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Search for "enolate" in Full Text gives 271 result(s) in Beilstein Journal of Organic Chemistry. Showing first 200.
Diastereoselective synthesis of highly substituted cyclohexanones and tetrahydrochromene-4-ones via conjugate addition of curcumins to arylidenemalonates
Beilstein J. Org. Chem. 2024, 20, 2016–2023, doi:10.3762/bjoc.20.177
- double Michael adduct 3n in 56% yield (Table 2, entry 14). A plausible mechanism for the cascade double and triple Michael reactions is shown in Scheme 2. At first, the enolate I of curcumin 1 adds to arylidenemalonate 2 in a Michael fashion resulting enolate II. The ester enolate II might remain in
- equilibrium with 1,3-dicarbonyl enolate I, but the former would be trapped via cyclization involving a diastereoselective 6-endo-trig intramolecular Michael addition to the enone moiety leading to highly substituted cyclohexanone 3. The formation of triple Michael adduct 4 can be attributed to the enolate 3
- curcumins 1 with arylidenemalonate 2 can be explained in terms of the relative stereochemistry of the substituents in the enolate arising from the first Michael addition (Figure 3). Comparison of the two possible transition states TSI and TSII for second Michael addition suggests that a severe 1,3-allylic
Regioselective alkylation of a versatile indazole: Electrophile scope and mechanistic insights from density functional theory calculations
Beilstein J. Org. Chem. 2024, 20, 1940–1954, doi:10.3762/bjoc.20.170
- , presumably due to entropic penalties. Three of four computed resonance forms were all found to be of approximately equal energy. Only the E-enolate form 6 (-N1H-E) was slightly higher in energy by 0.06 kcal/mol likely due to electrostatic destabilization of the oxyanion with N2, however, this difference is
- molecules. Tautomerism of indazole. DFT-calculated deprotonation of 6 with Cs2CO3 in implicit THF with the temperature of the calculation set to 90 °C to simulate the dioxane conditions (top) and energy differences of four enolate resonance structures of 6 calculated as discrete structures. The hybrid is
- identified as 6(N-H) (bottom). DFT-calculated Cs+-coordinated complexes with different enolate forms of 6(N-H) calculated as isolated compounds (top) and calculated intermediates of the reactions of 6(-N1H-Z) and 6(-N1H-E) with Cs+ (bottom). DFT-calculated reaction coordinate diagram for the reaction of 6
Harnessing unprotected deactivated amines and arylglyoxals in the Ugi reaction for the synthesis of fused complex nitrogen heterocycles
Beilstein J. Org. Chem. 2024, 20, 1758–1766, doi:10.3762/bjoc.20.154
- reactions seem to take place through conjugated additions on the enol tautomer of the Ugi adduct. Indeed, the enolate intermediate would explain the stereochemical results, controlled by the configuration in the hemiaminal intermediate and not by the chiral information on the amine, unlike in the case of
Tetrabutylammonium iodide-catalyzed oxidative α-azidation of β-ketocarbonyl compounds using sodium azide
Beilstein J. Org. Chem. 2024, 20, 1510–1517, doi:10.3762/bjoc.20.135
- the starting materials (nucleophilic approach), or rely on more advanced N3-transfer agents (electrophilic approach), over the course of the last years also α-azidations of enolate-type precursors using nucleophilic azide sources under oxidative conditions have been introduced very successfully [24
Towards an asymmetric β-selective addition of azlactones to allenoates
Beilstein J. Org. Chem. 2024, 20, 1504–1509, doi:10.3762/bjoc.20.134
- allenoates 3 delivering highly functionalized α,α-disubstituted α-amino acid derivatives 5 has so far not been systematically addressed (for recent other β-selective additions of enolate precursors to allenoates please see references [31][32][33][34]). Thus, we now became interested in testing this
(Bio)isosteres of ortho- and meta-substituted benzenes
Beilstein J. Org. Chem. 2024, 20, 859–890, doi:10.3762/bjoc.20.78
- ]propellane (129). Gassman reported the initial synthesis of [3.1.1]propellane (129) in 1980 [61], and this was recently optimised by Uchiyama (Scheme 13A) [47]. Cyclisation to the bridged structure 126 was achieved by enolate formation and intramolecular nucleophilic substitution of iodide diester 125. A
Synthesis of 2,2-difluoro-1,3-diketone and 2,2-difluoro-1,3-ketoester derivatives using fluorine gas
Beilstein J. Org. Chem. 2024, 20, 460–469, doi:10.3762/bjoc.20.41
