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Search for "regioisomers" in Full Text gives 247 result(s) in Beilstein Journal of Organic Chemistry. Showing first 200.
Synthesis of benzannelated sultams by intramolecular Pd-catalyzed arylation of tertiary sulfonamides
Beilstein J. Org. Chem. 2017, 13, 1932–1939, doi:10.3762/bjoc.13.187
- latter transformation was a rhodium octanoate-catalyzed intramolecular carbenoid insertion into an ortho CAr–H bond (Scheme 1) [21][22], which proceeded with good yields in most cases. However, with non-equivalent aryl ortho-positions in the starting diazo compounds, mixtures of regioisomers – virtually
Accessing simply-substituted 4-hydroxytetrahydroisoquinolines via Pomeranz–Fritsch–Bobbitt reaction with non-activated and moderately-activated systems
Beilstein J. Org. Chem. 2017, 13, 1871–1878, doi:10.3762/bjoc.13.182
- - and the ortho-position to the substituent, as expected, the para-position predominated and the 7-substituted THIQs (e.g., 10e–g, Scheme 4) were obtained as the major product. Nevertheless, it was possible to isolate a usable amount of the 5-substituted THIQ 14e. The ratio of the two regioisomers
1-Imidoalkylphosphonium salts with modulated Cα–P+ bond strength: synthesis and application as new active α-imidoalkylating agents
Beilstein J. Org. Chem. 2017, 13, 1446–1455, doi:10.3762/bjoc.13.142
- 3). The imidoalkylation of anisole and toluene gave the expected products as mixtures of ortho and para isomers in molar ratios ranging from 1.4:1.0 to 1.0:4.0 (Table 3). It seems that the steric congestion is the main factor governing the molar ratio of the regioisomers. Thus an excess of ortho
Switchable highly regioselective synthesis of 3,4-dihydroquinoxalin-2(1H)ones from o-phenylenediamines and aroylpyruvates
Beilstein J. Org. Chem. 2017, 13, 1350–1360, doi:10.3762/bjoc.13.132
- acid) which we studied. Six regioisomeric 3,4-dihydroquinoxalin-2(1H)-one pairs were selectively prepared and characterised. Based on our experiences, a simplified methodology for determining the structure of the regioisomers was proposed. We developed two general and highly selective methodologies
- when choosing the most optimal reaction conditions for the synthesis of the desired 3,4-dihydroquinoxalin-2(1H)-one regioisomers with the best selectivity. The demonstrated methodologies in this article may also be applied to differently substituted 3,4-dihydroquinoxalin-2(1H)-ones in general, which
- monosubstituted o-phenylenediamines 11. In this case the amino groups usually have different reactivity and thus produce a mixture of regioisomeric products. If both regioisomers are needed, one can separate them [21]. Separation can be difficult to such an extent that some of the Cu(II) chelators were
Synthesis of novel 13α-estrone derivatives by Sonogashira coupling as potential 17β-HSD1 inhibitors
Beilstein J. Org. Chem. 2017, 13, 1303–1309, doi:10.3762/bjoc.13.126
- 10.3762/bjoc.13.126 Abstract Novel 13α-estrone derivatives were synthesized by Sonogashira coupling. Transformations of 2- or 4-iodo regioisomers of 13α-estrone and its 3-methyl ether were carried out under different conditions in a microwave reactor. The 2-iodo isomers were reacted with para-substituted
- compounds. All the halogenated 3-hydroxy and the 4-substituted regioisomers of 3-methyl ethers displayed substantial inhibitory activity against the 17β-hydroxysteroid dehydrogenase type 1 enzyme (17β-HSD1). Certain derivatives displayed a similar or more pronounced effect than those of their parent
- -catalyzed C–C coupling reactions. Some Sonogashira couplings on estrane, but not on the 13α-estrane core have been performed at C-2, -3, -11, -16 and -17. To the best of our knowledge, 4-coupled regioisomers have not been synthesized to date [19]. Couplings of steroidal alkynes with small molecular halides
Regioselective (thio)carbamoylation of 2,7-di-tert-butylpyrene at the 1-position with iso(thio)cyanates
Beilstein J. Org. Chem. 2017, 13, 1032–1038, doi:10.3762/bjoc.13.102
