivities. In this study, the syntheses of a range of hongoquercins using gold-catalyzed enyne cyclization reactions and further derivatization are described. The parent enyne resorcylate precursors were synthesized biomimetically from the corresponding dioxinone keto ester via regioselective acylation, Tsuji-Trost allylic decarboxylative rearrangement, and aromatization. The dioxinone keto ester 12 was prepared in 6 steps from geraniol using allylic functionalization and alkyne synthesis.
- Mies, Thomas,White, Andrew J. P.,Parsons, Philip J.,Barrett, Anthony G. M.
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p. 1802 - 1817
(2021/01/13)
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- Catalytic Metal-free Allylic C?H Amination of Terpenoids
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The selective replacement of C?H bonds in complex molecules, especially natural products like terpenoids, is a highly efficient way to introduce new functionality and/or couple fragments. Here, we report the development of a new metal-free allylic amination of alkenes that allows the introduction of a wide range of nitrogen functionality at the allylic position of alkenes with unique regioselectivity and no allylic transposition. This reaction employs catalytic amounts of selenium in the form of phosphine selenides or selenoureas. Simple sulfonamides and sulfamates can be used directly in the reaction without the need to prepare isolated nitrenoid precursors. We demonstrate the utility of this transformation by aminating a large set of terpenoids in high yield and regioselectivity.
- Teh, Wei Pin,Obenschain, Derek C.,Black, Blaise M.,Michael, Forrest E.
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supporting information
p. 16716 - 16722
(2020/11/09)
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- Cesium Carbonate Catalyzed Esterification of N-Benzyl- N-Boc-amides under Ambient Conditions
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We report a general activated amide to ester transformation catalyzed by Cs2CO3. Using this approach, esterification proceeds under relatively mild conditions and without the need for a transition metal catalyst. This method exhibits broad substrate scope and represents a practical alternative to existing esterification strategies. The synthetic utility of this protocol is demonstrated via the facile synthesis of crown ether derivatives and the late-stage modification of a representative natural product and several sugars in reasonable yields.
- Ye, Danfeng,Liu, Zhiyuan,Chen, Hao,Sessler, Jonathan L.,Lei, Chuanhu
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supporting information
p. 6888 - 6892
(2019/09/07)
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- Nucleophilic Substitutions of Alcohols in High Levels of Catalytic Efficiency
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A practical method for the nucleophilic substitution (SN) of alcohols furnishing alkyl chlorides, bromides, and iodides under stereochemical inversion in high catalytic efficacy is introduced. The fusion of diethylcyclopropenone as a simple Lewis base organocatalyst and benzoyl chloride as a reagent allows notable turnover numbers up to 100. Moreover, the use of plain acetyl chloride as a stoichiometric promotor in an invertive SN-type transformation is demonstrated for the first time. The operationally straightforward protocol exhibits high levels of stereoselectivity and scalability and tolerates a variety of functional groups.
- Stach, Tanja,Dr?ger, Julia,Huy, Peter H.
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supporting information
p. 2980 - 2983
(2018/05/28)
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- Systematic Evaluation of Sulfoxides as Catalysts in Nucleophilic Substitutions of Alcohols
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Herein, a method for the nucleophilic substitution (SN) of benzyl alcohols yielding chloro alkanes is introduced that relies on aromatic sulfoxides as Lewis base catalysts (down to 1.5 mol-%) and benzoyl chloride (BzCl) as reagent. A systematic screening of various sulfoxides and other sulfinyl containing Lewis bases afforded (2-methoxyphenyl)methyl sulfoxide as optimal catalyst. In contrast to reported formamide catalysts, sulfoxides also enable the application of plain acetyl chloride (AcCl) as reagent. In addition, it was demonstrated that weakly electrophilic carboxylic acid chlorides like BzCl promote Pummerer rearrangement of sulfoxides already at room temperature. This side-reaction also provided the explanation, why sulfoxide catalyzed SN-reactions of alcohols do not allow the effective production of aliphatic and electron deficient chloro alkanes. Comparison experiments provided further insight into the reaction mechanism.
- Motsch, Sebastian,Schütz, Christian,Huy, Peter H.
