Esters heteroaromatic compounds

Silver(I) triflate is widely applied to the preparation of various derivatives of triflic acid, both covalent esters [66] and ionic salts For example, it can be used for the in situ generation of iodine([) triflate, a very effective lodinatmg reagent for aromatic and heteroaromatic compounds [130] (equations 65 and 66)... 

N-Heteroaromatic compounds like pyridine, pyridazine, pyrazine, isoquinoline, and their derivatives42,250 react with diphenyl cyclopropenone in a formal (3+2) cycloaddition mode to the C=N bond of the heterocycle. As expected from the results discussed earlier (p. 67), the reaction is initiated by attack of nitrogen at the cyclopropenone C3 position and followed by stabilization of the intermediate betaine 390 through nucleophilic interaction of the Cl/C3 bond with the activated a-site of the heterocycle, giving rise to derivatives of 2-hydroxy pyrrocoline 391—394). In some cases, e.g. diphenyl cyclopropenone and pyridine42, further interaction with a second cyclopropenone molecule is possible under the basic conditions leading to esters of type 392. 

C Yamagami, M Yokota, N Takao. Hydrogen bond effects of ester and amide groups in heteroaromatic compounds on the relationship between the capacity factor and the octanol-water partition coefficients. J. Chromatogr. A 662 49-60 (1994). 

Yamagami, C., Takao, N. (1992) Hydrophobicity parameters determined by reversed-phase liquid chromatography. V. Relationship between capacity factor and the octanol-water partition coefficient for simple heteroaromatic compounds and their ester derivatives. Chem. Pharm. Bull. 40(4), 925-929. 

Vinylsilanes can function as a silylating reagents for C-H bonds in heteroaromatic compounds (Scheme 5) [12]. The reaction of furan 7 with vinylsilane 8 using Ru3(CO)12 as a catalyst affords the /1-silylation product in 98 % yield. This silylation can be applied only to heteroaromatic esters, ketones, and amides. For this reaction, RuHCl(CO)(PPh3)3 also has catalytic activity. 

Boron-substituted heteroaromatic compounds 89AHC(46)143. Dithiocarboxyl esters 88SR(8)155. 

Moreover, the selenol esters can acylate reactive arenes and heteroaromatic compounds when cop-per(I) triflate is employed as the selenophilic metal cation. - The acylation of aromatics by use of the benzene complex of copper(I) triflate (43 Scheme 12) was complete within an hour at room temperature, with benzene as solvent, and the acylation products were obtained in high yields. Intramolecular acylation was examined successfully, as shown in equation (20). 

There are no novel results concerning acylcarbene transfer to C-C double bonds of heteroaromatic compounds such as thiophene and furan under photochemical conditions (see Houben-Weyl, Vol. 4/3, p288). More recent studies have focussed completely on the transition metal catalyzed version which, especially for a-diazo esters as Cj building blocks, displays higher efficiency and broader scope, whereas it often yields products other than cyclopropanes when a-diazo ketones are employed, see Section 1.2.1.2.4.2.6.3. and Houben-Weyl, Vol. E19b, ppll56, 1283, and 1332. 

Copper powder, copper bronze, Cu O, CuO, CuSO, CuCl and CuBr were the first catalysts which were used routinely for cyclopropanation of olefins as well as of aromatic and heteroaromatic compounds with diazoketones and diazoacetates. Competing insertion of a ketocarbene unit into a C—H bond of the substrate or solvent remained an excpetion in contrast to the much more frequent intramolecular C—H insertion reactions of appropriately substituted a-diazoketones or diazoacetates Reviews dealing with the cyclopropanation chemistry of diazo-acetic esters (including consideration of the efficiency of the copper catalysts mentioned above) and diazomalonic esters as well as with intramolecular cyclopropanation reactions of diazoketones have appeared. 

Azo Compounds, Azirines, Diazirines, Diazo Compounds, Diazonium Salts, Azides,. V-Oxides, Nitrite Esters and Heteroaromatic Compounds Photofragmentation and Photorearrangement... 

The migration reaction has been reported for both heteroaromatic acid phenyl esters154 184 and hydroxypyridine esters.185 The former report describes the process for both 3- and 4-isomers of (150) and for the 5-ring heteroaromatic compounds... 

Dimethyl malonate derivatives containing an allenyl sulfone substituent at the y- or 3-position undergo endo-mode ring closure to give cyclopentene or cyclohexene derivatives upon treatment with 1.5 equiv of t-BuOK in t-BuOH at rt. The intermediate unsaturated cycloadducts undergo demethoxycarbonylation and double bond isomerization under the reaction conditions (eq 53). Other active methine compounds behave similarly. A threefold excess of i-BuOK is more effective than certain amine bases for the conversion of phenylsulfonyl methyl derivatives of aromatic or heteroaromatic compounds into the corresponding dithio esters upon reaction with an excess of elemental sulfur. ... 

Catalytic AFC reactions of indoles have attracted considerable attention, and there has been significant progress in this area since 2009. Catalytic AFC reactions of aromatic and heteroaromatic compounds with a-imino esters provide a direct approach to optically pure aryl and heteroaryl glycines. In 2009, You and co-workers realized the AFC reaction of indoles with ethyl glyoxylate imine with 10 mol% of chiral phosphoric acid (S)-13b, affording (3-indolyl)glycine derivatives 28 in excellent yields (85-93%) with up to 87% ee (Scheme 6.11). ... 

Lithium-halogen exchange of bromide mainly followed by fluorination with NFSi is a standard approach for regioselective installation of a fluorine atom onto aromatic and heteroaromatic compounds. Fluorinated products obtained through this synthetic sequence, include 2-amino-5-fluorothiazole, 4-fluoro-17/-pyrrolo[2,3-h] pyridine (eq 36), 5-fluoro-1-naphthalenecarboxylic ester, and 3,7-difluoro-4,8-bis(2-ethylhexyloxy)benzo[ 1,2-h 4,5-h ]dithiophene. ... 

One of the most reliable methods for the construction of an oligoheteroarene structure is the transition-metal-catalyzed cross-coupling reaction [26]. However, a problem to be overcome remains in the cross-coupling. The installation of a metal group into heteroaromatic compounds is often dififlcult because of problems with the stability of the resulting heteroaromatic metal reagent [27]. For example, 2-pyridyl boronic acid and its esters are easily decomposed by proton [28]. In addition to this problem with stability, the transmetallation of an electron-deficient heteroaromatic boron reagent to palladium is relatively slow [29]. 

As the C4 hydroxyl group can be readily replaced with halogen (Cl, Br) and the ester can be spht off by saponification and decarboxylation, this approach opens access to a variety of multiply functionafized labeled heteroaromatic compounds. 

In the reaction of Q,/3-unsaturated ketones and esters, sometimes simple Michael-type addition (insertion and hydrogenolysis, or hydroarylation, and hydroalkenylation) of alkenes is observed[53,54]. For example, a simple addition product 56 to methyl vinyl ketone was obtained by the reaction of the heteroaromatic iodide 55[S5]. The corresponding bromide affords the usual insertion-elimination product. Saturated ketones are obtained cleanly by hydroarylation of o,/3l-unsaturated ketones with aryl halides in the presence of sodium formate, which hydrogenolyses the R—Pd—I intermediate to R— Pd—H[56]. Intramolecular hydroarylation is a useful reaction. The diiodide 57 reacts smoothly with sodium formate to give a model compound for the afla-toxin 58. (see Section 1.1.6)[57]. Use of triethylammonium formate and BU4NCI gives better results. 

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