- Combined Photoredox and Carbene Catalysis for the Synthesis of γ-Aryloxy Ketones
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N-heterocyclic carbenes (NHCs) have emerged as catalysts for the construction of C?C bonds in the synthesis of substituted ketones under single-electron processes. Despite these recent reports, there still remains a need to increase the utility and practicality of these reactions by exploring new radical coupling partners. Herein, we report the synthesis of γ-aryloxyketones via combined NHC/photoredox catalysis. In this reaction, an α-aryloxymethyl radical is generated via oxidation of an aryloxymethyl potassium trifluoroborate salt, which is then added into styrene derivatives to provide a stabilized benzylic radical. Subsequent radical-radical coupling reaction with an azolium radical affords the γ-aryloxy ketone products. (Figure presented.).
- Wang, Pengzhi,Fitzpatrick, Keegan P.,Scheidt, Karl A.
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supporting information
p. 518 - 524
(2021/12/16)
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- Practical Chemoselective Acylation: Organocatalytic Chemodivergent Esterification and Amidation of Amino Alcohols with N-Carbonylimidazoles
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Chemoselective transformations are a cornerstone of efficient organic synthesis; however, achieving this goal for even simple transformations, such as acylation reactions, is often a challenge. We report that N-carbonylimidazoles enable catalytic chemodivergent aniline or alcohol acylation in the presence of pyridinium ions or 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), respectively. Both acylation reactions display high and broad chemoselectivity for the target group. Unprecedented levels of chemoselectivity were observed in the DBU-catalyzed esterification: A single esterification product was obtained from a molecule containing primary aniline, alcohol, phenol, secondary amide, and N?H indole groups. These acylation reactions are highly practical as they involve only readily available, inexpensive, and relatively safe reagents; can be performed on a multigram scale; and can be used on carboxylic acids directly by in situ formation of the acylimidazole electrophile.
- Nelson, Hope,Richard, William,Brown, Hailee,Medlin, Abigail,Light, Christina,Heller, Stephen T.
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supporting information
p. 22818 - 22825
(2021/09/13)
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- Chemoselective acylation of 2-amino-8-quinolinol in the generation of C2-amides or C8-esters
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Two different ways to carry out the chemoselective acylation of 2-amino-8-quinolinol with unique features to generate C2-amides or C8-esters were developed. The coupling reaction with a variety of carboxylic acids using EDCI and DMAP provided C8-ester derivatives, whereas N-heteroaromatic acids were not introduced on the C8-hydroxy group, but rather on the C2-amino group under the same conditions. To obtain C2-amides selectively, the anionic nucleophile from 2-amino-8-quinolinol was treated with less reactive acyl imidazolides or esters.
- Park, Yongseok,Fei, Xiang,Yuan, Yue,Lee, Sanha,Hur, Joonseong,Park, Sung Jean,Jung, Jae-Kyung,Seo, Seung-Yong
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p. 41955 - 41961
(2017/09/12)
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- Enantioselective synthesis of α-amino acids from N-tosyloxy β-lactams derived from β-keto esters
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A novel synthetic sequence has been developed to convert simple β-keto esters into enantiomerically enriched α-amino acids. The key features of this sequence include the addition of azide to the C3 position of β-keto ester derived N-tosyloxy-β-lactams through a concomitant nucleophilic addition/N-O bond reduction reaction, a mild CsF-induced N1 benzylation of α-azido monocyclic β-lactams, the preparation of α-keto-β-lactams through a novel four-step sequence from the corresponding 3-azido-1-benzyl-β-lactams, and TEMPO-mediated ring expansion of these compounds to the corresponding N-carboxy anhydrides (NCAs). In addition, the synthesis, isolation, and characterization of unusual 3-imino and 3-chloramino-β-lactams is reported.
- Durham, Timothy B.,Miller, Marvin J.
