Deuterated reagents in multicomponent reactions to afford deuterium-labeled products

• Kevin Schofield,
• Shayna Maddern,
• Yueteng Zhang,
• Grace E. Mastin,
• Rachel Knight,
• Wei Wang,
• James Galligan and
• Christopher Hulme

Beilstein J. Org. Chem. 2024, 20, 2270–2279, doi:10.3762/bjoc.20.195

• is comprised of reaction of an isonitrile, amine, and aldehyde/ketone, in the presence of phenylphosphinic acid (PPA), to give α-amino amides [35]. Examples of deuterated Ugi-3CR products are represented in Scheme 4. Like the Ugi 4-CR reaction, there was no deuterium scrambling in the Ugi 3-CR. Using

A facile three-component route to powerful 5-aryldeazaalloxazine photocatalysts

• Ivana Weisheitelová,
• Radek Cibulka,
• Marek Sikorski and
• Tetiana Pavlovska

Beilstein J. Org. Chem. 2024, 20, 1831–1838, doi:10.3762/bjoc.20.161

• aldehydes and N-methylbarbituric acid in AcOH/PPA (polyphosphoric acid). However, this method was not successful for the synthesis of 5-aryldeazaalloxazines 2, and we never observed the formation of 5,10-dihydropyrimido[4,5-b]quinolinediones either. We noticed that the chemical nature of the solvent was

• was significantly enhanced when refluxing in DMF with a catalytic amount of AlCl3 compared to the reaction in clear DMF (Table 1, entries 7–9). Other Lewis acids were not as effective, except for a combination of DMSO/TMSOTf (Table 1, entry 4). The application of AcOH/PPA for the synthesis of 5

Thienothiophene-based organic light-emitting diode: synthesis, photophysical properties and application

• Recep Isci and
• Turan Ozturk

Beilstein J. Org. Chem. 2023, 19, 1849–1857, doi:10.3762/bjoc.19.137

• polyphosphoric acid (PPA) in refluxing chlorobenzene to give 3 (TT) in 86% yield. The brominated TT 4 was obtained through selective monobromination of compound 3 using NBS at −10 °C in DMF in 88% yield. The boronated triphenylamine 6 was constructed in a one-pot two-step reaction in 77% yield, by lithiation of

• nitrogen flow. Materials 3-Bromothiophene (97%, Across), 2-bromo-4′-methoxyacetophenone (97% Merck), N-bromosuccinimide (Sigma-Aldrich), polyphosphoric acid (PPA, 115% H3PO4 basis, Sigma-Aldrich), n-butyllithium (2.5 M in hexanes, Sigma-Aldrich), sodium sulfate (Merck), 4-bromotriphenylamine (Sigma-Aldrich

Strategies in the synthesis of dibenzo[b,f]heteropines

• David I. H. Maier,
• Barend C. B. Bezuidenhoudt and
• Charlene Marais

Beilstein J. Org. Chem. 2023, 19, 700–718, doi:10.3762/bjoc.19.51

• [36] via the polyphosphoric acid (PPA) catalysed cyclisation of 2,2'-diaminobibenzyl (20) at elevated temperatures (Scheme 3) [37][38]. 1.3 Catalytic dehydrogenation An early synthesis of 5H-dibenzo[b,f]azepine (1a) involved the gas phase dehydrogenation of 10,11-dihydro-5H-dibenzo[b,f]azepine (2a) to

•  8). 2.4 Ring expansion of N-arylindoles (41) The polyphosphoric acid (PPA)-catalysed rearrangement of N-arylindoles 41 was first reported by Tokmakov and Grandberg [48]. The reaction provided moderate yields with a simple 2 step linear sequence from indole 39. The reaction requires heating at

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

• addition between nitrostyrene adducts A and β-keto enamine B generated in situ consequently undergoes cyclization C and dehydration D to afford the desired product 62. PPA-SiO2 accelerates the reaction by enhancing the electrophilicity of the 1,3-diketones and the aldehydes by increasing the rate of

• generation of the β-enaminocarbonyl and nitrostyrene intermediates. Activation of Michael addition followed cyclization was catalyzed by silica-supported PPA-SiO2 (Scheme 23). Fused pyrroles have also been constructed by exploring the utility of a multicomponent reaction coupled with microwave irradiation

Synthesis of imidazo[1,5-a]pyridines via cyclocondensation of 2-(aminomethyl)pyridines with electrophilically activated nitroalkanes

• Dmitrii A. Aksenov,
• Nikolai A. Arutiunov,
• Vladimir V. Maliuga,
• Alexander V. Aksenov and
• Michael Rubin

