Multicomponent syntheses of pyrazoles via (3 + 2)-cyclocondensation and (3 + 2)-cycloaddition key steps

• Ignaz Betcke,
• Alissa C. Götzinger,
• Maryna M. Kornet and
• Thomas J. J. Müller

Beilstein J. Org. Chem. 2024, 20, 2024–2077, doi:10.3762/bjoc.20.178

• dihydropyridines, specifically 3,5-acyl-1,4 dihydropyridines 77, are well suited for undergoing ring opening-ring closing cyclocondensation with hydrazine in a pseudo-multicomponent reaction to give bis(pyrazolyl)methanes 78 (Scheme 28) [106]. Interestingly, the use of ester derivatives leads to the formation of

Diastereoselective synthesis of highly substituted cyclohexanones and tetrahydrochromene-4-ones via conjugate addition of curcumins to arylidenemalonates

• Deepa Nair,
• Abhishek Tiwari,
• Banamali Laha and
• Irishi N. N. Namboothiri

Beilstein J. Org. Chem. 2024, 20, 2016–2023, doi:10.3762/bjoc.20.177

• not have a significant effect on the yield or formation of respective products (Table 1, entry 12). Based on the optimization studies, a combination of KOH in toluene and TBAB (Table 1, entry 2) as phase-transfer catalyst was chosen as the best conditions. Although KOH could saponify the ester group

• predominates over saponification under our mild conditions (room temperature). Overall, the reaction proceeds smoothly without any unwanted side reactions such as saponification of the ester groups. Having optimized the reaction conditions, we proceeded to examine the substrate scope of the developed

• to the increase in electron density at the carbon β to the ester group thus inhibiting the Michael addition of curcumin (Table 2, entry 4). Arylidenemalonate 2e, bearing a weakly electron-donating substituent, reacted with 1a to afford the double Michael adduct 3e in moderate yield (46%), and the

Regioselective alkylation of a versatile indazole: Electrophile scope and mechanistic insights from density functional theory calculations

• Pengcheng Lu,
• Luis Juarez,
• Paul A. Wiget,
• Weihe Zhang,
• Krishnan Raman and
• Pravin L. Kotian

Beilstein J. Org. Chem. 2024, 20, 1940–1954, doi:10.3762/bjoc.20.170

• OPPh3 contributing to the increased error and standard deviation. Compound 6 was completely consumed and not detected (see Supporting Information File 1). Mechanistic considerations Alam and Keeting proposed a deprotonated intermediate that utilized the indazole N2 and C=O from an ester substituent at C

• system (Figure 10). Under conditions A, deprotonation and cesium coordination were heavily favored by 11.1 kcal/mol (18(N-H)). Transition states 18-N2-Cs and 18-N1-Cs were found leading to N1- and N2-products, respectively. NCIs between the cesium cation with the ester and sulfonate oxygens, and

• indazole and the deprotonated indazole was only −0.2 kcal/mol (Figure 11). Again, no preorganized intermediates were found. The NCIs were consistent with the parent system. The hydrogen bond between the H on the electrophilic methyl group and an ester oxygen was found in the transition state leading to the

Negishi-coupling-enabled synthesis of α-heteroaryl-α-amino acid building blocks for DNA-encoded chemical library applications

• Matteo Gasparetto,
• Balázs Fődi and
• Gellért Sipos

Beilstein J. Org. Chem. 2024, 20, 1922–1932, doi:10.3762/bjoc.20.168

• proceeded smoothly yielding 4j in quantitative yield. However, obtaining compound 4r presented some challenges due to the resistance of ester 2r towards conventional oxidation methods (see Table S5 in Supporting Information File 1). Consequently, a multi-step process involving ester hydrolysis and

• methods were tested and after a brief optimization process, zinc dust and HCl in a mixture of EtOH/dioxane proved to be the best conditions in order to maximize the yield and limit the amino ester instability issues (see Table S6 in Supporting Information File 1). By slightly adjusting the reaction time

• first attached to carboxylic acid functionalized DNA headpiece 7a (first reverse amidation). Next, the ester was hydrolyzed to obtain acid 9, and finally, a second reverse amidation with aniline afforded 10. Both the reverse amidation and the ester hydrolysis were performed following literature

Access to 2-oxoazetidine-3-carboxylic acid derivatives via thermal microwave-assisted Wolff rearrangement of 3-diazotetramic acids in the presence of nucleophiles

