Iron-catalyzed domino coupling reactions of π-systems

• Austin Pounder and
• William Tam

Beilstein J. Org. Chem. 2021, 17, 2848–2893, doi:10.3762/bjoc.17.196

• cyclization with the aryl ring constructs the 6-membered heterocyclic framework. In 2015, the Li group investigated the radical addition/cyclization of olefinic malonate and β-diketone compounds 96 with aldehydes 97 (Scheme 19) [97]. The reaction was feasible with ketones; however, lower product yields were

α-Ketol and α-iminol rearrangements in synthetic organic and biosynthetic reactions

• Scott Benz and
• Andrew S. Murkin

Beilstein J. Org. Chem. 2021, 17, 2570–2584, doi:10.3762/bjoc.17.172

• conversion of 3 into the cyclohexanone product 4 (Figure 2) [4]. The best results were obtained with 2-[4-(S)-tert-butyloxazolin-2-yl]pyridine ((S)-5), which gave >90% yield of (S)-4 in 46% ee. In a similar investigation except with copper(II) as the metal and β-hydroxy-α-diketone 6 as the substrate, the

Visible-light-mediated copper photocatalysis for organic syntheses

• Yajing Zhang,
• Qian Wang,
• Zongsheng Yan,
• Donglai Ma and
• Yuguang Zheng

Beilstein J. Org. Chem. 2021, 17, 2520–2542, doi:10.3762/bjoc.17.169

• undergoes radical addition with the N-substituted maleimide (Scheme 25). In 2017, Wu and co-workers [94] reported the α-amino C−H functionalization of aromatic amines 51 with nucleophiles, including arynes or aromatic olefins 52, indoles, acyclic β-ketoester 53, and β-diketone 54 (Scheme 26). Mechanistic

A recent overview on the synthesis of 1,4,5-trisubstituted 1,2,3-triazoles

• Pezhman Shiri,
• Ali Mohammad Amani and
• Thomas Mayer-Gall

Beilstein J. Org. Chem. 2021, 17, 1600–1628, doi:10.3762/bjoc.17.114

• esters 29, such as 1,3-diketones, β-ketoesters, cyclic 1,3-diketone (dimedone), and β-ketoamide, respectively, to afford desired 1,4,5-trisubstituted 1,2,3-triazoles containing glycosyl with high yield. It should be pointed out that no byproducts were recognized under optimized reaction conditions. In

A straightforward conversion of 1,4-quinones into polycyclic pyrazoles via [3 + 2]-cycloaddition with fluorinated nitrile imines

• Greta Utecht-Jarzyńska,
• Karolina Nagła,
• Grzegorz Mlostoń,
• Heinz Heimgartner,
• Marcin Palusiak and
• Marcin Jasiński

Beilstein J. Org. Chem. 2021, 17, 1509–1517, doi:10.3762/bjoc.17.108

• , [3 + 2]-cycloadditions leading to five-membered heterocycles are less often employed in spite of the high dipolarophilicity of the α,β-unsaturated diketone system [6][7][8][9]. Notably, in the already reported reactions of propargylic 1,3-dipoles, such as nitrile oxides or nitrile ylides, with 1,4

Icilio Guareschi and his amazing “1897 reaction”

• Gian Cesare Tron,
• Alberto Minassi,
• Giovanni Sorba,
• Mara Fausone and
• Giovanni Appendino

Beilstein J. Org. Chem. 2021, 17, 1335–1351, doi:10.3762/bjoc.17.93

• reaction reported in 1898 [50]. It involves the reaction of a β-dicarbonyl (ester or diketone) with a primary amine or ammonia and a cyanoacetic ester. The mechanism of this condensation closely resembles the three-component version of the Hantzsch pyridine synthesis and generates 6-hydroxypyridones. Also

Microwave-assisted multicomponent reactions in heterocyclic chemistry and mechanistic aspects

• Shivani Gulati,
• Stephy Elza John and
• Nagula Shankaraiah

Beilstein J. Org. Chem. 2021, 17, 819–865, doi:10.3762/bjoc.17.71

• ; 4, Figure 1) [36][37]. The relevance of acridine in drug discovery galvanized Singh and co-workers [38] to develop a water-promoted three-component reaction involving aldehydes 5, cyclic 1,3-diketone 6 and ammonium acetate powered by microwave irradiation resulting in 4-arylacridinediones 7 in

