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Search for "nitrone" in Full Text gives 29 result(s) in Beilstein Journal of Organic Chemistry.
Exploring the role of halogen bonding in iodonium ylides: insights into unexpected reactivity and reaction control
Beilstein J. Org. Chem. 2023, 19, 1171–1190, doi:10.3762/bjoc.19.86
- ]. The authors discounted a free carbene-based C–H insertion because conducting the reaction in the presence of the radical trap phenyl N-tert-butyl nitrone (PBN) and the radical scavenger TEMPO resulted in decreased yields and isolation of their iodonium ylide adducts. Additional kinetic isotope effect
Highly stereocontrolled total synthesis of racemic codonopsinol B through isoxazolidine-4,5-diol vinylation
Beilstein J. Org. Chem. 2021, 17, 2781–2786, doi:10.3762/bjoc.17.188
- first prepared synthetically before its isolation from natural crude material, employing a stereoselective addition of an aryl Grignard reagent to a five-membered chiral cyclic nitrone derived from ᴅ-arabinose [2]. Its analytical data were consistent with those for the later isolated natural product
Recent progress in the synthesis of homotropane alkaloids adaline, euphococcinine and N-methyleuphococcinine
Beilstein J. Org. Chem. 2021, 17, 28–41, doi:10.3762/bjoc.17.4
- % overall yields. A relevant consideration in Holmes’s synthesis is: the nitrone is the same common intermediate as Gössinger’s [25], which is cyclized to form the tricyclic adducts. While the Gössinger route started from the cyclic 1-hydroxypiperidine, Holmes performed in situ cyclization to prepare the
- nitrone. Murahashi synthesis – 2000 Starting from secondary amines, Murahashi et al. developed a method for preparing homochiral β-sulfinyl nitrones [41]. Accordingly, (+)-euphococcinine (2) was prepared through allylation followed by the 1,3-dipolar cycloaddition of β-sulfinyl nitrone 20 derived from
- provide β-sulfinyl hydroxylamine 19 in a diastereoisomeric ratio of 67:33 in 52% yield. Oxidation of 19 to nitrone 20 occurred chemoselectivelly through treatment with a solution of hydrogen peroxide in 3 mol % of 5-ethyluminiflavin perchlorate (FIEt+.ClO4) as a catalyst in 55% yield. The reaction of β
Synthesis of tetrafluorinated piperidines from nitrones via a visible-light-promoted annelation reaction
Beilstein J. Org. Chem. 2020, 16, 3104–3108, doi:10.3762/bjoc.16.260
- photocatalyst activated by blue light. The annelation is a result of a radical addition at the nitrone, intramolecular nucleophilic substitution, and reduction of the N–O bond. Keywords: difluoroalkylation; nitrones; organofluorine compounds; photocatalysis; radical addition; Introduction Nitrogen-containing
- fluorinated piperidines based on an accidentally discovered annelation reaction proceeding under reductive conditions. Results and Discussion Nitrone 1a was selected as a model substrate and it was combined with commercially available dibromide 2a under blue light irradiation in the presence of an iridium
- iodine by treatment with zinc, followed by the reaction with iodine monochloride. The iodide 2b reacted quite rapidly with the nitrone but the expected fluoroalkylation product was not observed. Instead, the tetrafluorinated piperidine 3a was obtained in a moderate yield (Table 1, entry 2). Apparently
Recent developments in enantioselective photocatalysis
Beilstein J. Org. Chem. 2020, 16, 2363–2441, doi:10.3762/bjoc.16.197
- •−, which adds to the nitrone via a proposed 6-membered transition state to afford radical cation 286•+. Subsequent hydrogen atom abstraction from TEEDA•+ generates complex 286−. Protonation and displacement by other substrate molecules releases the desired 1,2-amino alcohol products 287 in excellent yields
Oxime radicals: generation, properties and application in organic synthesis
Beilstein J. Org. Chem. 2020, 16, 1234–1276, doi:10.3762/bjoc.16.107
- rule, a C–O bond is formed in intermolecular reactions, intramolecular cyclization generally occurs with the formation of a five-membered cycle of isoxazoline (C–O bond formation) or nitrone (C–N bond formation). Application of the oxime radicals in organic synthesis: intermolecular reactions Selective
