Syntheses of spliceostatins and thailanstatins: a review

• William A. Donaldson

Beilstein J. Org. Chem. 2020, 16, 1991–2006, doi:10.3762/bjoc.16.166

• (−)-51 (Scheme 6) [16]. An Achmatowicz oxidation [29] with tert-butyl hydroperoxide catalyzed by VO(acac)2 afforded the hemiketal 52, and the ionic reduction [22] of 52 gave the enone (−)-53. The enone transposition of 53 was effected by the addition of methyl-Grignard, followed by the oxidation with PCC

• yield and high enantioselectivity (Scheme 7) [15][16]. The Achmatowicz oxidation and ionic reduction generated the enone 58, which is regioisomeric with 53. The 1,4-addition of lithium dimethylcopper gave the desired cis-55 with high a diastereoselectivity (25:1). The cross-metathesis of 55 with 3

Pauson–Khand reaction of fluorinated compounds

• Jorge Escorihuela,
• Daniel M. Sedgwick,
• Alberto Llobat,
• Mercedes Medio-Simón,
• Pablo Barrio and
• Santos Fustero

Beilstein J. Org. Chem. 2020, 16, 1662–1682, doi:10.3762/bjoc.16.138

• , predictable for unsymmetrical alkynes (things are more complex regarding the olefin). Generally, the most sterically encumbered substituent of the alkyne occupies the proximal position in the enone system. This is dictated by the migratory insertion of the olefin into the most accessible Co–C bond (Scheme 3

• ). This trend is strictly followed by terminal alkynes, for which exclusive formation of the α-substituted enone is observed, while mixtures are usually obtained with internal dissymmetric alkynes, although the major product follows the aforementioned trend [41]. On the other hand, for alkynes bearing

• )8 followed by the addition of NMO), and starting from the pure anti diastereoisomer of 1,7-enyne 20, the expected bicyclic enone was obtained in good yield and high diastereoselectivity (de > 95%). An attempt to extend the PKR to the formation of a fused tricyclic structure, starting from 1,7-enyne

An overview on disulfide-catalyzed and -cocatalyzed photoreactions

• Yeersen Patehebieke

Beilstein J. Org. Chem. 2020, 16, 1418–1435, doi:10.3762/bjoc.16.118

• subsequent SET from the radical 60 to the thiyl radical yields the allylic cation 61 and a thiolate anion. The following proton abstraction by this thiolate anion from the intermediate 62 gives the enone 63 and thiophenol to complete the oxidation. In the hydrogenation step, the addition of a thiyl radical

• to the enone 63 and posterior hydrogen transfer from thiol to the intermediate 64 forms the ketone intermediate 65 (pathway 1). This ketone intermediate 65 is also accessible by an ionic addition in the dark (pathway 2). The tautomerization of the ketone 65 yields the enol form 66, which reacts with

Recent synthesis of thietanes

• Jiaxi Xu

Beilstein J. Org. Chem. 2020, 16, 1357–1410, doi:10.3762/bjoc.16.116

Recent applications of porphyrins as photocatalysts in organic synthesis: batch and continuous flow approaches

• Rodrigo Costa e Silva,
• Luely Oliveira da Silva,
• Aloisio de Andrade Bartolomeu,
• Timothy John Brocksom and
• Kleber Thiago de Oliveira

Beilstein J. Org. Chem. 2020, 16, 917–955, doi:10.3762/bjoc.16.83

• steps an electrochemical cyclization and an endoperoxidation photocatalyzed by TPP in an almost gram-scale (Scheme 38) [88]. In 2020, Burchill and George reported a 0.5 g-scale ene-reaction with singlet oxygen and a cromene derivative, thus giving a conjugated enone after a Kornblum–DeLaMare

Combining enyne metathesis with long-established organic transformations: a powerful strategy for the sustainable synthesis of bioactive molecules

