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Search for "cis" in Full Text gives 701 result(s) in Beilstein Journal of Organic Chemistry. Showing first 200.
Synthesis of novel fluorinated building blocks via halofluorination and related reactions
Beilstein J. Org. Chem. 2020, 16, 2562–2575, doi:10.3762/bjoc.16.208
- ). Our experiments were continued with compound 4, the cis isomer of the diester (rac)-1. In this case, two different halonium ion intermediates can be formed, leading to the possible products (rac)-5a,b and (rac)-6a,b (Scheme 3). Since the axial ester group somewhat hinders the attack of the large
- -Fluor®, CH2Cl2, 0 °C to rt, 27 h, 61% yield of two isomeric bromofluorinated products in a ≈11:10 ratio). We continued our synthetic explorations with unsaturated fused ring systems. Our first choice was the easily accessible N-benzylated cis-tetrahydrophthalic imide 7. Unfortunately, both bromo- and
- iodofluorination of 7 yielded a mixture of two isomeric halofluorinated products for which the separation failed (Scheme 5). Since halofluorinations of the trans-diester (rac)-1 proceeded more selectively than analogous reactions of the stereoisomeric cis-diester 4, it seemed reasonable to prepare the N-benzylated
NMR Spectroscopy of supramolecular chemistry on protein surfaces
Beilstein J. Org. Chem. 2020, 16, 2505–2522, doi:10.3762/bjoc.16.203
- observed the binding of multiple tweezers to the same protein [7][80], which results in a shifting and broadening of many signals in the 1H,15N-HSQC, but the tweezers were not able to bind to all Lys and Arg residues on the protein surface. The titration of tweezers to the human peptidyl prolyl cis-trans
Formation of an exceptionally stable ketene during phototransformations of bicyclo[2.2.2]oct-5-en-2-ones having mixed chromophores
Beilstein J. Org. Chem. 2020, 16, 2297–2303, doi:10.3762/bjoc.16.190
- photoreactions of bridged bicyclic systems like 3a–g were carried out [9][10][11][12][13]. These molecules contain a δ-keto-α,β-enone system juxtaposed with a (cis)-dibenzoylalkene moiety. Interestingly, photoreactions of 3a–f were found to follow regioselective photoindiuced 1,5-phenyl migration from the more
- proximate oxygen is a general reaction route for (cis)-dibenzoylalkene chromophores [19][20][21][22]. In unsymmetrical derivatives such migrations have been found to take place from the benzoyl group attached to the more crowded olefinic carbon atom to the less crowded one [23]. A similar observation has
- -requirement of any sensitizer in the process indicates that the reaction presumably proceeds via a triplet-mediated pathway. Moreover, the non-appearence of any 1,2-AS product signifies that the β,γ-enone part is inactive. On the other hand (cis)-dibenzoylalkene like α,β-enone part of such multichromophoric
The B & B approach: Ball-milling conjugation of dextran with phenylboronic acid (PBA)-functionalized BODIPY
Beilstein J. Org. Chem. 2020, 16, 2272–2281, doi:10.3762/bjoc.16.188
- related esters are relevant synthetic building blocks widely employed as cross-coupling reagents [14] as well as protecting groups for polyols and diamines [15][16]. Moreover, the reversible covalent interaction of boronic acids with specifically oriented cis-1,2 and 1,3-diols has been successfully
Regioselective cobalt(II)-catalyzed [2 + 3] cycloaddition reaction of fluoroalkylated alkynes with 2-formylphenylboronic acids: easy access to 2-fluoroalkylated indenols
Beilstein J. Org. Chem. 2020, 16, 2193–2200, doi:10.3762/bjoc.16.184
- products 3aA and 4aA in 76% yield as a regioisomeric 66:34 mixture (Table 1, entry 1). Intriguingly, a small amount of the undesired trans-3-fluoroalkylated indanone 5aA was obtained as a side product, whereas the cis-3-fluoroalkylated and cis/trans-2-fluoroalkylated indanones were not observed. As shown