- with the formation of alkyl radical 94. The latter attacked the nitrone moiety to form the bicyclic nitroxyl radical 95. When oxime 96 was oxidized with lead(IV) acetate, products 98 and 99 were observed. This result can be explained by the intramolecular attack of iminoxyl radical 97 on the phenyl π
- -unsaturated aliphatic and aryl oximes with TEMPO yielded cyclic nitrones (products 145a–j). The majority of the synthesized cyclic nitrones were disubstituted in α-position to the C=NO group (145a–f,h–j), the unsubstituted nitrone 145g was synthesized in the lowest yield. In the case of 145j–145j’ the
Synthesis of 1-azaspiro[4.4]nonan-1-oxyls via intramolecular 1,3-dipolar cycloaddition
Beilstein J. Org. Chem. 2019, 15, 2036–2042, doi:10.3762/bjoc.15.200
- synthesis of new pyrrolidine nitroxides from 5,5-dialkyl-1-pyrroline N-oxides via the introduction of a pent-4-enyl group to the nitrone carbon followed by an intramolecular 1,3-dipolar cycloaddition reaction and isoxazolidine ring opening. The kinetics of reduction of the new nitroxides with ascorbate were
- -enylmagnesium bromide to the corresponding nitrone, oxidation to alkenylnitrone, intramolecular 1,3-dipolar cycloaddition, and isoxazolidine ring opening. Nitroxide 1 showed both an unexpectedly low reduction rate [6] and long relaxation times t1 and tm at room temperature [4]. Unexpectedly high resistance of
- was carried out in the presence of 2,2,6,6-tetramethylpiperidine-1-oxyl. It should be noted that heating of alkenyl nitrones 7a and 7b gives the corresponding cycloadducts with yields close to quantitative, whereas for nitrone 7c, the complete conversion could not be achieved either at 145 °C or at a
Synthesis and selected transformations of 2-unsubstituted 1-(adamantyloxy)imidazole 3-oxides: straightforward access to non-symmetric 1,3-dialkoxyimidazolium salts
Beilstein J. Org. Chem. 2019, 15, 497–505, doi:10.3762/bjoc.15.43
- interest as so-called ‘nitrone like’ reagents for the synthesis of more complex, imidazole containing systems (Scheme 1) [6]. These imidazole N-oxides are easily accessible via heterocyclization reactions comprising condensation of α-hydroxyiminoketones 2 with formaldimines 3. The latter are known to exist
Synthesis of nonracemic hydroxyglutamic acids
Beilstein J. Org. Chem. 2019, 15, 236–255, doi:10.3762/bjoc.15.22
- with 69 and (2S,4S)-3 [78]. Two other stereoisomers were synthesized in a similar way from (R)-67. By a nitrone–acrylate cycloaddition The isoxazolidine ring can be considered as another cyclic precursor to 4-hydroxyglutamic acids due to the easy cleavage of the N–O bond and high trans
- diastereoselectivities of 1,3-dipolar cycloadditions which allow to control stereochemistries at C3 and C5 [79][80]. To illustrate this concept the E/Z mixture of nitrone 70 was reacted with acrylamide 71 prepared from (2S)-bornane-10,2-sultam to afford mainly (20:1) the isoxazolidine (3S,5S)-72 easily separable from
Oxidative cycloaddition of hydroxamic acids with dienes or guaiacols mediated by iodine(III) reagents
Beilstein J. Org. Chem. 2018, 14, 531–536, doi:10.3762/bjoc.14.39
- adducts 3aa in 96 and 90% yields, respectively (Table 1, entries 10 and 11), BTI showed better results (Table 1, entries 8 and 9). On the other hand, the use of IBA-OTf, which was effective in the oxidative cycloaddition reaction of oximes [20][21], gave nitrone-trifluoromethanesulfonic acid (TfOH
- test this hypothesis, the oxazine 3aa was treated with TfOH in DCM at 40 °C for 18 h and afforded 4 quantitatively. Furthermore, the TfOH-mediated formation of nitrone from such HDA adducts has been reported [23]. It should be mentioned that the structures of 3aa and 4 were determined by single crystal
Conjugated nitrosoalkenes as Michael acceptors in carbon–carbon bond forming reactions: a review and perspective
Beilstein J. Org. Chem. 2017, 13, 2214–2234, doi:10.3762/bjoc.13.220