• Valerian Dragutan,
• Ileana Dragutan,
• Albert Demonceau and
• Lionel Delaude

Beilstein J. Org. Chem. 2020, 16, 738–755, doi:10.3762/bjoc.16.68

• metathesis (RCM) [67][68]. Starting from 3-cyanocyclohex-2-enone, the authors obtained a versatile intermediate able to provide the appropriate dienyne precursors (A–C, Scheme 4) by multicomponent Grignard addition-alkylations. Through divergent cyclizations involving a chemoselective enyne metathesis

Combination of multicomponent KA² and Pauson–Khand reactions: short synthesis of spirocyclic pyrrolocyclopentenones

• Riccardo Innocenti,
• Elena Lenci,
• Gloria Menchi and
• Andrea Trabocchi

Beilstein J. Org. Chem. 2020, 16, 200–211, doi:10.3762/bjoc.16.23

• cyclopentenone ring [37], as this heterocycle is a powerful synthon for the synthesis of a variety of bioactive target molecules, due to the broad diversity of chemical modifications available for the enone structural motif [38]. The most common approach to access such chemotype is the Pauson–Khand (PK) reaction

• Pauson–Khand conditions (Table 1,entry 14). The synthetic utility of the spiro derivatives resulting from the combined KA2/Pauson–Khand process to generate second-generation molecular scaffolds was tested on compound 5 by applying representative reactions on the enone structural motif (Scheme 3). The

• imposed by the adjacent phenyl and cyclohexyl rings [59]. The treatment of compound 5 under Schmidt reaction conditions with sodium azide in TFA [60] resulted in the conversion to the corresponding six-membered ring lactam 39 in 41% yield, demonstrating the reactivity of the enone 5 at the carbonyl group

Synthetic terpenoids in the world of fragrances: Iso E Super^® is the showcase

• Alexey Stepanyuk and
• Andreas Kirschning

Beilstein J. Org. Chem. 2019, 15, 2590–2602, doi:10.3762/bjoc.15.252

• ]. Oxidation, iodocarboxylation and elimination yielded the lactone 43. A series of functional group manipulations provided enone 44, which underwent a cuprate-mediated Michael addition and liberation of the aldehyde 46 upon ozonolysis. After intramolecular aldol condensation the resulting enone 47 was

Chiral terpene auxiliaries V: Synthesis of new chiral γ-hydroxyphosphine oxides derived from α-pinene

• Anna Kmieciak and
• Marek P. Krzemiński

Beilstein J. Org. Chem. 2019, 15, 2493–2499, doi:10.3762/bjoc.15.242

• sodium carbonate to give (+)-3-methyleneverbanone (5) in 57% yield from 3. α,β-Unsaturated ketone 5 was exclusively reduced to allylic alcohol (1R,2R,4S,5R)-3-methyleneneoisoverbanol (6), using the Luche method [24]. 1,2-Reduction of enone 5 was achieved with sodium borohydride in the presence of cerium

• sulfuric acid under biphasic conditions. (−)-Isopinocamphone (8) was purified by fractional distillation and isolated in 78% yield. Then, 8 was subjected to an analogous reaction sequence that was used for (+)-verbanone (3), i.e., the synthesis of the enone in the first step followed by its 1,2-reduction

Synthesis of acremines A, B and F and studies on the bisacremines

• Nils Winter and
• Dirk Trauner

Beilstein J. Org. Chem. 2019, 15, 2271–2276, doi:10.3762/bjoc.15.219

• later stage the optical purity could be improved (see below). Diol protection gave dioxolane 14, which underwent Saegusa oxidation to afford enone 15. Subsequent α-iodination gave access to α-iodoenone 16, which could be stereoselectively reduced under Corey–Itsuno conditions to yield allylic alcohol 17

Recent advances on the transition-metal-catalyzed synthesis of imidazopyridines: an updated coverage

• Gagandeep Kour Reen,
• Ashok Kumar and
• Pratibha Sharma

Beilstein J. Org. Chem. 2019, 15, 1612–1704, doi:10.3762/bjoc.15.165

• 61 in a one-pot fashion, by reacting 2-AP 3 and 1,3-diphenylprop-2-yn-1-one 60 under the given conditions. This one-pot methodology provided the final product with a yield of 50% (Scheme 21). For pyridine synthesis, both N-pyridyl as well as enone fragment have well tolerated a large number of