- , and previous results showed that the J value of the nonfluoroalkylated trans-2,3-disubstituted indanone 8 is 5.0 Hz, whereas the J value of the cis-isomer 9 is 8.0 Hz [37]. The proposed catalytic cycles for the cobalt-catalyzed [2 + 3] cycloaddition process leading to 2-fluoroalkylated indenols and 3
Photosensitized direct C–H fluorination and trifluoromethylation in organic synthesis
Beilstein J. Org. Chem. 2020, 16, 2151–2192, doi:10.3762/bjoc.16.183
Lipophilicity trends upon fluorination of isopropyl, cyclopropyl and 3-oxetanyl groups
Beilstein J. Org. Chem. 2020, 16, 2141–2150, doi:10.3762/bjoc.16.182
- ). With one (A4) and two (A5) trifluoromethyl groups, large increases in lipophilicity are observed. An interesting series (B) of phenylcyclopropanes was reported by O’Hagan [25][26]. All-cis vicinal trifluorination as in B2 led to a significant reduction in lipophilicity compared to the nonfluorinated B1
- decrease seen for E2 is in accord with the observations for the β-fluorinated analogues of 7a and 7c (see above, Figure 2). The cis-isomer E3 has a slightly lower lipophilicity than the trans-isomer E4. The lower lipophilicity decrease upon monofluorination in series E compared to series F could be related
Azo-dimethylaminopyridine-functionalized Ni(II)-porphyrin as a photoswitchable nucleophilic catalyst
Beilstein J. Org. Chem. 2020, 16, 2119–2126, doi:10.3762/bjoc.16.179
- Abstract We present the synthesis and the photochemical and catalytic switching properties of an azopyridine as a photoswitchable ligand, covalently attached to a Ni(II)-porphyrin. Upon irradiation with 530 nm (green light), the azopyridine switches to the cis configuration and coordinates with the Ni2
- shielded in the cis configuration and therefore catalytically inactive. The basicity was restored by isomerization to the trans state leading to a rapid conversion to the β-nitroalcohol, the product of the Henry reaction [10][11][12]. We now present a photoswitchable catalyst whose basicity is controlled
- ][19][20][21][22][23][24][25][26]. In the present study, the basicity change linked to the coordination/decoordination process is explored. If the azo substituent is in cis configuration, the lone pair of the pyridine unit coordinates to the central Ni2+ ion, reducing the nucleophilic power and the
Reactions of 3-aryl-1-(trifluoromethyl)prop-2-yn-1-iminium salts with 1,3-dienes and styrenes
Beilstein J. Org. Chem. 2020, 16, 2064–2072, doi:10.3762/bjoc.16.173
- extent (13c) or not at all (13b) (Scheme 4). A remarkable stereochemical aspect accompanied the reaction of 1a with (E)-1-phenyl-1-propene leading to 2-((E)-1-phenylprop-1-enyl)indene 12d, where trans(Ph,Me)→cis isomerization at the olefinic bond has occurred. The E-configuration was assigned based on
- with the expected orientation of the cycloaddition. Cis-annelated cyclobutene 18 (1H NMR: 3JH,H = 3.8 Hz for the angular protons) and the iminium-substituted primary cycloadduct are not expected to undergo a fast ring opening under moderate thermal conditions, because the orbital-symmetry-allowed
- concerted conrotatory process [47][48] would create a strained cis,trans-dihydrobenzo[8]annulene ring system. Cyclobutenes resulting from a [2 + 2] cycloaddition of electrophilic alkynes and alkenes under moderate thermal conditions have been isolated also from the reaction of CF3-free propyniminium salts
Syntheses of spliceostatins and thailanstatins: a review
Beilstein J. Org. Chem. 2020, 16, 1991–2006, doi:10.3762/bjoc.16.166
- compounds. These compounds generally contain 9 stereocenters spread over a common (2Z,4S)-4-acetoxy-2-butenamide fragment, an (all-cis)-2,3,5,6-tetrasubstituted tetrahydropyran fragment and a terminal oxane ring joined by a dienyl chain. Due to the impressive antitumor properties of these compounds, along
- all contain a common (2Z,4S)-4-acetoxy-2-butenamide fragment (in green, Figure 1), appended to an (all-cis)-2,3,5,6-tetrasubstituted tetrahydropyran fragment (in red, Figure 1). The members of this family primarily differ with respect to the terminal oxane ring (in blue, Figure 1) which is attached to