- afforded azafulvene derivatives 91 (Scheme 34) [82]. Remarkably, the formation of five-membered cyclic nitrone through N-attack of the oxime on the cyano group is more preferable over the six-membered N–O heterocycle. C-Nucleophiles possessing leaving groups have been also used in the construction of N–O
Synthesis of spiro[isoindole-1,5’-isoxazolidin]-3(2H)-ones as potential inhibitors of the MDM2-p53 interaction
Beilstein J. Org. Chem. 2016, 12, 2793–2807, doi:10.3762/bjoc.12.278
- -ethynylbenzamides 1. The latter are easily accessible through ethynylation of N-substituted 2-iodobenzamides, with secondary amines (Scheme 1). Compounds 2a–e, as E/Z mixtures, have been reacted with nitrone 4. Different experimental conditions have been exploited: by reacting the nitrone and dipolarophile in
- toluene solution under reflux, the formation of products was not observed, even after extension of the reaction time to 72 h. Under these conditions the process led only to decomposition of the nitrone with the recovery of unaltered isoindolinone. The best results have been obtained by performing the 1,3
- failed, leading to the degradation of the nitrone and the isolation of the unaltered dipolarophile, so clearly indicating that the steric factors play a crucial role in the cycloaddition process (see computational data). Theoretical calculations The obtained results and stereochemical outcome of the 1,3
Multicomponent reactions: A simple and efficient route to heterocyclic phosphonates
Beilstein J. Org. Chem. 2016, 12, 1269–1301, doi:10.3762/bjoc.12.121
- process involves the 1,3-dipolar cycloaddition of alkynes 182 with in situ generated nitrone 185 to afford isoxazolines 186 which rapidly rearrange to aziridinylphosphonates 183. An efficient method for the synthesis of 1,2,3-triazoles is the copper(I)-catalyzed Husigen cycloaddition of azides with
Copper-mediated synthesis of N-alkenyl-α,β-unsaturated nitrones and their conversion to tri- and tetrasubstituted pyridines
Beilstein J. Org. Chem. 2015, 11, 2097–2104, doi:10.3762/bjoc.11.226
- . Keywords: Chan–Lam; copper; nitrone; oxygen transfer; pyridine; Introduction While most applications of the Chan–Lam reaction are focused on the synthesis of aryl ethers and aryl amines, our group has been interested in the use of the Chan–Lam reaction for the synthesis of O-alkenyl oximes and
- using reaction conditions that we had previously identified as optimal for analogous N-alkenylnitrone syntheses from fluorenone oxime [7]. Nitrone 8aa was successfully isolated in 40% yield using 2 equiv of Cu(OAc)2 and the reaction conditions indicated in Table 1, entry 1. Only the E-nitrone isomer was
- , the scope of the nitrone synthesis was explored by varying the oxime and alkenylboronic acid reagents. As shown in Table 2, chalcone oximes with both electron-rich and electron-poor aryl substituents, as well as heteroaryl substituents, were tolerated for the transformation with electron-donating
Novel stereocontrolled syntheses of tashiromine and epitashiromine
Beilstein J. Org. Chem. 2015, 11, 596–603, doi:10.3762/bjoc.11.66
- intramolecular cyclization of a chiral alkenylated pyrrolidinone, followed by hydroxylation [32], or by the intramolecular ring closure of chiral pyrrolidine diesters followed by ester and oxo group reduction [33], while the syntheses of (+)-epitashiromine starts from a chiral morpholine derivative, with nitrone
Synthesis of rigid p-terphenyl-linked carbohydrate mimetics
Beilstein J. Org. Chem. 2014, 10, 1749–1758, doi:10.3762/bjoc.10.182
- . Unnatural divalent rigid p-terphenyl-linked C-aryl glycosides with 2.0 nm dimension are available using Suzuki cross-couplings. The key compound, a p-bromophenyl-substituted 1,2-oxazine, was prepared by a stereoselective [3 + 3]-cyclization of a D-isoascorbic acid-derived (Z)-nitrone and lithiated TMSE
- ]-cyclization of D-isoascorbic acid-derived (Z)-nitrone 6 and lithiated TMSE-allene 5. Results and Discussion For our synthesis of new divalent carbohydrate mimetics we required 1,2-oxazine derivatives derived from (Z)-nitrone 6 and lithiated alkoxyallenes. The 4-bromophenyl group should allow transition metal