• -ones 24 using substituted phenylenediamine 23, aldehydes 5 and cyclic 1,3-diketone such as tetronic acid 6c under microwave irradiation in aqueous conditions delivering the product in good yields (70–89%). The use of a non-polar solvent resulted in the formation of side products like benzimidazole

• . The postulated mechanism indicates the formation of acylimine A from the lanthanum oxide-catalyzed reaction of aldehyde and 77. Further, addition of acyclic 1,3-diketone ester enolate to acylamine A form B which upon subsequent cyclization and dehydration resulted in the formation of desired products

Annulation of a 1,3-dithiole ring to a sterically hindered o-quinone core. Novel ditopic redox-active ligands

• Sergey V. Norkov,
• Anton V. Cherkasov,
• Andrey S. Shavyrin,
• Maxim V. Arsenyev,
• Viacheslav A. Kuropatov and
• Vladimir K. Cherkasov

Beilstein J. Org. Chem. 2021, 17, 273–282, doi:10.3762/bjoc.17.26

• -methide moiety, compound 6c should exhibit a more complicated redox behavior compared to parent o-quinone. Despite 1,3-diketones presumably exist as enol tautomers [30], they are also often used as active methylene compounds. The introduction of a 1,3-diketone fragment at the backbone of the o-quinone

All-carbon [3 + 2] cycloaddition in natural product synthesis

• Zhuo Wang and
• Junyang Liu

Beilstein J. Org. Chem. 2020, 16, 3015–3031, doi:10.3762/bjoc.16.251

• intramolecular cycloaddition to give 44. Freshly prepared 44 was converted to diyl 45 followed by another cycloaddition to give the tetraquinane 46. A four-step synthesis from the tetraquinane 46 gave diketone 47. Treatment of sulfoximine 48 with n-butyllithium generated the corresponding anion, which

Synthesis of 1,4-benzothiazinones from acylpyruvic acids or furan-2,3-diones and o-aminothiophenol

• Ekaterina E. Stepanova,
• Maksim V. Dmitriev and
• Andrey N. Maslivets

Beilstein J. Org. Chem. 2020, 16, 2322–2331, doi:10.3762/bjoc.16.193

• similar situation was observed with tert-butylfurandione 5m. Notably, in case of the reaction of phenylfurandione 5a with chloro-substituted o-aminothiophenol 1b, diketone 6 [26] was isolated as the product instead of the expected compound 4n (Scheme 8). Diketone 6 was formed when the SH group of

• . Isolated yields are shown. Plausible scheme of the formation of diketone 6. Reaction of acylpyruvic acid 2a with o-aminothiophenol (1a) in the presence of carbodiimides in various solvents. Reaction of furandione 5a with o-aminothiophenol (1a) in various solvents.a Supporting Information Supporting

Synthetic approaches to bowl-shaped π-conjugated sumanene and its congeners

• Shakeel Alvi and
• Rashid Ali

Beilstein J. Org. Chem. 2020, 16, 2212–2259, doi:10.3762/bjoc.16.186

• on subsequent Tamao–Fleming oxidation provided the exo-diol 18 in an overall good yield with 99% enantiomeric excess (Scheme 3). Furthermore, the diol 18 was converted into the corresponding diketone 19 using pyridinium chlorochromate (PCC) as an oxidizing agent. Interestingly, they have also

• performed the similar transformation in almost identical yield using Swern oxidation reaction conditions. The diketone 19 was then transformed into the enantiopure iodonorbornanone 22 in three steps which on further regioselective Pd-catalyzed cyclotrimerization furnished the syn-benzocyclotrimer 23 in 55

Tuneable access to indole, indolone, and cinnoline derivatives from a common 1,4-diketone Michael acceptor

• Dalel El-Marrouki,
• Sabrina Touchet,
• Abderrahmen Abdelli,
• Hédi M’Rabet,
• Mohamed Lotfi Efrit and
• Philippe C. Gros

Beilstein J. Org. Chem. 2020, 16, 1722–1731, doi:10.3762/bjoc.16.144

• -tetrahydrocinnoline) derivatives in moderate to excellent yields. Keywords: cinnoline; 1,4-diketone; indole; indolone; N-heterocycle; Introduction Nitrogen-containing heterocycles are widespread in plenty of molecules of interest, either in materials science, optics, electronics, or biology [1][2][3][4]. They are