Synthesis and biological evaluation of truncated derivatives of abyssomicin C as antibacterial agents

• Leticia Monjas,
• Peter Fodran,
• Johanna Kollback,
• Carlo Cassani,
• Thomas Olsson,
• Maja Genheden,
• D. G. Joakim Larsson and
• Carl-Johan Wallentin

Beilstein J. Org. Chem. 2019, 15, 1468–1474, doi:10.3762/bjoc.15.147

• methicillin- and vancomycin-resistant Staphylococcus aureus (MRSA and VRSA) with minimum inhibitory concentration (MIC) values of 4 and 13 µg/mL, respectively [4]. AbC belongs to a small family of NPs and two congeners of this family lacking the enone functionality, abyssomicins B and D, were discovered at

• the same time, and these compounds did not show any antibacterial activity (Figure 1). Consequently, the enone moiety of AbC was proposed to play an essential role in the antibiotic activity. Indeed, in a subsequent study it was shown that AbC has a unique mechanism of action amongst NPs: it is a

• cysteine residue in the immediate proximity to the active site and the enone moiety of AbC. The PABA pathway is essential in bacteria but absent in humans, making AbC a promising compound for further development towards an antibiotic drug candidate. Because of its intriguing structure and antibacterial

Synthesis of cis-hydrindan-2,4-diones bearing an all-carbon quaternary center by a Danheiser annulation

• Gisela V. Saborit,
• Carlos Cativiela,
• Ana I. Jiménez,
• Josep Bonjoch and
• Ben Bradshaw

Beilstein J. Org. Chem. 2018, 14, 2597–2601, doi:10.3762/bjoc.14.237

• hydrindan-2,4-diones. Stereoview of cis-hydrindane 8. Decahydroquinoline 1 as a versatile building block for Lycopodium alkaloid synthesis. A de novo approach to 3a-substituted cis-hydrindan-2,4-diones. Synthesis of enone 4 and the Danheiser annulation. The depicted compounds are all racemic. Transformation

Microwave-assisted synthesis of biologically relevant steroidal 17-exo-pyrazol-5'-ones from a norpregnene precursor by a side-chain elongation/heterocyclization sequence

• Gergő Mótyán,
• László Mérai,
• Márton Attila Kiss,
• Zsuzsanna Schelz,
• Izabella Sinka,
• István Zupkó and
• Éva Frank

Beilstein J. Org. Chem. 2018, 14, 2589–2596, doi:10.3762/bjoc.14.236

• with its β-ketoester moiety to give 17-exo-heterocycles, but also with its enone part to provide ring D-condensed pyrazolines [27]. Therefore, the ring-closure reactions of 4 with unsubstituted and monosubstituted hydrazines as binucleophilic reagents were investigated next. First, compound 4 was

Studies towards the synthesis of hyperireflexolide A

• G. Hari Mangeswara Rao

Beilstein J. Org. Chem. 2018, 14, 2106–2111, doi:10.3762/bjoc.14.185

• with 2-bromopropene followed by lactonization. Enone 3 could be synthesized from 4 by installation of the methyl group at C-10 followed by cross metathesis reaction. Compound 4 could be obtained from the γ-lactone-fused cyclopentane 5 by deprotection of C-9 followed by allylation at C-8. Previously, we

• performed using Grubbs’ 1st generation catalyst (3–20 mol %) was unsuccessful. Treatment of 10 with ethyl vinyl ketone using Grubbs’ 2nd generation catalyst (3 mol %) in the presence of CH2Cl2 furnished (E)-enone 11 in 77% yield as shown in Scheme 4. In the 1H NMR spectrum, 11 showed a signal at 6.13 ppm as

• doublet with coupling constant 15.8 Hz (trans-configuration) for the α-proton of enone [34][35][36][37]. After successfully synthesizing the side chain via cross-metathesis, our next task was the steresoselective epoxidation of (E)-enone 11. Unfortunately, the stereoselective epoxidation of 11 under basic