- asymmetric synthesis of a (Z)-2-hydroxy-3-pentene unit, with most proceeding via the cis-reduction of 4-acetoxy-2-pentynoic acid (13). The synthesis by Kitahara et al. [8][9] is the exception, where the chiral center is derived from relatively inexpensive (S)-ethyl lactate (14). This was transformed into the
Selective preparation of tetrasubstituted fluoroalkenes by fluorine-directed oxetane ring-opening reactions
Beilstein J. Org. Chem. 2020, 16, 1936–1946, doi:10.3762/bjoc.16.160
- analysis (see Supporting Information File 1). The attack of the bromide ion this time occurred from the side of the alkene hydrogen atom (cis attack) and away from the bulky phthalimido group giving solely product E-4d. Likewise, the reaction of the alkyl-substituted substrate 5 proceeded with excellent E
Polarity effects in 4-fluoro- and 4-(trifluoromethyl)prolines
Beilstein J. Org. Chem. 2020, 16, 1837–1852, doi:10.3762/bjoc.16.151
- C4-exo conformation of the pyrrolidine ring. Keywords: amino acids; cis–trans isomerism; fluorine; polarity; proline; Introduction Polarity is among the key features essential for understanding the behavior of organic molecules of biological origin. In particular, there is a set of polarity-related
- experimental 2-CH multiplicity with the one predicted for the pure conformers (Figure 4). As can be seen from the data, both fluoroprolines exhibited stabilization of certain side-chain conformers: the cis-isomer 1 stabilized the C4-endo envelope, whereas the trans-isomer 2 stabilized the C4-exo (Figure 5
- analogues, 3 and 4. However, the effect was not entirely clean. For example, in the cis-isomer 3, the exo-C4 envelope was only preferred in the major amide rotamer, whereas in the minor one, a mixture of two envelopes was observed. In the trans-isomer 4, the C4-endo envelope was found in all cases, except
Synthesis and highly efficient light-induced rearrangements of diphenylmethylene(2-benzo[b]thienyl)fulgides and fulgimides
Beilstein J. Org. Chem. 2020, 16, 1820–1829, doi:10.3762/bjoc.16.149
- -yl)-9-phenyl-3a,4-dihydronaphtho[2,3-c]furan-1,3-dione with cis-configuration of hydrogen atoms C(4)H and C(5)H. Two doublet signals of these protons at 4.49 and 5.37 ppm with characteristic spin–spin coupling constant J = 7.3 Hz are observed in the 1H NMR spectrum [24]. The photoinduced
- rearrangement 9C comprises alternating molecules of two enantiomers cis-9C and cis-9C’ corresponding to a racemic compound. The structure of cis-9C’ is shown in Figure 5. The dihydrobenzene cycle С(3)С(4)С(5)С(16)С(15)С(14) of cis-9C’ is nonplanar with inflections along the lines C(3)...C(16) and C(4)...C(16
- ) at 15.0° and 44.4°, respectively. The C(4)–C(5) bond (its length is equal to 1.535(3) Å) is significantly elongated compared to the double C(4)–C(5) bond of 3Z (1.360(2) Å). The list of other bond lengths and valence angles of cis-9C’ is presented in Table S3 (Supporting Information File 1
One-pot synthesis of oxazolidinones and five-membered cyclic carbonates from epoxides and chlorosulfonyl isocyanate: theoretical evidence for an asynchronous concerted pathway
Beilstein J. Org. Chem. 2020, 16, 1805–1819, doi:10.3762/bjoc.16.148
- in ratios close to 1:1 as shown in Table 2. trans-Stilbene (7d) and cis-stilbene epoxids (7e) in the presence of CSI gave trans-4,5-diphenyl-1,3-dioxolan-2-one (8d), trans-4,5-diphenyloxazolidin-2-one (9d) and cis-4,5-diphenyl-1,3-dioxolan-2-one (8e), cis-4,5-diphenyloxazolidin-2-one (9e
Synthesis of Streptococcus pneumoniae serotype 9V oligosaccharide antigens
Beilstein J. Org. Chem. 2020, 16, 1693–1699, doi:10.3762/bjoc.16.140
- pentasaccharide RU with glucuronic acid at the non-reducing end. Results and Discussion The SP 9V linear pentasaccharide RU 1 contains ᴅ-glucuronic acid (ᴅ-GlcpA), ᴅ-galactose (ᴅ-Galp), 2-acetamido-2-deoxy-ᴅ-mannose (ᴅ-ManpNAc), and ᴅ-glucose (ᴅ-Glcp) units. Several cis glycosidic linkages, including a β
Pauson–Khand reaction of fluorinated compounds