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- Synthesis of S-thioacyl dithiophosphates, efficient and chemoselective thioacylating agents
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Easily available acyl dithiophosphates are not stable and isomerise reversibly to O-thioacyl monothiophosphates, especially when subjected to heating. Much slower but probably irreversible isomerisation to S-thioacyl monothiophosphates occurs. Since equilibrium states are established and S-thioacyl (mono)thiophosphates form slowly, reaction mixtures contain generally both thioacylating and acylating agents, and consequently cannot be used for efficient thioacylation. On the other hand, treatment of a mixture of isomeric anhydrides with an excess of a dithiophosphoric acid leads to exclusive formation of S-thioacyl dithiophosphates. They appear to be excellent thioacylating agents: relatively stable, inert towards water and oxygen and therefore easy to handle. Reactions with nitrogen or sulfur nucleophiles proceed very rapidly under ambient conditions, yielding respective thioacyl derivatives. Isolation of the products is very simple. Due to the low reactivity of S-thioacyl dithiophosphates towards oxygen nucleophiles they can be used for direct thioacylation of multifunctional nucleophiles with unprotected hydroxy groups. Respective thioacyl derivatives cannot readily be obtained using other methods.
- Doszczak, Leszek,Rachon, Janusz
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p. 1271 - 1279
(2007/10/03)
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- Stability studies of N-acylimidazoles
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Studies of the stabilities of a series of N-acylimidazoles towards acidic and basic conditions of potential usefulness for the removal of common temporary protection in peptide and oligonucleotide synthesis are presented. N-Acylimidazoles with a variety of substituents in the acyl component were prepared and treated with 3% trifluoroacetic acid (TFA) in chloroform and with 2% 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in N,N-dimethylformamide (DMF), the extent of their degradation being determined by proton NMR. N-(2,4,6-Trimethylbenzoyl)imidazole (1) and N-(2,6-dimethoxybenzoyl)-imidazole (2) remained unaffected under the above acidic and basic conditions after 4 d and 2 d, respectively. In addition, 1 and 2 were resistant to treatment with a solution of 2% piperidine/2% DBU in DMF for 24 h. Under ammonolytic conditions, 2 was rapidly cleaved (less than 1 h), whereas 1 was 64% degraded after 48 h, as ascertained by reversed-phase HPLC. Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002.
- Zaramella, Simone,Stroemberg, Roger,Yeheskiely, Esther
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p. 2633 - 2639
(2007/10/03)
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- Synthesis of N-(protected)aminophthalimides: Application to the synthesis of singly labelled isoniazid
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The synthesis of a series of N-(protected)aminophthalimides and the removal of their phthaloyl group leading to N-(protected) or N,N-bis(protected)hydrazines is described. As illustrated by the synthesis of monolabelled isoniazid 3b*, this strategy can be utilized for the preparation of monolabelled substituted hydrazines.
- Brosse, Nicolas,Pinto, Maria-Fatima,Jamart-Gregoire, Brigitte
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p. 3685 - 3688
(2007/10/03)
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- Use of N-pivaloyl imidazole as protective reagent for sugars
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N-Pivaloyl imidazole was prepared and used as a selective protective reagent of different monosaccharides (D-glucose, D-mannose, D-galactose, 2- acetamido-2-deoxy-D-glucose and 2-acetamido-2-deoxy-β-D-glucopyranosyl azide) and lactose. A variety of pivalates were obtained with moderate or good regioselectivity.
- Santoyo-Gonzalez, Francisco,Uriel, Clara,Calvo-Asin, Jose A.
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p. 1787 - 1792
(2007/10/03)
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- GENERAL METHOD OF PREPARATION OF N- DERIVATIVES OF HETEROCYCLIC BASES
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Reaction of (R)-1-O-p-toluenesulfonyl-1,2,3-propanetriol (IV) with N-trimethylacetylimidazole (II) afforded (R)-1-O-p-toluenesulfonyl-3-O-trimethylacetyl-1,2,3-propanetriol (V) which was reacted with dimethoxymethane in the presence of phosphorus pentoxide to give (R)-2-O-methoxymethyl-1-O-p-toluenesulfonyl-3-O-trimethylacetyl-1,2,3-propanetriol (VI).Compound VI was treated with acetic anhydride and boron trifluoride etherate and the obtained 2-acetoxy derivative VII reacted with bromotrimethylsilane to give the intermediary bromomethyl ether VIII.Compound VIII on reaction with tris(2-propyl) phosphite afforded (R)-2-O-bis(2-propyl)phosphonomethyl-1-O-p-toluenesulfonyl-3-O-trimethylacetyl-1,2,3-propanetriol (IX).Condensation of synthon IX with sodium salts of adenine, 2,6-diaminopurine, or with cytosine, 6-azacytozine or 2-chloroadenine in the presence of cesium carbonate, afforded fully protected diesters X and XIIIb which on methanolysis and reaction with bromotrimethylsilane gave N- derivatives of adenine (XIa), 2-chloroadenine (XIb), 2,6-diaminopurine (XIc), cytosine (XIVa) and 6-azacytosine (XIVb).In an analogous reaction, sodium salt of 4-methoxy-2-pyrimidone reacted with compound IX to give an intermediate XIIIa which on treatment with methanolic ammonia and subsequent deblocking under the same conditions also afforded the cytosine derivative XIVa.Sodium salt of 2-amino-6-chloropurine was in this way converted into the corresponding 2-aminopurine derivative XVIII.Deprotection of this compound gave 9-(S)-(3-hydroxy-2-phosphonomethoxypropyl)-2-aminopurine (XIX).