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supporting information
p. 4541 - 4547
(2018/09/13)
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- Fluoride-Catalyzed Esterification of Amides
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In recent years, it has been demonstrated that amide carbon–nitrogen bonds can be activated and selectively cleaved using transition metal catalysts. However, these methodologies have been restricted to specific amides; a one-to-one relationship exists between the catalytic system and the amides and also uses large amounts of transition-metal catalysts and ligands. Hence, we now report a general strategy for esterification of common amides using fluoride as a catalyst. This method shows high functional group tolerance, and notably it requires only a slight excess of the alcohol nucleophile, which is a rare case in transition-metal-free amide transformations. Moreover, this approach may provide a new understanding for further studies on esterification of amides and is expected to stimulate the development of alternative methods for direct functionalization of amides.
- Wu, Hongxiang,Guo, Weijie,Daniel, Stelck,Li, Yue,Liu, Chao,Zeng, Zhuo
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p. 3444 - 3447
(2018/02/21)
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- Widely Applicable Hydrofluorination of Alkenes via Bifunctional Activation of Hydrogen Fluoride
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Expanding the use of fluorine in pharmaceuticals, agrochemicals and materials requires a widely applicable and more efficient protocol for the preparation of fluorinated compounds. We have developed a new generation nucleophilic fluorination reagent, KHSO4-13HF, HF 68 wt/wt %, that is not only easily handled and inexpensive but also capable of hydrofluorinating diverse, highly functionalized alkenes, including natural products. The high efficiency observed in this reaction hinges on the activation of HF using a highly "acidic" hydrogen bond acceptor.
- Lu, Zhichao,Zeng, Xiaojun,Hammond, Gerald B.,Xu, Bo
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supporting information
p. 18202 - 18205
(2017/12/28)
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- METHOD OF CONVERTING ALCOHOL TO HALIDE
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The present invention relates to a method of converting an alcohol into a corresponding halide. This method comprises reacting the alcohol with an optionally substituted aromatic carboxylic acid halide in presence of an N-substituted formamide to replace a hydroxyl group of the alcohol by a halogen atom. The present invention also relates to a method of converting an alcohol into a corresponding substitution product. The second method comprises: (a) performing the method of the invention of converting an alcohol into the corresponding halide; and (b) reacting the corresponding halide with a nucleophile to convert the halide into the nucleophilic substitution product.
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-
Page/Page column 182; 183; 184
(2017/01/02)
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- Efficient O-Acylation of Alcohols and Phenol Using Cp2TiCl as a Reaction Promoter
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A method has been developed for the conversion of primary, secondary, and tertiary alcohols, and phenol, into the corresponding esters at room temperature. The method uses a titanium(III) species generated from a substoichiometric amount of titanocene dichloride together with manganese(0) as a reductant, as well as methylene diiodide. It involves a transesterification from an ethyl ester, or a reaction with an acyl chloride. A radical mechanism is proposed for these transformations.
- Durán-Pe?a, María Jesús,Botubol-Ares, José Manuel,Hanson, James R.,Hernández-Galán, Rosario,Collado, Isidro G.
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supporting information
p. 3584 - 3591
(2016/07/28)
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- Gd(OTf)3-catalyzed synthesis of geranyl esters for the intramolecular radical cyclization of their epoxides mediated by titanocene(III)
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A selective and mild method for the esterification of a variety of carboxylic acids with geraniol is developed. We demonstrated that the use of triphenylphosphine, I2, 2-methylimidazole or imidazole and a catalytic amount of Gd(OTf)3 resulted to be more active than the previous protocols, providing a 16-membered library of geranyl esters in higher yields and in shorter reaction times. The use of essential oil of palmarosa (Cymbopogon martinii), enriched with geraniol, as a raw material for the synthesis of the target compounds complemented and proved how sustainable and eco-friendly this protocol is. Finally, the selective 6,7-epoxidation of the obtained geranyl esters led us to study their regio-controlled radical cyclization mediated by titanocene(iii) for the synthesis of novel (8-hydroxy-9,9-dimethyl-5-methylene cyclohexyl)methyl esters in moderate yields and with excellent stereoselectivities.
- Garca Santos, William H.,Puerto Galvis, Carlos E.,Kouznetsov, Vladimir V.