Beilstein J. Org. Chem. 2020, 16, 1662–1682, doi:10.3762/bjoc.16.138
- affording the corresponding CF3-containing dehydropiperidine derivatives in excellent yields. Additionally, enynes 22 and 23 were evaluated as substrates in the intramolecular PKR, yielding the corresponding CF3-containing heterobicyclic derivatives in 68% (85:15 ratio of trans/cis stereoisomers) and 80
- % yield (18:82 ratio of trans/cis stereoisomers), respectively (Scheme 10). Ichikawa and co-workers described an attractive route to synthesize pyrrolidine ring-fused fluorinated cyclopentenone analogs via intramolecular PKR starting from 2-bromo-3,3,3-trifluoroprop-1-ene [50][51]. To this end, N
- allyl ether 32a afforded the corresponding cis bicyclic product 33a in moderate yield and high diastereoselectivity (dr > 20:1). Other fluorinated allyl propargyl ethers 32b–d afforded the corresponding bicyclic PK-adducts 33 in moderate chemical yields but with high cis-selectivity. On the other hand
Fluorohydration of alkynes via I(I)/I(III) catalysis
Beilstein J. Org. Chem. 2020, 16, 1627–1635, doi:10.3762/bjoc.16.135
- established by single crystal X-ray diffraction (Figure 2). Interestingly, a study by Pattison has established that α-fluoroketones preferentially adopt a cis-conformation in polar solvents [54]. In the solid state, a dihedral angle of φ = −3.7° was observed thereby placing the C–F bond in the same plane as
Synthesis of new dihydroberberine and tetrahydroberberine analogues and evaluation of their antiproliferative activity on NCI-H1975 cells
Beilstein J. Org. Chem. 2020, 16, 1606–1616, doi:10.3762/bjoc.16.133
- of THBERs 3a chosen as representative example, reveals that these two hydrogens are in cis position (Figure 4). Therefore, the THBERs 3 show the same configuration of the metabolite cavidine that is the 13-methyltetrahydroprotoberberine alkaloid which occur in various species of Corydalis [69
Heterogeneous photocatalysis in flow chemical reactors
Beilstein J. Org. Chem. 2020, 16, 1495–1549, doi:10.3762/bjoc.16.125
One-step route to tricyclic fused 1,2,3,4-tetrahydroisoquinoline systems via the Castagnoli–Cushman protocol
Beilstein J. Org. Chem. 2020, 16, 1456–1464, doi:10.3762/bjoc.16.121
- chromatography to give the individual diastereomers. The acid (−)-trans-22 and its methyl ester are known compounds, which were prepared by an independent method [35]. NOESY experiments were used to examine the stereochemical assignments in compounds 21–24. The cis diastereomers 22–24 showed distinct NOE cross
- -signals between protons H-1 and H-11b, and for cis-21 – between H-1 and H-10b. No such NOE peaks were identified in the spectra of the trans isomers (Figure 2). Further, the assignment of the relative configuration of the products 22–24 was supported by the vicinal coupling constants 3J1,11b for H-1 and H
- -11b. The 1H NMR spectra of the trans diastereomers were expected to display a larger coupling constant 3J1,11b in comparison with the spectra of the corresponding cis analogs [36]. A similar difference was observed in the spectra of the diastereomeric dibenzo[a,g]quinolizidinone compounds as well [14
An overview on disulfide-catalyzed and -cocatalyzed photoreactions
Beilstein J. Org. Chem. 2020, 16, 1418–1435, doi:10.3762/bjoc.16.118
- . In 1996, Burton and co-workers reported the stereoselective synthesis of cis-1,2-difluorotriethylsilyethylene and its conversion to a variety of cis-1,2-difluoroethylene synthons, which are important building blocks in the preparation of fluorine-containing pharmaceuticals, polymers, and bioactive
- compounds. In the synthesis of these synthons, the key transformation, the isomerization of the trans-1,2-difluorotriethylsilylethylene 57 to the cis isomer 58, is realized with phenyl disulfide under ultraviolet-light irradiation (Scheme 22) [29]. In 2009, Tsuboi and co-workers also reported a dendrimer
Recent synthesis of thietanes
Beilstein J. Org. Chem. 2020, 16, 1357–1410, doi:10.3762/bjoc.16.116