- reactive enolate 1a-enolate. Nitrogen-centered bases react with fluorine gas to form N-fluoroammonium fluorides and fluoride ion [49]. Thus, on addition of tertiary amines, fluorine can react to generate basic fluoride ions and deliver reactive, electrophilic N–F species. Given that Selectfluor is
- anionic 1a–i-enolate species in parallel with N-fluoroammonium ion 6. Fluoride ions formed through the reactions between fluorine and quinuclidine or fluorine and enolate species, may deprotonate 1a–i-enol, to form enolates of 1a–i that are reactive towards both fluorine and N-fluoroammonium ion 6. The
- effective base to facilitate the formation of 1a-enolate from 1a-enol and thus facilitate the initial monofluorination step by either fluorine or N-fluoroammonium ion 6. Carbonate ions are also expected to be highly basic in MeCN, however, their limited solubility is likely to inhibit their ability to act
Mechanisms for radical reactions initiating from N-hydroxyphthalimide esters
Beilstein J. Org. Chem. 2024, 20, 346–378, doi:10.3762/bjoc.20.35
- (Scheme 30B). Then, cesium carbonate deprotonates the enol OH in 145, to provide the enolate form of Breslow’s intermediate 146, which is a suitable reducing agent to trigger the fragmentation of NHPI ester 58 (E°ox = −0.97 V vs SCE in MeCN). Hence, it is proposed that enolate 146 induces the single
Catalytic multi-step domino and one-pot reactions
Beilstein J. Org. Chem. 2024, 20, 254–256, doi:10.3762/bjoc.20.25
- facile stereoselective tandem reaction based on the asymmetric conjugate addition of dialkylzinc reagents to unsaturated acylimidazoles, followed by trapping of the intermediate zinc enolate with carbocations [12]. A practical one-pot synthesis of fluorescent pyrazolo[3,4-b]pyridin-6-ones by reacting 5
Using the phospha-Michael reaction for making phosphonium phenolate zwitterions
Beilstein J. Org. Chem. 2024, 20, 41–51, doi:10.3762/bjoc.20.6
- regarded as stable phosphonium enolate zwitterions. The first zwitterions of this type were published in 1955 [31], but the first crystal structure of a phosphonium enolate zwitterion was reported only in 2007 by Zhu et al., who synthesized the compound via a three-component coupling between an
- between the anionic phenolate and the cationic phosphonium center [32]. Other stable phosphonium enolate or phenolate zwitterions feature P–O distances in the range of 2.60–2.95 Å [28][32]. For comparison, in 1,2-oxaphosphetanes, the covalent bond between P–O is characterized by a distinctly shorter
Anion–π catalysis on carbon allotropes
Beilstein J. Org. Chem. 2023, 19, 1881–1894, doi:10.3762/bjoc.19.140
- introduced in 2017, followed by carbon nanotubes in 2019. Consistent with expectations from theory, anion–π catalysis on carbon allotropes generally increases with polarizability. Realized examples reach from enolate addition chemistry to asymmetric Diels–Alder reactions and autocatalytic ether cyclizations
- catalysis; electromicrofluidics; enolate addition; ether cyclizations; fullerenes; Introduction Anion–π catalysis was introduced ten years ago [1]. The idea is to stabilize anionic transition states on electron-deficient, π-acidic aromatic surfaces (Figure 1A). The true beginning is arguably in 2015
- because it took some time to find the benchmark reaction needed to develop the catalysts (Figure 2) [2]. With this operational enolate chemistry in hand, it quickly became clear that increasing π acidity at the same time decreases the stability of the catalyst [3][4][5]. This suggested that induced rather
Synthesis and biological evaluation of Argemone mexicana-inspired antimicrobials
Beilstein J. Org. Chem. 2023, 19, 1511–1524, doi:10.3762/bjoc.19.108
- considered ways to further enhance this activity. We first explored the effects of structural modifications to berberine itself. The cationic iminium within berberine and its derivatives is susceptible to nucleophilic attack [10][14]. Through use of an acetone enolate, as well as partial or full reduction by
α-(Aminomethyl)acrylates as acceptors in radical–polar crossover 1,4-additions of dialkylzincs: insights into enolate formation and trapping
Beilstein J. Org. Chem. 2023, 19, 1443–1451, doi:10.3762/bjoc.19.103
- atom to zinc enables this SH2 process which represents a rare example of alkylzinc-group transfer to a tertiary α-carbonyl radical. The zinc enolate thus formed readily undergoes β-fragmentation unless it is trapped by electrophiles in situ. Enolates of substrates having free N–H bonds undergo