- Alexander, Petr,Holy, Antonin
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p. 1151 - 1163
(2007/10/02)
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- Acylimidazolides as Versatile Synthetic Intermediates for the Preparation of Sterically Congested Amides and Ketones: A Practical Synthesis of Proscar
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Acylimidazolides react with magnesium amides to produce carboxamides in excellent yields, whereas Fe(III) catalyzed cross coupling between acylimidazolide and Grignard reagents produce ketones in high yields.These methods were utilized to prepare the α-reductase inhibitor Proscar as well as various 17β-amide and ketone analogs of Δ1-4-aza-5α-androsten-3-one.
- Bhattacharya, A.,Williams, J.M.,Amato, J.S.,Dolling, U.-H.,Grabowski, E.J.J.
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p. 2683 - 2690
(2007/10/02)
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- A New Route to 1,3-Diacyl-2,3-dihydro-1H-imidazoles
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Preparative amounts of the title compounds can be prepared in high purity by hydrogenation of the corresponding 1,3-diacylimidazolium salts with sodium borohydride.Structures are confirmed by spectroscopic methods and in two cases by X-ray structure determination.
- Plath, Martin Wolfgang,Scharf, Hans-Dieter,Raabe, Gerhard,Krueger, Carl
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p. 951 - 955
(2007/10/02)
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- Facile Conversions of Carboxylic Acids into Amides, Esters, and Thioesters Using 1,1'-Oxalyldiimidazole and 1,1'-Oxalyldi(1,2,4-triazole)
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Aliphatic, aromatic, and heteroaromatic carboxylic acids react with 1,1'-oxalyldiimidazole (1) or 1,1'-oxalyldi(1,2,4-triazole) (2) in acetonitrile for 40 min at 40 degC to give the corresponding 1-acylazole intermediates (11), which promptly undergo aminolysis and alcoholysis to form amides (13) including dipeptides (14), esters (16), and thioesters (19).These findings show that both 1 and 2 can be utilized as condensing reagents for the synthesis of carboxylic acid derivatives.Keywords --- 1,1'-oxalyldiimidazole; 1,1'-oxalyldi(1,2,4-triazole); 1,1'-carbonyldiimidazole; 1-acylazole; condensing reagent; amidation; esterification; dipeptide; aminolysis; alcoholysis
- Kitagawa, Tokujiro,Kuroda, Hiroko,Sasaki, Hideaki,Kawasaki, Koichi
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p. 4294 - 4301
(2007/10/02)
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- A CONVENIENT ONE-POT PROCEDURE FOR SYNTHESIS OF THIOL ESTERS USING MAGNESIUM ION AS A CATALYST
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Various thiol esters (R1COSR2) were prepared in high yields by treatment of 1-acylimidazole with thiols in the presence of a catalytic amount of Mg(OEt)2.Malonic half-thiol esters 1OCOCH(R3)COSR2> were also prepared in good yields by treating magnesium monoalkyl malonate 1OCOCH(R3)COOMg0.5> with carbonyl-1,1'-diimidazole followed by addition of thiols.
- Ohta, Shunsaku,Okamoto, Masao
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p. 3245 - 3246
(2007/10/02)
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