• process, leading respectively to an indole 6 (after dehydration and aromatization) or an indolone 7. The reaction was first investigated by mixing the diketone 5b as the Michael acceptor and benzylamine under various conditions (Table 1). We first investigated the reactivity in the presence of a set of

• reaction time on the reaction outcome, we reduced the time to 3 h also under the classical refluxing conditions from Table 1, entry 11 and obtained a partial conversion of the starting diketone 5b. Despite the side formation of the indolone 7b in Table 1, entry 5, these conditions were applied to several

An overview on disulfide-catalyzed and -cocatalyzed photoreactions

• Yeersen Patehebieke

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

• of visible light, oxygen, and disulfide [15]. The diaryl-1,2-diketone products can serve as an important structural component of many natural products and bioactive molecules. This method works for a broad range of substrates with high yields (77–97%). A plausible mechanism for this reaction is that

• give the four-membered ring intermediate 29. Finally, the rearrangement of the four-membered intermediate provides the diketone 30 as the product (Scheme 8). In 2017, Wang and co-workers reported an oxidative cleavage of aromatic alkenes at ambient temperature with visible-light irradiation, using

Synthesis of new fluorescent molecules having an aggregation-induced emission property derived from 4-fluoroisoxazoles

• Kazuyuki Sato,
• Akira Kawasaki,
• Yukiko Karuo,
• Atsushi Tarui,
• Kentaro Kawai and
• Masaaki Omote

Beilstein J. Org. Chem. 2020, 16, 1411–1417, doi:10.3762/bjoc.16.117

• fluorinated diketone, 2-fluoro-1,3-diphenylpropane-1,3-dione (7a), the corresponding enaminoketone 8a was obtained in only low yield (Scheme 4, entry 4) and we did not attempt the conversion of 8a towards the α-fluorinated boron ketoiminate 9a. Next, we attempted the selective fluorination of 6b to obtain the

• diketone (Scheme 5). As an alternative method to synthesize F-BKIs 9, we turned our attention to the ring-opening reaction of isoxazoles. The reductive cleavage of the N–O bond in isoxazoles can be achieved by transition metals or their complexes to give the corresponding enaminoketones [35][37

One-pot synthesis of substituted pyrrolo[3,4-b]pyridine-4,5-diones based on the reaction of N-(1-(4-hydroxy-6-methyl-2-oxo-2H-pyran-3-yl)-2-oxo-2-arylethyl)acetamide with amines

• Valeriya G. Melekhina,
• Andrey N. Komogortsev,
• Boris V. Lichitsky,
• Vitaly S. Mityanov,
• Artem N. Fakhrutdinov,
• Arkady A. Dudinov,
• Vasily A. Migulin,
• Yulia V. Nelyubina,
• Elizaveta K. Melnikova and
• Michail M. Krayushkin

Beilstein J. Org. Chem. 2019, 15, 2840–2846, doi:10.3762/bjoc.15.277

• possibility includes the attack of an amine, and pyranone ring-opening to afford the acyclic intermediate 8 (Scheme 3A). Then, the latter undergoes cyclization to intermediate diketone 9. The alternative approach includes an initial condensation of amine and aryl ketone to give the enamine intermediate 10

• , which can subsequently undergo opening of the pyranone ring, yielding dihydropyrrolone 9 (Scheme 3B). Following this, the diketone-containing substituent of 9 reacts with a second equivalent of amine, forming the final enaminone 7. After this general synthetic method for enaminone targets had been

Iodine-mediated hydration of alkynes on keto-functionalized scaffolds: mechanistic insight and the regiospecific hydration of internal alkynes

• Zachary Lee,
• Brandon R. Jones,
• Nyochembeng Nkengbeza,
• Michael Phillips,
• Kayla Valentine,
• Alexis Stewart,
• Brandon Sellers,
• Nicholas Shuber and
• Karelle S. Aiken

Beilstein J. Org. Chem. 2019, 15, 2747–2752, doi:10.3762/bjoc.15.265

• -endo-dig cyclization would result in diketone 18. Significantly, the iodine-mediated hydration of all substrates 11 that were studied gave rise to one type of product, 15 (Scheme 3). This indicated that the reaction with alkyl-capped, internal alkynes occurred exclusively through the 5-exo-dig route, a