- enolate with electrophiles in protocols wherein all the reactive partners can be introduced from the start, given that dialkylzinc reagents offer a large functional group tolerance; and 3) the radical character of the process allows for the use of alkyl iodides as alkyl source in multicomponent reactions
- enolate and a new R• that propagates the radical chain (Scheme 1). Initiation occurs upon oxidation of the dialkylzinc reagent by oxygen. The feasibility of such 1,4-addition reactions is fully reliant on the ease of the intermediate enoxyl radical to undergo alkylzinc-group transfer. Secondary α-carbonyl
Photoredox catalysis harvesting multiple photon or electrochemical energies
Beilstein J. Org. Chem. 2023, 19, 1055–1145, doi:10.3762/bjoc.19.81
First synthesis of acylated nitrocyclopropanes
Beilstein J. Org. Chem. 2023, 19, 892–900, doi:10.3762/bjoc.19.67
- proceeded, to produce furan 13 with a 46% yield (Scheme 6). The coordination of two carbonyl groups to the tin species facilitated the ring opening of the cyclopropane ring to afford betaine [7], then the oxygen atom of the enolate attacked the benzyl cation to construct a five-membered ring. The subsequent
Asymmetric tandem conjugate addition and reaction with carbocations on acylimidazole Michael acceptors
Beilstein J. Org. Chem. 2023, 19, 881–888, doi:10.3762/bjoc.19.65
- 10.3762/bjoc.19.65 Abstract We present here a stereoselective tandem reaction based on the asymmetric conjugate addition of dialkylzinc reagents to unsaturated acylimidazoles followed by trapping of the intermediate zinc enolate with carbocations. The use of a chiral NHC ligand provides chiral zinc
- obtained by other conjugate addition reactions. Keywords: acylimidazole; asymmetric catalysis; carbocation; conjugate addition; enolate; Introduction Asymmetric metal-catalyzed conjugate additions provide access to numerous chiral scaffolds. This type of C–C bond formation efficiently enables the
- excellent in asymmetric conjugate additions of dialkylzincs to acylimidazoles [25]. The initial reaction conditions were inspired by literature precedence on conjugate additions. As the first electrophile for trapping of the chiral enolate, we have used tropylium bistriflimide (Scheme 2). Following our
Synthesis of medium and large phostams, phostones, and phostines
Beilstein J. Org. Chem. 2023, 19, 687–699, doi:10.3762/bjoc.19.50
- '-carboxylates 83 in 5–10% yield as byproducts. The major products 84 were generated via Michael addition and the nucleophilic addition–elimination of the carbanion of the generated enolate moiety, while the oxyanion of the enolate moiety attacked the phosphorus to form the byproducts 83 (Scheme 18) [40][41
Enolates ambushed – asymmetric tandem conjugate addition and subsequent enolate trapping with conventional and less traditional electrophiles
Beilstein J. Org. Chem. 2023, 19, 593–634, doi:10.3762/bjoc.19.44
- years of development. The effort of our group to broaden possibilities to engage metal enolates in reactions with new electrophiles is described. The material is divided according to the organometallic reagent employed in the conjugate addition step, and thus to the particular metal enolate formed
- . Short information on applications in total synthesis is also given. Keywords: asymmetric catalysis; conjugate addition; electrophile; enolate; tandem reaction; Introduction The formation of complex chiral molecules is a crucial task of organic synthesis that enables the synthesis of pharmaceuticals
- stereogenic information, thus leading to chiral products. Enolate species are uniquely positioned for reactivity with a broad array of electrophiles and thus allowing quick and efficient construction of highly complex structures from readily available starting materials. Various polar organometallic reagents
Asymmetric synthesis of a stereopentade fragment toward latrunculins
Beilstein J. Org. Chem. 2023, 19, 428–433, doi:10.3762/bjoc.19.32
- oxidation in presence of DMP. The assembly of aldehyde 8 and methyl ketone 15 was envisaged through a stereoselective aldol reaction. After unsuccessful attempts of Mukaiyama aldol reactions with silyl enol ethers [28], we found that dicyclohexylboron enolate 20, made in situ from ketone 15 and Cy2BCl in
Group 13 exchange and transborylation in catalysis
Beilstein J. Org. Chem. 2023, 19, 325–348, doi:10.3762/bjoc.19.28