- -promoted coupling reactions to a variety of new compounds. For this purpose the D-erythrose-configured ester 7, easily available from D-isoascorbic acid [28], was converted into nitrone 6 in a three step procedure (Scheme 2). Its reduction with lithium aluminum hydride was performed under standard
N-Alkylated dinitrones from isosorbide as cross-linkers for unsaturated bio-based polyesters
Beilstein J. Org. Chem. 2014, 10, 902–909, doi:10.3762/bjoc.10.88
- -configuration of 3a/b is evident from the signal at 7.90 ppm. With the formation of the nitrone with an E-configuration the proton of the nitron group is exposed to a strong deshielding effect of the N-oxide group, which causes a movement of the signal to higher ppm values [11]. The appearance of the Z-isomer
Synthesis of new enantiopure poly(hydroxy)aminooxepanes as building blocks for multivalent carbohydrate mimetics
Beilstein J. Org. Chem. 2014, 10, 213–223, doi:10.3762/bjoc.10.17
- )-nitrones 3, 6 and 8 were synthesized essentially following known pathways [35] (Scheme 2 and Scheme 3). The new D-erythrose-derived nitrone 3 containing a p-bromophenyl moiety in the dioxolane ring was obtained in a straightforward manner (Scheme 2). Commercially available D-isoascorbic acid (1) was
- ]. Protection with a TBS-group proceeded quantitatively to gain 2 in very good overall efficacy. Final transformation into the desired nitrone 3 was achieved in 83% yield (over two steps) by reduction of the ester using DIBAL-H at low temperature, followed by condensation with N-benzylhydroxylamine according to
- a Dondoni protocol [29]. This route allows the synthesis of enantiopure nitrone 3 in multi-gram scale. The enantiopure (Z)-configured nitrones 6, 8 and 3 were treated with in situ lithiated TMSE-allene at −78 °C furnishing the expected 1,2-oxazines syn-7 [37], syn-9 and syn-10 in high yields and
Gold(I)-catalyzed enantioselective cycloaddition reactions
Beilstein J. Org. Chem. 2013, 9, 2250–2264, doi:10.3762/bjoc.9.264
- the species that participates in the cycloaddition to the nitrone, probably in a concerted pathway, and thus providing the corresponding products with high levels of stereoselectivity [82][83]. Previously, in 2009, J. Zhang had reported a gold(I)-catalyzed 1,3-dipolar [3 + 3] cycloaddition between 2
- . This key intermediate is then trapped by the nitrone to afford XIV, which eventually evolves to the product by an intramolecular cyclization (Scheme 17). Finally, the same group recently reported a related reaction of 1-(1-alkynyl)cyclopropyl ketones such as 28, by means of a gold(I)-catalyzed
- asymmetric [4 + 3] cycloaddition. In this article, the authors demonstrated that a chiral gold catalyst generated from MeO-DTBM-Biphep was able to promote the [4 + 3] cycloaddition between ketone 28 and the nitrone 29, to afford the corresponding 5,7-fused bicyclic furo[3,4-d][1,2]oxazepine 30 in good yield
The chemistry of amine radical cations produced by visible light photoredox catalysis
Beilstein J. Org. Chem. 2013, 9, 1977–2001, doi:10.3762/bjoc.9.234
- oxidized to nitrone 64. Finally, an intramolecular 1,3-dipolar cycloaddition of 64 furnishes isoxazolidine 55. Tetrahydroisoquinolines are arguably the most exploited amines in visible light photoredox catalysis. However, efforts towards expanding the scope of amines have been recently reported. Li [82
Gold-catalyzed cyclization of allenyl acetal derivatives
Beilstein J. Org. Chem. 2013, 9, 1751–1756, doi:10.3762/bjoc.9.202
- ]. We postulate that compounds 2 arise from the attack of 1,3-diones at initially generated allyl cation intermediates I. In the case of electrophilic nitrones, allyl cations I release a proton to form reactive 1-methoxyfulvenes II to achieve a [3 + 2]-nitrone cycloaddition. The versatility of cationic
- alternative route involving the protonation of the fulvene intermediate D because this route would water as a proton source. The formation of the fulvene intermediate D from allyl cation B is assisted by a weak base like nitrone [18]. We envisage that a 1,2-hydrogen shift for the allyl cation B fails to