• Ivan Lyutin,
• Vasilisa Krivovicheva,
• Grigory Kantin and
• Dmitry Dar’in

Beilstein J. Org. Chem. 2024, 20, 1894–1899, doi:10.3762/bjoc.20.164

• -methoxyethylamine. Attempts to obtain directly 2-oxoazetidine carboxylic acid (or its decarboxylation product) or its trifluoroethyl ester by running the synthesis with water or trifluoroethanol were also unsuccessful. Acylation of the π-excessive double bonds of N-alkylindole and dihydropyran by the in situ

The Groebke–Blackburn–Bienaymé reaction in its maturity: innovation and improvements since its 21st birthday (2019–2023)

• Cristina Martini,
• Muhammad Idham Darussalam Mardjan and
• Andrea Basso

Beilstein J. Org. Chem. 2024, 20, 1839–1879, doi:10.3762/bjoc.20.162

• ester) was positioned in the aldehyde precursors 86 (Scheme 28). Various 2-aminothiazoles 87 and tert-butyl isocyanide (5) were reacted with 86 in the presence of Yb(OTf)3, affording 88. Addition of a new aliquot of Yb(OTf)3 (30 mol %) allowed the new ring formation through a 7-exo-trig intramolecular

Chiral bifunctional sulfide-catalyzed enantioselective bromolactonizations of α- and β-substituted 5-hexenoic acids

• Sao Sumida,
• Ken Okuno,
• Taiki Mori,
• Yasuaki Furuya and
• Seiji Shirakawa

Beilstein J. Org. Chem. 2024, 20, 1794–1799, doi:10.3762/bjoc.20.158

• -valerolactones 7 and 8, which are functionalized with sulfur and nitrogen, in high yields. Additionally, optically active δ-valerolactone 3a was converted to optically active epoxy-ester 9 upon treatment with potassium carbonate in methanol. Notably, the transformed products were obtained without any loss of

Syntheses and medicinal chemistry of spiro heterocyclic steroids

• Laura L. Romero-Hernández,
• Ana Isabel Ahuja-Casarín,
• Penélope Merino-Montiel,
• Sara Montiel-Smith,
• José Luis Vega-Báez and
• Jesús Sandoval-Ramírez

Beilstein J. Org. Chem. 2024, 20, 1713–1745, doi:10.3762/bjoc.20.152

• diazo precursor. To achieve this, cholesterol was first esterificated using 2-(4-methoxyphenyl)acetic acid and DCC. The resulting arylacetic ester 12 was then reacted with 4-acetamidobenzenesulfonyl azide (p-ABSA) and DBU in anhydrous acetonitrile to yield the diazo compound 13 in 22% yield. The carbene

• final CO insertion to release the ester. After an acid hydrolysis which produced 36, a basic treatment induced the condensation reaction to yield the heterocycle 37 in 99% yield. This reaction sequence was also applied to the acetates of ethisterone and ethynylestradiol, resulting in similar yields in

• ester under basic conditions was carried out, followed by the transformation of the carboxyl group to the amides 165 and 166 by treatment with thionyl chloride and the corresponding amine. Tetraoxanes were obtained from ketones 163, 165, and 166 by a peroxyacylation reaction using an acidic hydrogen

Chemo-enzymatic total synthesis: current approaches toward the integration of chemical and enzymatic transformations

• Ryo Tanifuji and
• Hiroki Oguri

Beilstein J. Org. Chem. 2024, 20, 1693–1712, doi:10.3762/bjoc.20.151

• Suzuki–Miyaura coupling with boronic ester 53 and O-acetylation furnished 54. The dienophile component, morachalcone A (44), was synthesized from phenol 55 in four steps including O-prenylation and subsequent Claisen rearrangement, aldol condensation with 56, and deprotection. The key chemo-enzymatic

• this problem, the research group designed synthetic substrate analogs (96, 101) that mimic the biosynthetic intermediate 88 (Scheme 10A). By replacing an amide linkage in 88 with an ester linkage, the fatty acid side chain could be removed under mild conditions after enzymatic construction of the

• pentacyclic secondary amine 97 bearing the ester linker in the C1 side chain in one pot. After removal of SfmC by precipitation and centrifugation, the reaction mixture containing secondary amine 97 was subjected to the reductive amination using 2-picoline borane as a hydride source, yielding tertiary amine

Methyltransferases from RiPP pathways: shaping the landscape of natural product chemistry