- min, 1,8-bis-carbothioamide 4, containing ≈20% of other regioisomers (9%) and nitrile 5 (7%) were isolated by column chromatography besides the expected 3o (78%). The amounts of 4 and 5 significantly increased along with the reaction time (Table 1). The highest yield of 4 (33%) was found after 6 h
Metal-free hydroarylation of the side chain carbon–carbon double bond of 5-(2-arylethenyl)-3-aryl-1,2,4-oxadiazoles in triflic acid
Beilstein J. Org. Chem. 2017, 13, 883–894, doi:10.3762/bjoc.13.89
- , entry 7), chlorobenzene (2b + 2c, Table 2, entry 6 and 2q + 2r, entry 21), and toluene (2u + 2v, Table 2, entry 24). The exact structures of these regioisomers were determined on the basis of multiplet signals of the aromatic protons in the 1H NMR spectra. The observation of regioisomeric products
Ultrasound-promoted organocatalytic enamine–azide [3 + 2] cycloaddition reactions for the synthesis of ((arylselanyl)phenyl-1H-1,2,3-triazol-4-yl)ketones
Beilstein J. Org. Chem. 2017, 13, 694–702, doi:10.3762/bjoc.13.68
- as a mixture of regioisomers (6:1) (Table 2, entry 10). In addition, the possibility to perform the reaction of 2-azidophenyl phenyl selenide (1a) with β-keto-esters, β-keto-amides and α-cyano-ketones 2f–k was also investigated. The reaction conditions optimized for 1,3-diketone 2a were employed, but
Isoxazole derivatives as new nitric oxide elicitors in plants
Beilstein J. Org. Chem. 2017, 13, 659–664, doi:10.3762/bjoc.13.65
- the yields of isoxazole products are quite low because of side reactions and both regioisomers are generally obtained [23][24][25]. The one-pot 1,3-dipolar cycloaddition reaction of a nitrile oxide, generated in situ from the corresponding hydroxymoyl chloride, with an in situ brominated electron
Synthesis of 1-indanones with a broad range of biological activity
Beilstein J. Org. Chem. 2017, 13, 451–494, doi:10.3762/bjoc.13.48
- ] cyclotrimerization of the dialkyne 306 with variously disubstituted alkynes 307 performed on a solid phase TentaGel® resin (0.25 mmol/g) in the presence of Ru catalyst (Scheme 86). In case of 309–316, this reaction led to the formation of mixtures of two regioisomers. The examined regioisomeric ratios (a/b) were
- ranged from 1:2 to 2:3 with a preference to 310a–315a regioisomers. An interesting approach to the synthesis of 1-indanones and 1-indenones is based on the hexadehydro-Diels–Alder (HDDA) reaction in which an alkyne reacts in the [4 + 2] cycloaddition with diyne and forms a reactive benzyne species as a
Brønsted acid-mediated cyclization–dehydrosulfonylation/reduction sequences: An easy access to pyrazinoisoquinolines and pyridopyrazines
Beilstein J. Org. Chem. 2017, 13, 428–440, doi:10.3762/bjoc.13.46
- phenyl group was proposed to introduce at the 3-position in substituted pyrazinone via regioselective bromination followed by Suzuki coupling with phenylboronic acid. Accordingly, the bromination of 10a was successfully carried out to furnish regioisomers 12a and 12b in 82% yield upon treatment with
- bromodimethylsulfonium bromide (BDMS) [38] in dichloromethane at 0 °C to room temperature. The conventional Suzuki coupling of the regioisomers 12a and 12b with phenylboronic acid furnished the corresponding arylated products 13a and 13b in excellent yield (Scheme 5). To our dismay, the imide 7h did not participate in
- reaction mixture was purified through silica gel column chromatography using ethyl acetate/hexane, 30:70 as eluent to afford 12a and 12b in the ratio 79:21. The regioisomers of bromopyrazinone (12a and 12b) (1.0 mmol), bis(triphenylphosphine)palladium(II) chloride (10 mol %, 7 mg) in dimethylformamide (2
Revaluation of biomass-derived furfuryl alcohol derivatives for the synthesis of carbocyclic nucleoside phosphonate analogues
Beilstein J. Org. Chem. 2017, 13, 251–256, doi:10.3762/bjoc.13.28
- treatment with Boc2O afforded the suitable heterocyclic precursor 17 (Scheme 4). The coupling reaction of (+/−)-7 and 17 using the Mitsunobu reaction gave a separable mixture of N9/N7 regioisomers (+/−)-18 and (+/−)-19 with 55% and 5% yield, respectively. After purification, compound (+/−)-18 was treated
Silyl-protective groups influencing the reactivity and selectivity in glycosylations
Beilstein J. Org. Chem. 2017, 13, 93–105, doi:10.3762/bjoc.13.12