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p. 1358 - 1366
(2015/02/05)
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- Copper-catalyzed cross-coupling of thiols, alcohols, and oxygen for the synthesis of esters
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Copper-catalyzed, one-pot, three-component coupling reactions using thiols, alcohols, and oxygen to form a variety of esters in good yields were studied. In the presence of easily oxidized benzylic and allylic alcohols, thiols were selectively oxidized to form thionoesters, which underwent facile S/O exchange to afford esters. Thiols may be used as an alternative benzoyl source under mild aerobic conditions.
- Lim, Seungyeon,Ji, Miran,Wang, Xi,Lee, Chan,Jang, Hye-Young
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supporting information
p. 591 - 595
(2015/01/30)
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- Organocatalytic selective benzoylation of alcohols with trichloromethyl phenyl ketone: Inverse selectivity in benzoylation of alcohols containing phenol or aromatic amine functionality
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Trichloromethyl phenyl ketone benzoylates primary and secondary aliphatic alcoholic groups in compounds also containing a phenolic group in the presence of 2-10 mol % of PMDETA organocatalyst at room temperature in high yields and excellent selectivity. It also shows the potential to selectively benzoylate primary alcoholic groups of aminoarylalkanols and primary-secondary diols as well as primary amino group of alkyl amines in the presence of aryl amines under similar conditions. A rationale for the selectivity and efficiency of the reaction has been provided.
- Ram, Ram N.,Soni, Vineet Kumar,Gupta, Dharmendra Kumar
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p. 9068 - 9075
(2012/11/07)
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- Ligand-assisted rate acceleration in lanthanum
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The transesterification of an equimolar mixture of carboxylic esters and primary (1°), secondary (2°), and tertiary (3°) alcohols in hydrocarbon solvents was promoted with high efficiency by a lanthanum(III) complex, which was prepared in situ from lanthanum (III) isopropoxide (1 mol %) and 2-(2-methoxyethoxy)ethanol (2 mol %). The present La(III) catalyst was highly effective for the chemoselective transesterification in the presence of competitive 1°-and 2°-amines. Remarkably, esters were obtained in good to excellent yields as colorless materials without an inconvenient workup procedure.
- Hatano, Manabu,Furuya, Yoshiro,Shimmura, Takumi,Moriyama, Katsuhiko,Kamiya, Sho,Maki, Toshikatsu,Ishihara, Kazuaki
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supporting information; experimental part
p. 426 - 429
(2011/04/15)
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- Cl3CCONH2/PPh3: A versatile reagent for synthesis of esters
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Cl3CCONH2/PPh3 was a versatile reagent to convert carboxylic acids into their corresponding acid chlorides. This intermediate was clearly confirmed by spectroscopic methods (IR, 1H, 13C NMR). This one-pot reaction of in situ acid chloride generated with various alcohols successfully furnished the corresponding esters in moderate to excellent yields. Copyright ? Taylor & Francis Group, LLC.
- Chantarasriwong, Oraphin,Jang, Doo Ok,Chavasiri, Warinthorn
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scheme or table
p. 2845 - 2856
(2009/04/11)
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- Efficient transesterification/acylation reactions mediated by N-heterocyclic carbene catalysts
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Imidazol-2-ylidenes, a family of N-heterocyclic carbenes (NHC), are efficient catalysts in the transesterification involving numerous esters and alcohols. Low catalyst loadings of aryl- or alkyl-substituted NHC catalysts mediate the acylation of alcohols with enol acetates in short reaction times at room temperature. Commercially available and more difficult to cleave methyl esters react with primary alcohols in the presence of alkyl-substituted NHC to efficiently form the corresponding esters. While primary alcohols are selectively acylated over secondary alcohols with use of enol esters as acylating agents, methyl and ethyl esters can be employed as protective agents for secondary alcohols in the presence of the more active alkyl-substituted NHC catalysts. The NHC-catalyzed transesterification protocol was simplified by generating the imidazol-2-ylidene catalysts in situ.
- Grasa, Gabriela A.,Gueveli, Tatyana,Singh, Rohit,Nolan, Steven P.