Fluorescent phosphorus dendrimers excited by two photons: synthesis, two-photon absorption properties and biological uses

• Anne-Marie Caminade,
• Artem Zibarov,
• Eduardo Cueto Diaz,
• Aurélien Hameau,
• Maxime Klausen,
• Kathleen Moineau-Chane Ching,
• Jean-Pierre Majoral,
• Jean-Baptiste Verlhac,
• Olivier Mongin and
• Mireille Blanchard-Desce

Beilstein J. Org. Chem. 2019, 15, 2287–2303, doi:10.3762/bjoc.15.221

• derivatives grafted on the surface of phosphorhydrazone dendrimers. In this case, a β-diketone functionalized by a phenol was first grafted on the surface of the dendrimer [47], then BF3 was added to obtain the dioxaborines (Scheme 3). Monomer, dimer, and all generations of the dendrimer from zero (6 terminal

Superelectrophilic carbocations: preparation and reactions of a substrate with six ionizable groups

• Sean H. Kennedy,
• Makafui Gasonoo and
• Douglas A. Klumpp

Beilstein J. Org. Chem. 2019, 15, 1515–1520, doi:10.3762/bjoc.15.153

• benzaldehyde. A nickel-catalyzed procedure gives the dipyridyl intermediate 7 [13]. This is easily oxidized to the diketone 8 and reaction of this substance with 2-lithiopyridine gives the precursor 9. The diol 9 is a substrate with six ionizable groups. Upon ionization in superacidic CF3SO3H (triflic acid

Multicomponent reactions (MCRs): a useful access to the synthesis of benzo-fused γ-lactams

• Edorta Martínez de Marigorta,
• Jesús M. de Los Santos,
• Ana M. Ochoa de Retana,
• Javier Vicario and
• Francisco Palacios

Beilstein J. Org. Chem. 2019, 15, 1065–1085, doi:10.3762/bjoc.15.104

• start with the formation of an imine intermediate between the aldehyde function of 33 and the amine 2, followed by a nucleophilic attack by the diketone and a final intramolecular cyclization, the Han group proposes a different pathway, with an initial deprotonation of ketoacid 34 (R2 = Me, Ar, R3 = OH

The LANCA three-component reaction to highly substituted β-ketoenamides – versatile intermediates for the synthesis of functionalized pyridine, pyrimidine, oxazole and quinoxaline derivatives

• Tilman Lechel,
• Roopender Kumar,
• Mrinal K. Bera,
• Reinhold Zimmer and
• Hans-Ulrich Reissig

Beilstein J. Org. Chem. 2019, 15, 655–678, doi:10.3762/bjoc.15.61

• OX17. This sequence demonstrates the potential of the C-5 functionalized oxazoles to be used for further transformations (see below). The examples collected in Table 6 show a dichotomy of oxazole and 1,2-diketone formation that is not fully understood so far. As mentioned above, the presence of bulky

• substituents R2 (and R3) seems to be a prerequisite of the 1,2-diketone formation, however, for the series with R2 = phenyl the observed product distributions are not easy to explain (Table 6, entries 18–23). Nevertheless, a plausible mechanism is presented in Scheme 24 showing the analogy to the Gabriel

• alternative to the strongly acidic conditions, palladium-catalyzed hydrogenolysis of the benzyloxy-substituted derivatives is possible, thus avoiding the condensation to oxazoles. Scheme 25 shows the conversion of KE52 into 1,2-diketone DK14 (compare entry 3 of Table 6). Longer reaction times lead to a

A convenient and practical synthesis of β-diketones bearing linear perfluorinated alkyl groups and a 2-thienyl moiety

• Ilya V. Taydakov,
• Yuliya M. Kreshchenova and
• Ekaterina P. Dolotova

Beilstein J. Org. Chem. 2018, 14, 3106–3111, doi:10.3762/bjoc.14.290

• -diketone 3b is known and the staring material is readily available. All the experiments were performed using about 5 mmol of compounds. The ratio of reagents was 1:1 (ketone to ester), while from 1 up to 2.5 equivalents of a base were applied. The order of reagent mixing is also significant. It was found

• that mixing 2-acetylthiophene with a base in the absence of the ester (var. A) should be avoided due to notable darkening and self-condensation of the ketone, despite Prabhu’s recommendations [25]. Similar yields of a β-diketone were obtained if the ester of perfluorocarboxylic acid was first added to