Beilstein J. Org. Chem. 2020, 16, 2903–2910, doi:10.3762/bjoc.16.239

• , USA 10.3762/bjoc.16.239 Abstract Imidazo[1,5-a]pyridines were efficiently prepared via the cyclization of 2-picolylamines with nitroalkanes electrophilically activated in the presence of phosphorous acid in polyphosphoric acid (PPA) medium. Keywords: cyclization; heterocycles; imidazo[1,5-a

• ][37]. However, given the importance of these targets, new preparative methods are still in high demand. Herein we demonstrate a new synthetic approach towards imidazo[1,5-a]pyridines, taking advantage of the unusual electrophilic properties of nitroalkanes activated by PPA. Results and Discussion

• equiv) was heated at 110 °C with 85% PPA for 30 min, and 2-(aminomethyl)pyridine (12) was added in small portions. After 3 h of stirring at 110 °C, the reaction mixture was quenched with ice-cold water, neutralized with aqueous ammonia, and extracted with ethyl acetate. The organic layer was analyzed by

Microwave-assisted synthesis of 2-substituted 4,5,6,7-tetrahydro-1,3-thiazepines from 4-aminobutanol

• María C. Mollo,
• Natalia B. Kilimciler,
• Juan A. Bisceglia and
• Liliana R. Orelli

Beilstein J. Org. Chem. 2020, 16, 32–38, doi:10.3762/bjoc.16.5

• reactions in either case. The synthesis of 2-phenyl-4,5,6,7-tetrahydro-1,3-thiazepine by cyclodehydration of N-(4-hydroxybutyl)thiobenzamide was attempted with different condensing agents: PPA (100 °C, 15 h), Burgess (25 °C, 48 h) and PEG-Burgess (80 °C, 2 h) reagents, and under Mitsunobu conditions. In the

• Mitsunobu conditions led exclusively to the pyrrolidine derivative (76%) [32]. Therefore, the few literature examples reported until now are either complicated by side reactions or involve long reaction times and/or modest yields. Polyphosphoric acid (PPA) esters PPE (ethyl polyphosphate) and PPSE

• -toxic and environmentally safe. These reagents play a dual role, as they enhance the electrophilicity of nitriles, carbonyls and carbinols, and can also react irreversibly with water. Unlike PPA, a Brønsted acid incompatible with some acid-sensitive functionalities, PPE and PPSE are aprotic and mild

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

• -substituted oxazole derivatives OX. Hydrogenolyses of benzyloxy-substituted β-ketoenamides KE52 and KE54 to 1,2-diketone DK14 and to diastereomeric α-hydroxy-β-amino ketones 9. Conversions of 2,4-dicyclopropyl-substituted oxazole OX7 into oxazole derivatives OX18–20 (PPA = polyphosphoric acid). Syntheses of

Synthesis of dihydroquinazolines from 2-aminobenzylamine: N³-aryl derivatives with electron-withdrawing groups

• Nadia Gruber,
• Jimena E. Díaz and
• Liliana R. Orelli

Beilstein J. Org. Chem. 2018, 14, 2510–2519, doi:10.3762/bjoc.14.227

• , which are able at the same time, to activate nitrogen and oxygen functionalities towards nucleophilic attack. This dual behavior makes them valuable reagents, capable of promoting certain cyclodehydrations that cannot be achieved by using classical Lewis acids [84][85]. Additional advantages of PPA

• of PPA esters for the optimization of the heterocyclization reaction leading to compounds 1. Results and Discussion The synthetic strategy leading to DHQs 1 is depicted in Scheme 1. The key step of the sequence involves an N-arylation of 2-ABA with active haloaromatics (Scheme 2). As previously

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

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

Solvent-free copper-catalyzed click chemistry for the synthesis of N-heterocyclic hybrids based on quinoline and 1,2,3-triazole

• Martina Tireli,
• Silvija Maračić,
• Stipe Lukin,
• Marina Juribašić Kulcsár,
• Dijana Žilić,
• Mario Cetina,
• Ivan Halasz,
• Silvana Raić-Malić and
• Krunoslav Užarević

Beilstein J. Org. Chem. 2017, 13, 2352–2363, doi:10.3762/bjoc.13.232

• -aminobiphenyl (1) with ethyl 4,4,4-trifluoro-3-oxobutanoate in polyphosphoric acid (PPA) followed by the cyclization of the Schiff base intermediate afforded the 2-(trifluoromethyl)-6-phenylquinolone 3 (Scheme 1). O-Alkynylquinoline derivative 4 required for the click synthesis of target triazoles was obtained