• Maria-Paula Schröder,
• Isabel P.-M. Pfeiffer and
• Silja Mordhorst

Beilstein J. Org. Chem. 2024, 20, 1652–1670, doi:10.3762/bjoc.20.147

• ]. Further O-MTs can be classified based on a common acceptor group of modification, namely C-terminal carboxy-MTs and peptide/protein ʟ-aspartyl O-MTs (PAMTs). C-terminal carboxymethyltransferases Carboxy-MTs catalyse the formation of a methyl ester by methylating the oxygen atom within the hydroxy group of

• enzyme engineering and rational design [73][74]. Lentzea kentuckyensis sp. produces lassomycin (Figure 4), a lasso peptide, with a methyl ester at the C-terminus. The las cluster encodes LasF, which is predicted to function as an O-MT. Since no other putative MT is encoded in the las cluster, LasF is

• proposed to methylate lassomycin [77]. PAMTs – peptide/protein ʟ-aspartyl O-methyltransferases PAMTs share a conserved C-terminal domain, substantial sequence homology, and a common enzymatic activity. They catalyse the conversion between aspartate and isoaspartate with aspartyl-O-methyl ester and

Polymer degrading marine Microbulbifer bacteria: an un(der)utilized source of chemical and biocatalytic novelty

• Weimao Zhong and
• Vinayak Agarwal

Beilstein J. Org. Chem. 2024, 20, 1635–1651, doi:10.3762/bjoc.20.146

• . Their structures differ from common parabens by the presence of an acetamide group ortho to the phenolic hydroxy group [14]. They exhibited weak activity against E. coli and methicillin-sensitive Staphylococcus aureus (MSSA). The three analogues 15–17 (Figure 6) with different ester chain lengths were

• synthesized and tested for antimicrobial activity. However, no clear trend was found between the ester length and bioactivity. In addition to the paraben derivatives, three known nucleosides, 4´,5´-didehydro-5´-deoxyinosine (18), 2´-O-methyladenosine (19), and 5´-methylthioinosine (20) were also identified

Supramolecular assemblies of amphiphilic donor–acceptor Stenhouse adducts as macroscopic soft scaffolds

• Ka-Lung Hung,
• Leong-Hung Cheung,
• Yikun Ren,
• Ming-Hin Chau,
• Yan-Yi Lam,
• Takashi Kajitani and
• Franco King-Chi Leung

Beilstein J. Org. Chem. 2024, 20, 1590–1603, doi:10.3762/bjoc.20.142

• nitrogen atmosphere, followed by reduction of the indole motif in compound 1n to indoline in 2n. The ester group in compound 2n was deprotected under basic conditions to give compound 3n (Scheme 2). DAn with different chain lengths of the alkyl linker were synthesized through an aza-Piancatalli

Electrocatalytic hydrogenation of cyanoarenes, nitroarenes, quinolines, and pyridines under mild conditions with a proton-exchange membrane reactor

• Koichi Mitsudo,
• Atsushi Osaki,
• Haruka Inoue,
• Eisuke Sato,
• Naoki Shida,
• Mahito Atobe and
• Seiji Suga

Beilstein J. Org. Chem. 2024, 20, 1560–1571, doi:10.3762/bjoc.20.139

• yields (7a–e, 7g, and 7h), except for 6f which contained a methyl group at the 4-position. The reaction of 2,3-dimethylquinoline (6i) gave the desired product 7i (cis/trans = 3:1) in 77% yield. Substrates bearing acetyl (6k), ester (6l), and amide (6m) groups were tolerated under these conditions and

Benzylic C(sp³)–H fluorination

• Alexander P. Atkins,
• Alice C. Dean and
• Alastair J. J. Lennox

Beilstein J. Org. Chem. 2024, 20, 1527–1547, doi:10.3762/bjoc.20.137

• yields, with the authors proposing that HFIP aided in stabilising the electrochemically generated benzylic radical cation intermediates. Secondary and tertiary benzylic substrates bearing halogen, ester, protected amine and alkyl functional groups tolerated the reaction conditions well. The authors

• showed they were able to scale-up and selectively fluorinate the ibuprofen methyl ester at the methylene group to produce over 2 g of product 12. The utility of the benzyl fluoride products as strategic intermediates for benzylation of electron-rich arenes was demonstrated by the authors (Figure 41B

Towards an asymmetric β-selective addition of azlactones to allenoates

• Behzad Nasiri,
• Ghaffar Pasdar,
• Paul Zebrowski,
• Katharina Röser,
• David Naderer and
• Mario Waser