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p. 2812 - 2819
(2007/10/03)
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- Efficient method for the preparation of carboxylic acid alkyl esters or alkyl phenyl ethers by a new-type of oxidation-reduction condensation using 2,6-dimethyl-1,4-benzoquinone and alkoxydiphenylphosphines
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A new-type of oxidation-reduction condensation proceeded smoothly to afford carboxylic acid alkyl esters or alkyl phenyl ethers in good to high yields by combined use of alkoxydiphenylphosphines (1) having primary, bulky secondary or tertiary alkoxy groups, a mild quinone-type oxidant such as 2,6-dimethyl-1,4-benzoquinone (DMBQ) and carboxylic acids or phenols. Generally, alkoxydiphenylphosphines were prepared easily from chlorodiphenylphosphine (2) and alcohols in the presence of pyridine, and were isolated by distillation. On the other hand, the phosphines 1 were also prepared in situ from N,N-dimethylaminodiphenylphosphine (3a) and primary or secondary alcohols while primary, bulky secondary or tertiary alkoxydiphenylphosphines were alternatively formed in situ by adding 2 to the "BuLi-treated alcohols in order to perform the above reactions by a one-pot procedure from alcohols and nucleophiles. The reaction of thus formed 1, DMBQ and carboxylic acids or phenols afforded the corresponding alkylated products, including hindered secondary and tertiary alkylated ones, in good to high yields at room temperature. In the case of using chiral secondary alcohols, the corresponding carboxylic acid alkyl esters were obtained as well in high yields with perfect inversion of stereochemistry by SN2 replacement.
- Shintou, Taichi,Kikuchi, Wataru,Mukaiyama, Teruaki
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p. 1645 - 1667
(2007/10/03)
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- High-Load, ROMP-Generated Oligomeric Bis-acid Chlorides: Design of Soluble and Insoluble Nucleophile Scavengers
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(Equation presented) An efficient strategy for scavenging a host of nucleophiles utilizing an oligomeric bis-acid chloride (OBAC), generated from the ROM polymerization of trans-bicyclo[2.2.1]hept-5-ene-2,3-dicarbonyl dichloride, is described. The reactivity and high load of the OBAC reagent is exploited in the scavenging of amines, alcohols, and thiols that are present in excess following a common benzoylation event. Following the scavenging event, these oligomers can be precipitated with EtOAc and filtered (SiO2), leaving benzoylated nucleophiles in excellent yield and purity.
- Moore, Joel D.,Byrne, Robert J.,Vedantham, Punitha,Flynn, Daniel L.,Hanson, Paul R.
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p. 4241 - 4244
(2007/10/03)
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- Scavenge-ROMP-filter: a facile strategy for soluble scavenging via norbornenyl tagging of electrophilic Reagents.
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[reaction: see text] A new "chemical tagging" method for homogeneous electrophilic scavenging is described. The method utilizes 5-norbornene-2-methanol to scavenge/tag a variety of electrophiles that are present in excess. Once tagging is complete, the crude reaction mixture is subjected to a rapid ROM polymerization event utilizing the second generation Grubbs catalyst. This process yields a polymer that can be precipitated with methanol or ether/hexane, leaving products in excellent yield and purity.
- Moore, Joel D,Harned, Andrew M,Henle, Julia,Flynn, Daniel L,Hanson, Paul R
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p. 1847 - 1849
(2007/10/03)
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- Selective 1,5-Diene Synthesis. A Radical Approach
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A new synthetic route to 1,5-dienes is described.Irradiation of a mixture of allyl bromides and allyl sulfides in the presence of hexamethylditin gives the cross-coupled products selectively.
- Yanagisawa, Akira,Noritake, Yoshiyuki,Yamamoto, Hisashi
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p. 1899 - 1902
(2007/10/02)
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- Synthesis of (+/-)-trixagol by an electrophilic cyclization of an allylsilane
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1,5-Dienes containing an allylsilane are cyclized by Lewis acids to methylenecyclohexanes.The trimethylsilyl group exerts a strong activating and directing influence on the regioselectivity of this cyclization.The monocyclic compound 10 was converted into the diterpene, (+/-)-trixagol (3).
- Armstrong, Rosemary J.,Weiler, Larry
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p. 2530 - 2539
(2007/10/02)
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