Syntheses of 3,4- and 1,4-dihydroquinazolines from 2-aminobenzylamine

• Jimena E. Díaz,
• Silvia Ranieri,
• Nadia Gruber and
• Liliana R. Orelli

Beilstein J. Org. Chem. 2017, 13, 1470–1477, doi:10.3762/bjoc.13.145

• reported the MW-assisted synthesis of 1,4,5,6-tetrahydropyrimidines and their homologues by cyclodehydration reactions promoted by polyphosphoric acid (PPA) esters PPE and PPSE [58][59][60]. This strategy was successfully applied to the synthesis of 1-aryl-2-imino-1-azacycloalkanes [61], 2-oxazolines, 5,6

Microwave-assisted cyclizations promoted by polyphosphoric acid esters: a general method for 1-aryl-2-iminoazacycloalkanes

• Jimena E. Díaz,
• María C. Mollo and
• Liliana R. Orelli

Beilstein J. Org. Chem. 2016, 12, 2026–2031, doi:10.3762/bjoc.12.190

• -2-iminoazacycloalkanes is presented, by microwave-assisted ring closure of ω-arylaminonitriles promoted by polyphosphoric acid (PPA) esters. 1-Aryl-2-iminopyrrolidines were easily prepared from the acyclic precursors employing a chloroformic solution of ethyl polyphosphate (PPE). The use of

• trimethylsilyl polyphosphate (PPSE) in solvent-free conditions allowed for the synthesis of 1-aryl-2-iminopiperidines and hitherto unreported 1-aryl-2-iminoazepanes. The cyclization reaction involves good to high yields and short reaction times, and represents a novel application of PPA esters in heterocyclic

• of conventional heating [17]. In previous work, we reported the microwave-assisted synthesis of 5 to 8 membered cyclic amidines by cyclodehydration of N-aryl-N´-acyl-1,n-alkanediamines (n = 2–5) promoted by polyphosphoric acid (PPA) esters PPE and PPSE (Scheme 1, reaction 1) [41][42][43]. In this

Practical synthetic strategies towards lipophilic 6-iodotetrahydroquinolines and -dihydroquinolines

• David R. Chisholm,
• Garr-Layy Zhou,
• Ehmke Pohl,
• Roy Valentine and
• Andrew Whiting

Beilstein J. Org. Chem. 2016, 12, 1851–1862, doi:10.3762/bjoc.12.174

• in Scheme 1, which requires cyclisation from the alkylated N-allylaniline 4. The use of polyphosphoric acid (PPA) in cyclisation reactions is well known in the literature, and has been used to form a large variety of ring structures [15]. Iodination of 3 could then be realised by utilising the rich

• , presumably due to steric hindrance. Cyclisation of 4 to the THQ 3 was realised by heating a PPA mixture of 4 to 120 °C. Iodination of 3 using a variety of reagents including I2/HgO [19], ICl/AcOH, N-iodosuccinimide/TFA [20], KI/KIO3/AcOH [21], and N-chlorosuccinimide/NaI/AcOH [22], all gave poor yields (0–30

• without purification to 10 by heating a DCM solution with a nominal amount of concentrated sulphuric acid. This procedure was much more straightforward when compared to the previous PPA reaction, and required a much less laborious work-up. The increased efficiency of this reaction can be attributed to

Synthesis of a tricyclic lactam via Beckmann rearrangement and ring-rearrangement metathesis as key steps

• Sambasivarao Kotha,
• Ongolu Ravikumar and
• Jadab Majhi

Beilstein J. Org. Chem. 2015, 11, 1503–1508, doi:10.3762/bjoc.11.163

• , reflux, 15 h, CH3CN (c) PPA, reflux for 20 min. Surprisingly, in all these instances no rearrangement product was observed. Interestingly, when the mixture of oximes 8a and 8b was treated with TsCl in the presence of NaOH at rt lactams 9a and 9b were obtained in 66% combined yield for two steps (9a:9b

Selected synthetic strategies to cyclophanes

• Sambasivarao Kotha,
• Mukesh E. Shirbhate and
• Gopalkrushna T. Waghule

Beilstein J. Org. Chem. 2015, 11, 1274–1331, doi:10.3762/bjoc.11.142

An overview of the synthetic routes to the best selling drugs containing 6-membered heterocycles

• Marcus Baumann and
• Ian R. Baxendale

Beilstein J. Org. Chem. 2013, 9, 2265–2319, doi:10.3762/bjoc.9.265

• substituted Grignard reagent 1.26. A Friedel–Crafts type acylation promoted by either triflic acid or polyphosphoric acid (PPA) furnishes the tricyclic structure 1.28 which upon N-demethylation affords clarinex (1.22). One of the top-selling classes of pharmaceuticals containing the pyridine ring are the

An investigation of the observed, but counter-intuitive, stereoselectivity noted during chiral amine synthesis via N-chiral-ketimines