Some aspects of radical chemistry in the assembly of complex molecular architectures
Beilstein J. Org. Chem. 2013, 9, 557–576, doi:10.3762/bjoc.9.61
- hydroxylamine and hydrazine substituents in order to construct unusual heterocycles [33][34]. One typical illustration is presented in Scheme 14, where unmasking of the hydroxylamine in adduct 70 gives rise to cyclic nitrone 71, which can then be intercepted by a dipolarophile placed in the medium, as shown by
- synthesis of (±)-matrine (43). Synthesis of complex tetralones. Synthesis of functionalised azaindoline and indole derivatives. Synthesis of thiochromanones. Synthesis of complex benzothiepinones. Conditions: 1) CF3COOH; 2) RCHO / AcOH (PMB = p-methoxybenzyl). Formation and capture of a cyclic nitrone
Carbohydrate-auxiliary assisted preparation of enantiopure 1,2-oxazine derivatives and aminopolyols
Beilstein J. Org. Chem. 2012, 8, 662–674, doi:10.3762/bjoc.8.74
- hydroxylated 2H-1,2-oxazine derivatives is presented utilizing the [3 + 3] cyclisation of lithiated alkoxyallenes and an L-erythrose-derived N-glycosyl nitrone as precursors. This key step proceeded only with moderate diastereoselectivity, but allowed entry into both enantiomeric series of the resulting 3,6
- ][12]. Although the reactions of lithiated alkoxyallenes, with nitrones bearing substituents with stereogenic centres at the carbon atom, were studied in our group in great detail [13], N-glycosyl-substituted nitrones have so far not been used as electrophiles for this purpose. This type of nitrone has
- reagents [33]. Here we report on the application of a nitrone with an L-erythronolactone-derived auxiliary for the synthesis of 3,6-dihydro-2H-1,2-oxazine derivatives of type D. Their selected transformations, including hydroboration of the enol ether moiety, oxidative work-up, glycosyl cleavage, and
Synthesis and biological evaluation of nojirimycin- and pyrrolidine-based trehalase inhibitors
Beilstein J. Org. Chem. 2012, 8, 514–521, doi:10.3762/bjoc.8.58
- , deprotection of intermediate 28 afforded monosubstituted urea 16 in only 58% purity. In addition, pyrrolidines 20 and 21 were synthesized in a few steps from nitrone 30 [23]. Catalytic hydrogenation over Pd/C followed by reductive amination in the presence of octanal and NaBH3CN afforded compound 20 in 33
- % yield over two steps (Scheme 3). Grignard addition of octylmagnesium bromide to nitrone 30 proceeded cleanly and gave stereoselectively the “all trans” hydroxypyrrolidine 31 as a single adduct in 84% yield, with a stereoselectivity that was in accordance with previously reported Grignard additions on
- the same nitrone [24]. Final catalytic hydrogenation over Pd/C gave pyrrolidine 21, which was recently synthesized by an enantioselective strategy [25], in 73% yield. Enzyme assays Synthesized compounds 10, 12–14, 16, 17 and 19–21 were tested for their inhibitory activity against insect (C. riparius
Recent developments in gold-catalyzed cycloaddition reactions
Beilstein J. Org. Chem. 2011, 7, 1075–1094, doi:10.3762/bjoc.7.124
- activation of the alkyne group of 10 by the carbophilic gold catalyst (Ph3PAuCl/AgOTf), followed by an intramolecular cyclization that generates the furanyl–gold complex IX. This intermediate is then trapped by the nucleophilic oxygen atom of the nitrone to afford X, which eventually evolves to the final
- [L1(AuCl)2] or (R)-MeO-dtbm-biphep [L2(AuCl)2], with the former being slightly more efficient in certain cases (Scheme 6) [48]. If instead of a nitrone, a nucleophilic α,β-unsaturated imine is used as the second cycloaddition component, furo[3,4-c]azepines such as 12 can be obtained [49]. An example
- nitrone, delivers intermediate XIII, which evolves to the final cycloadduct by ring closure through a favored chair-like conformation. An attack of the nitrone on intermediate XII, to directly generate species XIII, has also been proposed as an alternative pathway. Common to all these reported
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