Synthesis of spirocyclic scaffolds using hypervalent iodine reagents

• Fateh V. Singh,
• Priyanka B. Kole,
• Saeesh R. Mangaonkar and
• Samata E. Shetgaonkar

Beilstein J. Org. Chem. 2018, 14, 1778–1805, doi:10.3762/bjoc.14.152

• of palmarumycin CP1 were synthesized later which were showing good thioredoxin–thioredoxin reductase (Trx-1/TrxR) inhibitory activity [129]. It was observed that the introduction of enone functionality in naphthoquinone spiroketal enhances the biological activity of palmarumycin 138. Furthermore, Ley

Lanyamycin, a macrolide antibiotic from Sorangium cellulosum, strain Soce 481 (Myxobacteria)

• Lucky S. Mulwa,
• Rolf Jansen,
• Dimas F. Praditya,
• Kathrin I. Mohr,
• Patrick W. Okanya,
• Joachim Wink,
• Eike Steinmann and
• Marc Stadler

Beilstein J. Org. Chem. 2018, 14, 1554–1562, doi:10.3762/bjoc.14.132

• configuration of the substituted Δ17,18 double bond was derived from the ROESY correlations between methyl-41 and methylene protons 16a and 16b and between methine-17 and methylenes H-20a and H-20b. The latter simultaneously indicated the s-trans configuration of the enone and explained the observation of a

Aminosugar-based immunomodulator lipid A: synthetic approaches

• Alla Zamyatina

Beilstein J. Org. Chem. 2018, 14, 25–53, doi:10.3762/bjoc.14.3

CF₃SO₂X (X = Na, Cl) as reagents for trifluoromethylation, trifluoromethylsulfenyl-, -sulfinyl- and -sulfonylation and chlorination. Part 2: Use of CF₃SO₂Cl

• Hélène Chachignon,
• Hélène Guyon and
• Dominique Cahard

Beilstein J. Org. Chem. 2017, 13, 2800–2818, doi:10.3762/bjoc.13.273

• reduction potential of Cu(dap)2Cl in the excited state, and its important ability to mediate the transfer of the Cl atom. Consequently, a variety of electron-deficient alkenes, such as N-arylacrylamides, acrylonitrile, acrylate and enone derivatives furnished their chlorotrifluoromethylated analogues in

Vinylphosphonium and 2-aminovinylphosphonium salts – preparation and applications in organic synthesis

• Anna Kuźnik,
• Roman Mazurkiewicz and
• Beata Fryczkowska

Beilstein J. Org. Chem. 2017, 13, 2710–2738, doi:10.3762/bjoc.13.269

• of triphenylphosphine oxide and the formation of a new C–C bond between the carbon atom at the α-position of the phosphonium salt and the carbon atom of the carbonyl group of the carboxylate anion. The obtained enone 123 was then trapped by reaction with alkyl isocyanide, which finally led to ring

Synthesis, effect of substituents on the regiochemistry and equilibrium studies of tetrazolo[1,5-a]pyrimidine/2-azidopyrimidines

• Elisandra Scapin,
• Paulo R. S. Salbego,
• Caroline R. Bender,
• Alexandre R. Meyer,
• Anderson B. Pagliari,
• Tainára Orlando,
• Geórgia C. Zimmer,
• Clarissa P. Frizzo,
• Helio G. Bonacorso,
• Nilo Zanatta and
• Marcos A. P. Martins

Beilstein J. Org. Chem. 2017, 13, 2396–2407, doi:10.3762/bjoc.13.237

• atom of the enone, both soft sites of the starting materials [29]. In recent research, we developed an efficient method to obtain 1,2,4-triazolo[1,5-a]pyrimidines from the cyclocondensation reaction of 1,1,1-trifluoro-4-metoxy-3-alken-2-one or β-enaminones with 5-amino-1,2,4-triazole. The methodology

An efficient synthesis of a C₁₂-higher sugar aminoalditol

• Łukasz Szyszka,
• Anna Osuch-Kwiatkowska,
• Mykhaylo A. Potopnyk and
• Sławomir Jarosz