• Thomas C. Nugent,
• Richard Vaughan Williams,
• Andrei Dragan,
• Alejandro Alvarado Méndez and
• Andrei V. Iosub

Beilstein J. Org. Chem. 2013, 9, 2103–2112, doi:10.3762/bjoc.9.247

• an increase in dr as observed here and in all other related research. It is therefore important to note that all solvents used in our study were aprotic. The 1972 report by Harada and co-workers [51] explored the use of (±)-PEA and (±)-phenylpropylamine (PPA) for N-chiral imine formation and noted

• their reduction with Pd-C/H2 in THF. For the PPA imine of phenyl ethyl ketone they stated that different ratios of the cis/trans-imine could be isolated. Unfortunately, they did not describe how to obtain the different cis/trans-imine ratios, other than to state that they change upon sitting after

An efficient access to the synthesis of novel 12-phenylbenzo[6,7]oxepino[3,4-b]quinolin-13(6H)-one derivatives

• Wentao Gao,
• Guihai Lin,
• Yang Li,
• Xiyue Tao,
• Rui Liu and
• Lianjie Sun

Beilstein J. Org. Chem. 2012, 8, 1849–1857, doi:10.3762/bjoc.8.213

• , is described, involving the intramolecular Friedel–Crafts acylation reaction of 2-(phenoxymethyl)-4-phenylquinoline-3-carboxylic acid derivatives 3a–l aided by the treatment with PPA (polyphosphoric acid) or Eaton’s reagent. The required starting compound (2) was obtained by Friedländer reaction of 2

• three-step route, offers easy access to tetracyclic-fused quinoline systems in short reaction times, and the products are obtained in moderate to good yields. Keywords: Eaton’s reagent; Friedel–Crafts acylation; Friedländer reaction; one-pot; PPA; quinoline; tetracyclic-fused; Introduction Polycyclic

• commonly available cyclization agents screened for the intramolecular Friedel–Crafts acylation reaction (e.g., AlCl3, H2SO4, p-TsOH, TiCl4, P2O5), the use of inexpensive and readily available polyphosphoric acid (PPA), requiring no additional solvent, was found to be very suitable for such a reaction in

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

• cyclohexanone, catalyzed by PPA, followed by dehydrogenation over Pd–C has also been reported for the preparation of the unsubstituted α-carboline [48], but no other successful applications of this strategy have appeared in the literature. A more common strategy to α-carbolines closes the pyridine ring onto an

Efficient and improved synthesis of Telmisartan

• A. Sanjeev Kumar,
• Samir Ghosh and
• G. N. Mehta

Beilstein J. Org. Chem. 2010, 6, No. 25, doi:10.3762/bjoc.6.25

• , 0 °C (c) Pd/C, 5 bar, H2, MeOH (d) AcOH, 120 °C, yield: 78% (e) NaOH, MeOH/H2O, 100 °C (f) 2-MeNH-C6H4-NH2, PPA, 150 °C, yield: 64% (g) tBuOK, DMSO, RT (h) TFA, DCM, RT, yield: 42% (i) Cu (5 equiv), 210 °C, (j) HCl, H2O, 100 °C (k) (COCl)2, DCM, 0 °C, (l) tBuOK, THF, RT, yield: 9% (m) NBS, (PhCOO)2

Studies on polynuclear furoquinones. Part 1: Synthesis of tri- and tetra- cyclic furoquinones simulating BCD/ABCD ring system of furoquinone diterpenoids

• Faruk H. Shaik and
• Gandhi K. Kar

Beilstein J. Org. Chem. 2009, 5, No. 47, doi:10.3762/bjoc.5.47

• better result. The next step was the introduction of the phenol functionality. In this case our early attempt to prepare the phenol 12 by PPA cyclization of the acid 9 was unsuccessful. We however successfully prepared the phenol as a light yellow solid by cyclization of the acid 9 with trifluoroacetic

Synthesis of 2-substituted 9-oxa-guanines {5-aminooxazolo[5,4-d]pyrimidin- 7(6H)-ones} and 9-oxa-2-thio- xanthines {5-mercaptooxazolo[5,4-d]pyrimidin- 7(6H)-ones}

• Subrata Mandal,
• Wen Tai Li,
• Yan Bai,
• Jon D. Robertus and
• Sean M. Kerwin

Beilstein J. Org. Chem. 2008, 4, No. 26, doi:10.3762/bjoc.4.26

• -dihydroxypyrimidine (1a) [19] (Figure 2). Unfortunately, for other 5-acylamino analogs of 1a, this route failed to afford the required oxazolo[5,4-d]pyrimidines, presumably due to decomposition of the product at the temperatures required for cyclodehydration. Other cyclodehydration conditions (POCl3, PPA) were also