- exclusively at the equatorial 4-OH group presumably due to the bulkiness of the silylated donor. Thus compound 55 (Scheme 9) was formed as the only product out of four possible isomers in 54% yield. When the D-gluco-configured acceptor analogue of 54 was used, a mixture of regioisomers was obtained. However
Multicomponent synthesis of spiropyrrolidine analogues derived from vinylindole/indazole by a 1,3-dipolar cycloaddition reaction
Beilstein J. Org. Chem. 2016, 12, 2893–2897, doi:10.3762/bjoc.12.288
- -alkylindole and indazole derivatives 2 that can be obtained from 5-bromoindoles/indazoles (1). The latter compounds were synthesized according to procedures described in the literature [18][19][20]. The regioisomers of N-alkylated 5-bromoindazoles were isolated by column chromatography using a hexane–ethyl
- indazole analogues 7e–k under similar reaction conditions. Based on the same logic of vinylindole, regioisomers of N-alkylvinylindazole were considered. So, this 1,3-dipolar cycloaddition reaction could be well applied to both derivatives which afforded a range of differentially substituted final products
cis-Diastereoselective synthesis of chroman-fused tetralins as B-ring-modified analogues of brazilin
Beilstein J. Org. Chem. 2016, 12, 2816–2822, doi:10.3762/bjoc.12.280
- –n leading to (±)-5b–n. Reaction conditions: (±)-6b–h (0.4 mmol), TsOH·H2O (20 mol %), toluene (8 mL), 80 °C, 45 min. The numbers in parentheses represent isolated yields after silica gel column chromatography. aYield of isolated mixture of the inseparable regioisomers. ORTEP diagram of 5k
Enzymatic synthesis and phosphorolysis of 4(2)-thioxo- and 6(5)-azapyrimidine nucleosides by E. coli nucleoside phosphorylases
Beilstein J. Org. Chem. 2016, 12, 2588–2601, doi:10.3762/bjoc.12.254
- -thiouridine (very weak substrate) vs uridine (non-substrate), thymidine (very weak substrate) vs 2-thiothymidine (non-substrate). Shugar and co-workers studied the substrate properties of N-3-regioisomers of adenosine and inosine, N3-(β-D-ribofuranosyl)-adenine (N3-Ado) and -hypoxanthine (N3-Ino
- the PNPs. Noteworthy that phosphorolysis of both N-3-regioisomers proceeds irreversibly. In the present work, we compared the energy minimized structures of N3-Ado and 5-aza-2'-deoxycytidine (14) and found a rather similar stereochemistry of both structures, in particular, a quite similar orientation
Facile synthesis of a 3-deazaadenosine phosphoramidite for RNA solid-phase synthesis
Beilstein J. Org. Chem. 2016, 12, 2556–2562, doi:10.3762/bjoc.12.250
- through celite and partitioned between dichloromethane and 5% aqueous sodium bicarbonate solution (10 mL each). The organic layer was washed twice with 5% aqueous sodium bicarbonate solution (2 × 10 mL), dried over Na2SO4 and evaporated. The regioisomers were separated by flash chromatography (toluene
Biomimetic synthesis and HPLC–ECD analysis of the isomers of dracocephins A and B
Beilstein J. Org. Chem. 2016, 12, 2523–2534, doi:10.3762/bjoc.12.247
- by preparative HPLC to result in regioisomers (±)-2a–d and (±)-3a–d as crystalline powders in a ratio of 43:57, respectively. These data clearly showed that the reaction took place without notable regioselectivity, which was in agreement with the observed 58:42 ratio of natural dracocephins A and B
Combined experimental and theoretical studies of regio- and stereoselectivity in reactions of β-isoxazolyl- and β-imidazolyl enamines with nitrile oxides
Beilstein J. Org. Chem. 2016, 12, 2390–2401, doi:10.3762/bjoc.12.233
- challenge. We turned our attention to the reaction of enamines with nitrile oxides (or their precursors, hydroxamoyl chlorides). The reaction has been shown to take place regioselectively to form only one of two possible regioisomers [18][19][20][21][22][23][24][25][26]. Therefore, this holds some promise
- around the double bond, and found to be 38.09 kcal∙mol−1 above 1a_1 in free energy. Calculations of the suggested mechanisms (Scheme 3) performed for E-isomer 1a_1 and nitrile oxide 6a allowed localizing a concerted transition state for both, observed and not observed regioisomers 3 and 8, respectively
Palladium-catalyzed ring-opening reactions of cyclopropanated 7-oxabenzonorbornadiene with alcohols
