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

• compounds 38 are also interesting building blocks in pyrazole synthesis. Through the reaction of 1,5-diaryl-1,3,5-pentanetriones 38 with hydrazines, Knorr synthesis of pyrazoles and Fischer indole synthesis can be combined in a pseudo-three-component fashion to give 5-(indol-3-yl)pyrazoles 39 (Scheme 11

Harnessing the versatility of hydrazones through electrosynthetic oxidative transformations

• Aurélie Claraz

Beilstein J. Org. Chem. 2024, 20, 1988–2004, doi:10.3762/bjoc.20.175

• versatile reagents in organic synthesis. They have for instance been frequently employed for the construction of azacycles through various cyclization protocols or cycloaddition reactions [6][7][8][9][10]. Early work in this field includes the well-known Fischer indole synthesis [11]. Additionally, they

Consecutive four-component synthesis of trisubstituted 3-iodoindoles by an alkynylation–cyclization–iodination–alkylation sequence

• Nadia Ledermann,
• Alae-Eddine Moubsit and
• Thomas J. J. Müller

Beilstein J. Org. Chem. 2023, 19, 1379–1385, doi:10.3762/bjoc.19.99

• [9][10][11] and their preparation is an evergreen in organic synthesis [12][13][14][15]. Although the classical Fischer indole synthesis provides a very reliable and broadly applicable access to indole derivatives [16][17][18], striving for new indole syntheses is ongoing. In particular, metal

New synthesis of a late-stage tetracyclic key intermediate of lumateperone

• Mátyás Milen,
• Bálint Nyulasi,
• Tamás Nagy,
• Gyula Simig and
• Balázs Volk

Beilstein J. Org. Chem. 2022, 18, 653–659, doi:10.3762/bjoc.18.66

• a Fischer indole synthesis. The inexpensive starting material, the efficient synthetic steps, and the avoidance of the borane-based reduction step provide a reasonable potential for scalability. Keywords: drug substance; indole synthesis; key intermediate; protecting group; telescoping

• to the hydrazine derivative 4, followed by a Fischer indole synthesis with ethyl 4-oxopiperidine-1-carboxylate (5) provided tetracyclic compound 6. Its reduction with sodium cyanoborohydride in trifluoroacetic acid (TFA) to cis-indoline derivative (±)-7, followed by N-methylation [(±)-8] and

• transformed into N-nitroso derivative 32 by treatment with sodium nitrite in aqueous acetic acid. The next two steps, reduction of the nitroso group to hydrazine derivative 33 and its coupling with piperidinone 5 in a Fischer indole synthesis, were telescoped to form tetracyclic product 34. The latter was

Ready access to 7,8-dihydroindolo[2,3-d][1]benzazepine-6(5H)-one scaffold and analogues via early-stage Fischer ring-closure reaction

• Irina Kuznetcova,
• Felix Bacher,
• Daniel Vegh,
• Hsiang-Yu Chuang and
• Vladimir B. Arion

Beilstein J. Org. Chem. 2022, 18, 143–151, doi:10.3762/bjoc.18.15

• -phenylhydrazine in acetic acid that delivers methyl 2-(1-benzyl-3-(2-nitrophenyl)-1H-indol-2-yl)acetate in 55% yield. Keywords: anticancer; Fischer indole synthesis; Heck reaction; heterocyclic compounds; indolobenzazepines; latonduines; paullones; Introduction Indolobenzazepines are fused heterocyclic

• as the key intermediate. The third pathway (c) was centered around a ring-closure reaction via lactam-bond formation from a precursor that contains a carboxylic ester in position 2 and an o-aniline moiety in position 3 of the indole ring by Fischer indole synthesis from methyl 4-(2-nitrophenyl)-3

• ) was confirmed by the successful preparation of two closely related analogues, namely 3b, bearing a bromo substituent at position 11 of the backbone C (Scheme 6), and 3c, with an 8-membered azocinone ring instead of the 7-membered one. The synthesis of 3b started with a Fischer indole synthesis from

Catalyzed and uncatalyzed procedures for the syntheses of isomeric covalent multi-indolyl hetero non-metallides: an account

• Ranadeep Talukdar

Beilstein J. Org. Chem. 2021, 17, 2102–2122, doi:10.3762/bjoc.17.137

• only, thus stating the requirement of acid for this Fischer indole synthesis. Elemental sulfur has also been utilized in preparing bis(indol-3-yl)sulfides under transition-metal compound catalyzed spontaneous oxidation of the central chalcogen atom. Such reactions were carried out by Shibahara (2014