Beilstein J. Org. Chem. 2017, 13, 2146–2152, doi:10.3762/bjoc.13.213

• the coupling of two simple monosaccharides and subsequent transformation of the resulting enone into the protected C12-sugar 1. The conversion of the latter into alditol 2 allowed us to prepare derivative 3 having a 18-membered ring (Figure 1) [8]. Higher sugar 1 has a substantial synthetic potential

Preparation of imidazo[1,2-a]-N-heterocyclic derivatives with gem-difluorinated side chains

• Layal Hariss,
• Kamal Bou Hadir,
• Mirvat El-Masri,
• Thierry Roisnel,
• René Grée and
• Ali Hachem

Beilstein J. Org. Chem. 2017, 13, 2115–2121, doi:10.3762/bjoc.13.208

• demonstrate the regiochemistry of the reaction. These cascade reactions proceed first through a Michael addition of the primary amine on the enone, followed by an intramolecular cyclization by the pyridine/pyrimidine nucleus. Unfortunately, no crystal structure could be obtained for the imidazopyrimidines and

• washed with water, dried (Na2SO4) and concentrated in vacuo. The crude product was purified by chromatography on silica gel, using a mixture of petroleum ether/ethyl acetate as eluent. Enone 6a was isolated as a colorless oil (335 mg, 62% yield); Rf 0.43 (petroleum ether/AcOEt 9:1); 1H NMR (CDCl3, 500

• -aminopyridine (20 mg, 0.21 mmol, 1.2 equiv), enone 6a (51 mg, 0.17 mmol, 1 equiv), Cu(OAc)2·H2O (3.6 mg, 0.02 mmol, 10 mol %), and 1,10-phenanthroline (2.5 μL, 0.02 mmol, 10 mol %) in chlorobenzene (1 mL) was stirred in a reaction tube at 160 °C under an O2 atmosphere. After 25 h, 19F NMR monitoring indicated

NHC-catalyzed cleavage of vicinal diketones and triketones followed by insertion of enones and ynones

• Ken Takaki,
• Makoto Hino,
• Akira Ohno,
• Kimihiro Komeyama,
• Hiroto Yoshida and
• Hiroshi Fukuoka

Beilstein J. Org. Chem. 2017, 13, 1816–1822, doi:10.3762/bjoc.13.176

• the 9- and 14-membered 1,4-diketones 7b and 7c at elevated temperature, respectively. Next, we investigated the NHC-catalyzed reaction of 1,2,3-triketone 9 with enone 6a. Since the central carbonyl group of 9 could be more electrophilic than the others at 1- and 3-positions, nucleophilic addition of

• NHC followed by migration of one neighboring acyl group to the central carbonyl oxygen would generate bisacylated Breslow intermediate 10 (Scheme 5). If this species behaves in a similar manner as the monoacylated intermediate C derived from 1,2-diketone 1, its reaction with enone 6a would be expected

• obtained unexpectedly, its reactivity and role in the catalytic cycle were investigated. The stoichiometric reaction of 12 with phenyl vinyl ketone (6a) in the presence of DIPEA gave the product 13 in 94% yield, while no product was formed without the base. Moreover, the reaction of benzil 1d with enone 6a

New electroactive asymmetrical chalcones and therefrom derived 2-amino- / 2-(1H-pyrrol-1-yl)pyrimidines, containing an N-[ω-(4-methoxyphenoxy)alkyl]carbazole fragment: synthesis, optical and electrochemical properties

• Daria G. Selivanova,
• Alexei A. Gorbunov,
• Olga A. Mayorova,
• Alexander N. Vasyanin,
• Igor V. Lunegov,
• Elena V. Shklyaeva and
• Georgii G. Abashev

Beilstein J. Org. Chem. 2017, 13, 1583–1595, doi:10.3762/bjoc.13.158

• structure of side chains [10]. In this paper we describe a synthetic approach to some new D–π–A–D conjugated systems which include 9-[ω-(4-methoxyphenoxy)alkyl]carbazole as a donor fragment (D) and prop-2-enone and pyrimidine units as electron acceptor moieties (A). The optical and electrochemical