Beilstein J. Org. Chem. 2024, 20, 1504–1509, doi:10.3762/bjoc.20.134

• investigated the generality of this protocol. As outlined in Scheme 2, differently substituted allenoates were reasonably well tolerated (see products 5a–d), albeit some erosion in enantioselectivity was observed when using a tert-butyl ester containing allenoate (product 5d). Various α-arylmethyl-substituted

Electrophotochemical metal-catalyzed synthesis of alkylnitriles from simple aliphatic carboxylic acids

• Yukang Wang,
• Yan Yao and
• Niankai Fu

Beilstein J. Org. Chem. 2024, 20, 1497–1503, doi:10.3762/bjoc.20.133

• size of the alkyl side chain at the alpha position of arylacetic acids (9–16). These features offer great opportunities for the introduction of a wide range of functional groups, including bromide (9), boron (12), ether (13), nitrile (14), ester (15), and alkene (16) moieties, which are versatile

Challenge N- versus O-six-membered annulation: FeCl₃-catalyzed synthesis of heterocyclic N,O-aminals

• Giacomo Mari,
• Lucia De Crescentini,
• Gianfranco Favi,
• Fabio Mantellini,
• Diego Olivieri and
• Stefania Santeusanio

Beilstein J. Org. Chem. 2024, 20, 1412–1420, doi:10.3762/bjoc.20.123

• ), whose sequential acylation process by iso(thio)cyanates 3a–h gives rise to the asymmetric (thio)urea derivatives (intermediate II). The spontaneous nucleophilic attack of the (thio)amide nitrogen on the terminal methyl ester function at C-4 of the starting azo-ene system provides a regioselective

Hypervalent iodine-catalyzed amide and alkene coupling enabled by lithium salt activation

• Akanksha Chhikara,
• Fan Wu,
• Navdeep Kaur,
• Prabagar Baskaran,
• Alex M. Nguyen,
• Zhichang Yin,
• Anthony H. Pham and
• Wei Li

Beilstein J. Org. Chem. 2024, 20, 1405–1411, doi:10.3762/bjoc.20.122

• , ester, and phthalimide proceeded smoothly with good yields and excellent regioselectivities to access the oxazoline products as single regioisomers (Figure 3, products 18–22). The o-bromo-substituted styrene also afforded the corresponding product 23. Furthermore, 1,1-di-substituted α-methylstyrene and

Synthesis of substituted triazole–pyrazole hybrids using triazenylpyrazole precursors

• Simone Gräßle,
• Laura Holzhauer,
• Nicolai Wippert,
• Olaf Fuhr,
• Martin Nieger,
• Nicole Jung and
• Stefan Bräse

Beilstein J. Org. Chem. 2024, 20, 1396–1404, doi:10.3762/bjoc.20.121

• benzylic residues differed depending on the benzylic residue's functional groups and the pyrazole substitution pattern. For starting materials 15a and 15d, an excess of product 17 was usually observed. With the ester-functionalized triazene 15c and m-substituted benzylic reagents, regioisomer 18 was the

Synthetic applications of the Cannizzaro reaction

• Bhaskar Chatterjee,
• Dhananjoy Mondal and
• Smritilekha Bera

Beilstein J. Org. Chem. 2024, 20, 1376–1395, doi:10.3762/bjoc.20.120

• % enantioselectivity. They employed a double asymmetric induction with (+)/(−)-menthol (12), and CuX2 bis(oxazoline) catalyst where the corresponding chiral mandelate ester 13 was obtained in 81% yield and high selectivity (90% de) (Scheme 6). The proposed mechanism of the reaction is depicted below. Hong et al

• modern modifications using mild and sustainable reagents, solvents, advanced instrumental techniques, and catalysts in both intramolecular and intermolecular versions of the reaction have made the Cannizzaro reaction an important tool for the synthesis of diverse molecules containing alcohol, acid, ester

Generation of alkyl and acyl radicals by visible-light photoredox catalysis: direct activation of C–O bonds in organic transformations

• Mithu Roy,
• Bitan Sardar,
• Itu Mallick and
• Dipankar Srimani

Beilstein J. Org. Chem. 2024, 20, 1348–1375, doi:10.3762/bjoc.20.119

• )], regenerating the [Ir(III)] catalyst and completing the catalytic cycle. Overman and co-workers [50] used tert-alkyl N-phthalimidoyl oxalates to produce alkyl radicals that were further reacted with various Michael acceptors (Scheme 13). The photocatalyst Ru(bpy)32+ and Hantzsch ester were essential for the