- -hydroboration of the enone 29 with H-B-9-BBN to give an O-B-9-BBN enolate 30. Electrophilic cyanation of the enolate 30 with NCTS 31, and elimination gave the β-ketonitrile 33 and TsN(Ph)-9-B-BBN 34, which underwent B‒N/B‒H transborylation with HBpin to regenerate the catalyst and give TsN(Ph)-Bpin 35 (Scheme 8
- fluoride 50 to give the ester 51 and FBpin (Scheme 11). The H-B-9-BBN-catalysed 1,4-hydroboration of enones with HBpin was shown by Thomas, including the subsequent functionalisation of the intermediate Bpin-enolate 52 (Scheme 12) [76]. The proposed mechanism began by 1,4-hydroboration of the enone 29 with
- H-B-9-BBN, followed by B‒O/B‒H transborylation with HBpin to give the Bpin-enolate 52 and regenerate H-B-9-BBN (Scheme 12). Isotopic labelling with DBpin and H10Bpin supported this proposal. Fontaine reported that boric acid could be used as a precatalyst for the BH3-catalysed hydroboration of
Strategies to access the [5-8] bicyclic core encountered in the sesquiterpene, diterpene and sesterterpene series
Beilstein J. Org. Chem. 2023, 19, 245–281, doi:10.3762/bjoc.19.23
- )-SmIII enolate 147. The cyclooctane ring was then accessed through the (Z)-SmIII enolate aldol cyclization. The different organosamarium species generated during the cascade cyclization mechanism were hypothesized to drive the diastereoselectivity on each of the stereocenters created during the process
An accelerated Rauhut–Currier dimerization enabled the synthesis of (±)-incarvilleatone and anticancer studies
Beilstein J. Org. Chem. 2023, 19, 204–211, doi:10.3762/bjoc.19.19
- accelerate the reaction. In conventional intermolecular RC reactions, the reaction proceeds by the intermolecular addition of a nucleophilic catalyst to the enone substrate to generate an enolate in the first step. In the second step the enolate ion attacks the other Michael acceptor at β-position in an
- outlined in Scheme 4. We proposed that (±)-rengyolone (3) undergoes a hydroxy-directed intermolecular conjugate addition [11][12][13][14][15] with another equivalent of (±)-rengyolone (3) (enone system) to highly selectively afford intermediate A. Via a rapid intramolecular Michael addition of enolate
- intermediate A tetrahydrofuran intermediate B with cis-fused ring systems is formed as seen in the existing literature [7]. A proton transfer of enolate moiety B yields another enolate C followed by the β-alkoxy elimination [17] of intermediate C to form intermediate D. The intermediate D on protonation leads
Synthetic study toward tridachiapyrone B
Beilstein J. Org. Chem. 2022, 18, 1741–1748, doi:10.3762/bjoc.18.183
- deprotonation of 2-(α’-methoxy-γ-pyrone)-1,3-dithiane. The resulting vinylogous enolate intermediate was trapped with the electrophile 3, amounting to the one-pot preparation of compound 4, having a masked carbonyl function connecting both key fragments [27][28]. Isolated and characterized by Schmitz [17], the
- lithiocyclopentadiene and the enolate intercepted with an alkylating reagent to build the quaternary carbon of 6b (Scheme 2b). This one-pot procedure was reminiscent of our previous study describing the addition of an allylic carbanion, generated from allylstannane with n-BuLi, to 2 which was followed by the addition
- delocalized enolate intermediate 6a·Li. To that end, the addition of lithiocyclopentadiene to 2 was followed by the attendant quenching with a methylating reagent (MeI, Me2SO4, MeOTf) but a complex mixture of products was consistently obtained. To gather information on the reactivity of 6a·Li, the stabilized
Total synthesis of grayanane natural products
Beilstein J. Org. Chem. 2022, 18, 1707–1719, doi:10.3762/bjoc.18.181
- proposes different disconnections. Newhouse identified a C1–C10 disconnection for a radical cyclization and a C6–C7 for an organolithium addition, allowing a convergent approach with A ring and C–D rings as key fragments. In this case, the bicyclo[3.2.1]octane is obtained by a Ni-catalyzed enolate/alkenyl
Redox-active molecules as organocatalysts for selective oxidative transformations – an unperceived organocatalysis field
Beilstein J. Org. Chem. 2022, 18, 1672–1695, doi:10.3762/bjoc.18.179
- ][72]. A recent achievement of the enantioselective hydroxylation of α‑aryl-δ-lactams by O2 is shown in Scheme 5 [73] as an example of such organocatalyzed reaction type. Triethyl phosphite is added to reduce a hydroperoxide, which is initially formed by the enolate oxidation with O2. In summary
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