- nm or 589 nm UV light gave the desired thietanes 190–195 with retention of the olefin configuration in most cases. An exception was observed for the reaction of 184a with (Z)-prop-1-enylbenzene [(Z)-185], which generated a mixture of cis- and trans-thietanes, cis-190 and trans-190, both configuration
- ) reacted with electron-poor olefins, such as acrylonitrile (187b), methyl acrylate (187c), and cis- and trans-1,2-dichloroethenes 188, under photochemical conditions, giving 2-silylthietanes 317 and 318 in a regio- and highly stereoselective manner. However, silyl thietanes without any regio- or
Synthesis of 3-substituted isoxazolidin-4-ols using hydroboration–oxidation reactions of 4,5-unsubstituted 2,3-dihydroisoxazoles
Beilstein J. Org. Chem. 2020, 16, 1313–1319, doi:10.3762/bjoc.16.112
- of N/O-containing heterocycles used as the key intermediates in the synthesis of more complex cyclic and acyclic compounds, including various biologically active molecules. Here, we present a fast and highly stereoselective approach towards both C-3/4-cis and C-3/4-trans isomers of 3-substituted
- hydroxylamines using malonoyl peroxide, providing N-tosylated 3-aryl-substituted 4-hydroxyisoxazolidines in a highly stereoselective manner in favor of the C-3/4-trans isomers [27]. We believe that the 3-substituted isoxazolidin-4-ols, represented by the general structures of the trans and the cis stereoisomer 3
- side, which is opposite relatively to the phenyl substituent at the C-3 carbon. The proposed C-3/4-trans relative configuration was confirmed by NOESY 1D experiments for 8a (Figure 2), and the results obtained were later compared with those measured for the respective C-3/4-cis isomer. For 8a, the
Ferrocenyl-substituted tetrahydrothiophenes via formal [3 + 2]-cycloaddition reactions of ferrocenyl thioketones with donor–acceptor cyclopropanes
Beilstein J. Org. Chem. 2020, 16, 1288–1295, doi:10.3762/bjoc.16.109
- -arylcyclopropane dicarboxylates reacted with the corresponding aryl ferrocenyl thioketones in a completely diastereoselective manner to form single products in which (C-2)-Ar and (C-5)-ferrocenyl groups were oriented in a cis-fashion. In contrast, the same cyclopropanes underwent reaction with alkyl ferrocenyl
- were formed with complete diastereoselectivity, leading to a single isomer. In order to establish the structure of the isomers, a single crystal obtained for compound 9c was studied by X-ray diffraction analysis which showed, that the Ph(C-2) group and Fc(C-5) substituent were mutually cis-oriented
- were trans-oriented and for that reason, this isomer was described as trans-9d (Figure 1). Analogously, the reaction of ferrocenyl n-propyl thioketone (8e) with 5a led to a 52:48 mixture of trans- and cis-isomers of 9e, which were isolated in a total yield of 97% and identified without further
A simple and easy to perform synthetic route to functionalized thienyl bicyclo[3.2.1]octadienes
Beilstein J. Org. Chem. 2020, 16, 1092–1099, doi:10.3762/bjoc.16.96
- derivatives 3–7 as mixtures of cis and trans-isomers. The isomers of compounds 3 and 4 were separated by column chromatography and completely spectroscopically characterized, while in the case of compounds 5–7, only trans-isomers were obtained. Figure 3 presents parts of the 1H NMR spectra of the trans
- shifts of the aromatic protons could be observed, with the proton chemical shift shifting upfield. The comparison of the UV spectra of the cis- and trans-isomers of compound 3 (Figure 4) showed the expected bathochromic and hyperchromic shifts of the trans-isomers, due to the planarity of the structure
- [3.2.1]octadiene derivatives by irradiating the toluene solution of compound's 3–7 mixture of cis- and trans-isomers in the presence of iodine (Scheme 2 and Scheme 3). The electrocyclization reactions were successfully implemented in most cases and photoproducts 8–11 were obtained in moderate yields. The
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