Beilstein J. Org. Chem. 2016, 12, 2189–2196, doi:10.3762/bjoc.12.209
- the C1 position, the formation of two regioisomers is possible (Scheme 4). The bridgehead-oxygen bond can break in two different directions (a or b), creating either a tertiary or secondary cation which after the nucleophilic ring opening creates two different regioisomers. In all cases, the
- cyclopropanated 8 and its proposed ring-opening mechanisms. Formation of the possible regioisomers for the ring opening of asymmetric C1-substituted cyclopropanated oxabenzonorbornadiene. Effects of palladium catalysts and catalyst equivalency on the ring-opening reaction of oxabicyclic alkene 8a with alcohols
Comparing blends and blocks: Synthesis of partially fluorinated diblock polythiophene copolymers to investigate the thermal stability of optical and morphological properties
Beilstein J. Org. Chem. 2016, 12, 2150–2163, doi:10.3762/bjoc.12.205
- -fluorinated monomer gives an approximate 4:1 mixture of regioisomers [45][46]. Although this mixture of isomers can afford good regularity under certain conditions, it can be expected to have a detrimental effect on regioregularity [47]. For this reason most block co-polymers utilize a regiochemically pure
Stereo- and regioselectivity of the hetero-Diels–Alder reaction of nitroso derivatives with conjugated dienes
Beilstein J. Org. Chem. 2016, 12, 1949–1980, doi:10.3762/bjoc.12.184
- -heteroarene reactants [91]. Nicholas and co-workers investigated the thermal (uncatalyzed) and Cu(I)-catalyzed reactions of 2-nitrosopyridine with various dienes [92]. Generally, the cycloaddition of an unsymmetrical diene and nitroso compound will lead to two regioisomers – proximal and distal (Scheme 11
- dichloromethane throughout. When the reaction in solution shown in Scheme 20, giving 1,2-oxazine 97, was performed in MeOH, the ratio of regioisomers was changed from 3:2 (in DCM) to 3:1 (in MeOH) [100]. The comparison between the solution and solid-phase syntheses is possible to do with respect to the
- regioselectivity. On the other hand, its isomer 106 gave two regioisomers in a ratio of 2:1 [88][95] (Scheme 21). This was proposed to be due to an increased steric interaction between the phenyl ring at position 4 on the β-lactam ring in 107 and the nitrosobenzene (47) during the formation of product 108. For the
Synthesis of pyrrolo[2,1-f][1,2,4]triazin-4(3H)-ones: Rearrangement of pyrrolo[1,2-d][1,3,4]oxadiazines and regioselective intramolecular cyclization of 1,2-biscarbamoyl-substituted 1H-pyrroles
Beilstein J. Org. Chem. 2016, 12, 1780–1787, doi:10.3762/bjoc.12.168
- in low yields (40% combined yield, entry 3, Table 1). Alternatively, when 2.5 equivalents of Et3N were used, the two regioisomers 11a and 12a were obtained in an excellent overall yield of 87% (entry 2, Table 1). In addition, the ratio of 11a to 12a was not significantly affected by reaction times
- and temperatures (entries 4–6, Table 1). Although initial attempts to synthesize pyrrolotriazinone 12a regioselectively were not successful, it should be highlighted that the regioisomers oxadiazine 11a and triazinone 12a could be easily prepared under very mild conditions (0 °C for 5 min), whereas
- and triazinones 12 are non-crystalline, their exact structures were assigned by NMR spectroscopy (1H and 13C). With the literature results alone [9][10][11][12] the identity of the regioisomers could not be accurately confirmed; therefore, the NMR studies were required. As shown in Table 4, different
Rearrangements of organic peroxides and related processes
Beilstein J. Org. Chem. 2016, 12, 1647–1748, doi:10.3762/bjoc.12.162
Catalytic Chan–Lam coupling using a ‘tube-in-tube’ reactor to deliver molecular oxygen as an oxidant
Beilstein J. Org. Chem. 2016, 12, 1598–1607, doi:10.3762/bjoc.12.156
- several examples of literature reported cases where mixtures of regioisomers had been obtained were wrongly assigned. The process described does have certain limitations. For certain nucleophilic substrates no products were obtained when C–N coupling with 4-methoxyphenylboronic acid (17) was attempted
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