• . Synthesis of bis(indol-3-yl)sulfides using N-silylated 3-bromoindole 93. Fischer indole synthesis of bis(indol-3-yl)sulfides using thio diketones. Oxidative synthesis of bis(indol-3-yl)sulfides using indoles and elemental sulfur. Synthesis of bis(indol-3-yl)sulfides using sulfoxides as sulfur source

Synthesis of 1-indolyl-3,5,8-substituted γ-carbolines: one-pot solvent-free protocol and biological evaluation

• Premansh Dudhe,
• Mena Asha Krishnan,
• Kratika Yadav,
• Diptendu Roy,
• Krishnan Venkatasubbaiah,
• Biswarup Pathak and
• Venkatesh Chelvam

Beilstein J. Org. Chem. 2021, 17, 1453–1463, doi:10.3762/bjoc.17.101

• decomposition of N-pyridylbenzotriazoles. Later, the reaction conditions were modified to make this reaction more versatile and operationally simple such as by the use of microwave irradiation [12]. Meanwhile, the Fischer indole synthesis was successfully extended for the synthesis of significant biologically

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

• antibacterial, antifungal, anticancer, or anti-inflammatory agents or even on the central nervous system [7][12][13]. Several routes have been reported to access these key compounds, the most developed being for the indole [14] derivatives using the Fischer indole synthesis involving sigmatropic rearrangements

Design and synthesis of diazine-based panobinostat analogues for HDAC8 inhibition

• Sivaraman Balasubramaniam,
• Sajith Vijayan,
• Liam V. Goldman,
• Xavier A. May,
• Kyra Dodson,
• Sweta Adhikari,
• Fatima Rivas,
• Davita L. Watkins and
• Shana V. Stoddard

Beilstein J. Org. Chem. 2020, 16, 628–637, doi:10.3762/bjoc.16.59

• acrylate aldehyde 9 in 61% yield. The next step involved the crucial reductive amination reaction between aldehyde 9 with indolamine 10, which had been obtained via Fischer indole synthesis – the reaction of phenylhydrazine with 5-chloro-2-pentanone [35]. Initial reduction attempts using sodium

Synthesis of aryl-substituted thieno[3,2-b]thiophene derivatives and their use for N,S-heterotetracene construction

• Nadezhda S. Demina,
• Nikita A. Kazin,
• Nikolay A. Rasputin,
• Roman A. Irgashev and
• Gennady L. Rusinov

Beilstein J. Org. Chem. 2019, 15, 2678–2683, doi:10.3762/bjoc.15.261

• ketones were used to synthesize new N,S-heterotetracenes, namely 9H-thieno[2',3':4,5]thieno[3,2-b]indoles by their treatment with arylhydrazines in accordance with the Fischer indolization reaction. Keywords: Fiesselmann thiophene synthesis; Fischer indole synthesis; N,S-heteroacene; thieno[3,2-b

A speedy route to sterically encumbered, benzene-fused derivatives of privileged, naturally occurring hexahydropyrrolo[1,2-b]isoquinoline

• Olga Bakulina,
• Alexander Ivanov,
• Vitalii Suslonov,
• Dmitry Dar’in and
• Mikhail Krasavin

Beilstein J. Org. Chem. 2017, 13, 1413–1424, doi:10.3762/bjoc.13.138

• non-classical inputs for the Joullié–Ugi reaction and for subsequent preparation [28] of sterically encumbered, constrained peptidomimetic frameworks. Diversely substituted indolenines 9 are easy to prepare via the Fischer indole synthesis [26] and their use in the CCR can be expected to result in

Synthesis of constrained analogues of tryptophan

• Elisabetta Rossi,
• Valentina Pirovano,
• Marco Negrato,
• Giorgio Abbiati and
• Monica Dell’Acqua

Beilstein J. Org. Chem. 2015, 11, 1997–2006, doi:10.3762/bjoc.11.216

• from the biological evaluation to the chemistry of tryptophan analogues, the above described two categories were synthesized according to the Pictet–Spengler reaction or by Fischer indole synthesis [11][12][13][14]. However, Fischer indolization suffers from the lack of regioselectivity depending on

• intermolecular [4 + 2]-cycloaddition of 2-vinylindoles and methyl 2-acetamidoacrylate. Although the reaction requires a stoichiometric amount of EtAlCl2 as promoter, it presents several advantages with respect to classical Fischer indole synthesis, normally adopted for the preparation of these derivatives [11

Synthesis and biological activity of N-substituted-tetrahydro-γ-carbolines containing peptide residues