• excitation of [Ir(III)] to activated *[Ir(III)], which is then reduced by Hantzsch ester to form [Ir(II)]. After SET, the resultant [Ir(II)] species reduces N-alkoxyphthalimide to produce the N-alkoxyphthalimide radical anion. The Hantzsch ester radical cation further protonates this anion, promoting

• the production of an alkyl radical. After that, this alkyl radical reacts with allyl and alkenyl sulfones in an addition–elimination cycle to produce the required product and a benzenesulfonyl radical. The benzenesulfonyl radical abstracts a hydrogen radical from the Hantzsch ester radical to form

Synthesis of indano[60]fullerene thioketone and its application in organic solar cells

• Yong-Chang Zhai,
• Shimon Oiwa,
• Shinobu Aoyagi,
• Shohei Ohno,
• Tsubasa Mikie,
• Jun-Zhuo Wang,
• Hirofumi Amada,
• Koki Yamanaka,
• Kazuhira Miwa,
• Naoyuki Imai,
• Takeshi Igarashi,
• Itaru Osaka and
• Yutaka Matsuo

Beilstein J. Org. Chem. 2024, 20, 1270–1277, doi:10.3762/bjoc.20.109

• derivatives with an emphasis on tuning solubility and energy levels. Meanwhile, less attention has been devoted to improving the thermal stability of fullerene derivatives. One well-known example is [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), which is recognized for its excellent solubility in solution

Domino reactions of chromones with activated carbonyl compounds

• Peter Langer

Beilstein J. Org. Chem. 2024, 20, 1256–1269, doi:10.3762/bjoc.20.108

• to the chromone and ring cleavage to give intermediate I. Subsequent Knoevenagel reaction by attack of the methylene carbon to the carbonyl group adjacent to the ester group resulted in the formation of the final products. The regioselective cyclization can be explained by the higher electrophilicity

• of the carbonyl group adjacent to the ester, due to the electron-withdrawing effect of the latter. The yields were generally good to very good and no trend was observed depending on the structure of the chromones. 1,3-Diphenylacetone Similarly, reaction of 1,3-diphenylacetone (4) with 11a,d afforded

• observed under these conditions, because the electron-withdrawing character of the additional ester group which destabilizes formation of a cation at the neighboring position. The yields were in most cases moderate (42–54%). Two products were obtained in higher yields (71 and 80%). However, no clear trend

Competing electrophilic substitution and oxidative polymerization of arylamines with selenium dioxide

• Vishnu Selladurai and
• Selvakumar Karuthapandi

Beilstein J. Org. Chem. 2024, 20, 1221–1235, doi:10.3762/bjoc.20.105

• . It crystallized in a triclinic crystal system in the space group P−1. It was structurally similar to the other oxamides 3 and 9. It showed an intramolecular hydrogen bonding between the NH and the carbonyl group of the methoxy ester. A layer-by-layer packing was observed in the crystal structure

• (Figure S37, Supporting Information File 1). The dipolar characteristics of the ester group appeared to assist the molecular layer-by-layer stacking seen in the crystal packing. The molecular structure of the quinone derivative 10 is shown in Figure 4. It crystallized in a monoclinic crystal system in the

Manganese-catalyzed C–C and C–N bond formation with alcohols via borrowing hydrogen or hydrogen auto-transfer

• Mohd Farhan Ansari,
• Atul Kumar Maurya,
• Abhishek Kumar and
• Saravanakumar Elangovan

Beilstein J. Org. Chem. 2024, 20, 1111–1166, doi:10.3762/bjoc.20.98

• )phosphine ligand (PN3P) (Mn3) and studied N-methylation reactions in the presence of t-BuOK (20 mol %) at 120 °C for 24 h in toluene [36]. This catalytic system tolerated various functional groups, including nitro, ester, amide, and ketones and gave moderate to good yields (42–98%) of the mono-N-methylated

• moderate-to-high yields with aliphatic and aromatic alcohols (Scheme 18). In addition, this protocol allowed for the synthesis of indole through an intramolecular reaction and a resveratrol-derived amine. However, this catalytic method did not tolerate some functional groups such as nitro, ester, and

• heterocyclic alcohols were tested and showed good functional group tolerances. However, ester and nitrile-substituted ketones were not alkylated with this protocol. The proposed mechanism showed that the Mn(CO)5Br reacted with ligand L3 to generate the active complex Mn-L3-I in the presence of a base. The