• evaporator, 60 °C, 5 Torr). The residue was pulverized in dry Ar atmosphere and dried at 0.05 Torr and 60 °C for at least 5 h. The quality of the alkoxide dramatically affects the yields of a β-diketone, while the stoichiometry is much less significant. The best results were achieved with commercial NaOMe or

One hundred years of benzotropone chemistry

• Arif Dastan,
• Haydar Kilic and
• Nurullah Saracoglu

Beilstein J. Org. Chem. 2018, 14, 1120–1180, doi:10.3762/bjoc.14.98

• selenium dioxide in boiling ethanol, followed by dehydrogenation with bromine in acetic acid at 100 °C. Another method for the synthesis of 7-hydroxy-2,3-benzotropone (241) starting from the reaction of diketone 276 with boiling acetic anhydride was achieved by Maignan (Scheme 44) [168]. The reaction of

• were catalyzed by NaOH. 5.4.2. Reaction of 4-hydroxy-2,3-benzotropone (174): The structure of 174 was confirmed by the reduction of both benzotropolone 174 and diketone 300 into the diol 305 with catalytic hydrogenation (Scheme 51) [178]. 6. Halobenzotropones 6.1. Monohalobenzotropones 6.1.1. One-step

Cross-coupling of dissimilar ketone enolates via enolonium species to afford non-symmetrical 1,4-diketones

• Keshaba N. Parida,
• Gulab K. Pathe,
• Shimon Maksymenko and
• Alex M. Szpilman

Beilstein J. Org. Chem. 2018, 14, 992–997, doi:10.3762/bjoc.14.84

• Keshaba N. Parida Gulab K. Pathe Shimon Maksymenko Alex M. Szpilman Department of Chemical Sciences, Ariel University, 4070000 Ariel, Israel 10.3762/bjoc.14.84 Abstract Due to their closely matched reactivity, the coupling of two dissimilar ketone enolates to form a 1,4-diketone remains a

• of enolates may be used to form the 1,4-diketone products in 38 to 74% yield. Due to the use of two TMS enol ethers as precursors, an optimization of the cross-coupling should include investigating the order of addition. Keywords: 1,4-diketones; enolates; enolonium species; hypervalent iodine

• = H) to afford the 1,4-diketone 7 in 71% yield (Scheme 2) [31]. We therefore focused on identifying the minimum amount of the second enolate that would lead to optimal yields and found that as little as 1.2–1.4 equiv provided the desired 1,4-diketones in acceptable yields without the need for a large

5-Aminopyrazole as precursor in design and synthesis of fused pyrazoloazines

• Ranjana Aggarwal and
• Suresh Kumar

Beilstein J. Org. Chem. 2018, 14, 203–242, doi:10.3762/bjoc.14.15

• acetic acid (Scheme 1). In the same report the other regioisomers 6-trifluoromethylpyrazolo[3,4-b]pyridines 20 were obtained under multicomponent solvent-free conditions by the reaction of hydrazine 14, β-ketonitrile 15 and β-diketone 17 as an exclusive product. The structures of both the regioisomers

• have been confirmed unambiguously by HMBC, HMQC and 19F NMR studies. The authors proposed that trifluoromethyl-β-diketone exists mainly in keto form 17 under solvent-free conditions whereas under solvent-mediated conditions the enolic form 21 towards the carbonyl carbon that carries the CF3 group is

• [2,3-e]pyrazolo[3,4-b]pyridine 77 was formed in the reaction when indandione 58 was used as β-diketone which was attributed to the loss of the benzyl fragment from 5-aminopyrazole derivative 75. Microwave-assisted reactions went to completion in very short time (5 min) compared to reactions under

Reagent-controlled regiodivergent intermolecular cyclization of 2-aminobenzothiazoles with β-ketoesters and β-ketoamides

• Irwan Iskandar Roslan,
• Kian-Hong Ng,
• Gaik-Khuan Chuah and
• Stephan Jaenicke

Beilstein J. Org. Chem. 2017, 13, 2739–2750, doi:10.3762/bjoc.13.270

• ) while good yields were obtained with β-ketoesters containing n-propyl and n-butyl moieties (Scheme 2, 3r and 3s). However, significantly lower yields were obtained with the sterically more demanding iPr group (Scheme 2, 3t). Unfortunately, β-diketone (acetylacetone) was not suitable for the reaction as