• Nadezhda V. Sokolova,
• Valentine G. Nenajdenko,
• Vladimir B. Sokolov,
• Daria V. Vinogradova,
• Elena F. Shevtsova,
• Ludmila G. Dubova and
• Sergey O. Bachurin

Beilstein J. Org. Chem. 2014, 10, 155–162, doi:10.3762/bjoc.10.13

• hydrochlorides and N-substituted 4-piperidones using Fischer indole synthesis [12][13]. Propargyl acrylate (2) was obtained from propargyl alcohol and acryloyl chloride according to procedure described in [25]. General procedure for the synthesis of compounds 3a–d: A mixture of correspondingly substituted

One-step synthesis of pyridines and dihydropyridines in a continuous flow microwave reactor

• Mark C. Bagley,
• Vincenzo Fusillo,
• Robert L. Jenkins,
• M. Caterina Lubinu and
• Christopher Mason

Beilstein J. Org. Chem. 2013, 9, 1957–1968, doi:10.3762/bjoc.9.232

• synthetic transformations (Scheme 1), including Bohlmann–Rahtz cyclodehydration of aminodienones 1 to the corresponding pyridines 2 [44][45], Fischer indole synthesis of tetrahydrocarbazole 5 from phenylhydrazine (3) and cyclohexanone (4) [44], and hydrolysis of 4-chloromethylthiazole (6) to give the

Simple synthesis of pyrrolo[3,2-e]indole-1-carbonitriles

• Adam Trawczyński,
• Robert Bujok,
• Zbigniew Wróbel and
• Krzysztof Wojciechowski

Beilstein J. Org. Chem. 2013, 9, 934–941, doi:10.3762/bjoc.9.107

• cyanoborohydride [4]. On the other hand there are many methods of synthesis of pyrrolo[3,2-e]indoles such as the copper-catalyzed transformation of tetrahydroquinoline derivatives [4], photochemical cyclization of 1,2-bis(2-pyrrolo)ethylenes [5], the Fischer indole synthesis from indol-5-ylhydrazones [3], or a

Synthesis of diverse indole libraries on polystyrene resin – Scope and limitations of an organometallic reaction on solid supports

• Kerstin Knepper,
• Sylvia Vanderheiden and
• Stefan Bräse

Beilstein J. Org. Chem. 2012, 8, 1191–1199, doi:10.3762/bjoc.8.132

• ]. Organometallic reactions on solid supports are always particularly challenging [25]. In the past, indoles were synthesized by using, for example, Fischer indole synthesis [26][27][28][29][30], Bartoli indole synthesis, Nenitzescu synthesis [31], Wittig indole synthesis [32], Madelung indole synthesis [33

An intramolecular inverse electron demand Diels–Alder approach to annulated α-carbolines

• Zhiyuan Ma,
• Feng Ni,
• Grace H. C. Woo,
• Sie-Mun Lo,
• Philip M. Roveto,
• Scott E. Schaus and
• John K. Snyder

Beilstein J. Org. Chem. 2012, 8, 829–840, doi:10.3762/bjoc.8.93

• prepare anilinopyridines, with final indole ring closure occurring by either a second cross-coupling [45] or a photocyclization [46]. The former, sequential cross-coupling strategy closely follows the previous work by Queguiner [47]. A Fischer indole synthesis route through the 2-pyridylhydrazone of

An overview of the key routes to the best selling 5-membered ring heterocyclic pharmaceuticals

• Marcus Baumann,
• Ian R. Baxendale,
• Steven V. Ley and
• Nikzad Nikbin

Beilstein J. Org. Chem. 2011, 7, 442–495, doi:10.3762/bjoc.7.57

• , as well as psychedelic agents. Indole is also one of the best represented heterocyclic motifs present in the top selling pharmaceuticals, being found in eight of the top 200 drugs, with five of these belonging to the triptan family of antimigraine treatments. The classical Fischer indole synthesis is

• usually reported as one of the first choice routes to prepare these scaffolds. Drugs such as GSK’s serotonin receptor modulators sumatriptan (49, Imitrex) and zolmitriptan (50, Zomig) use the Fischer indole synthesis at a late stage in order to form the desired compound albeit in only low to moderate

• has been replaced by an oxazolinone ring. The original synthesis utilised 4-nitro-L-phenylalanine (73) as the precursor for the oxazoline moiety (Scheme 16) [19]. The resulting Fischer indole synthesis is similar to that used for sumatriptan (Scheme 9). More recent reports [20] deal with improvements