HPW-Catalyzed environmentally benign approach to imidazo[1,2-a]pyridines

• Luan A. Martinho and
• Carlos Kleber Z. Andrade

Beilstein J. Org. Chem. 2024, 20, 628–637, doi:10.3762/bjoc.20.55

• ·7H2O [36], and ZnCl2 [37], or organic acids such as p-toluenesulfonic acid (PTSA) [38], TFA [39], and AcOH [40], etc. Nonetheless, most of these acids have major drawbacks such as being expensive, dangerous, strong oxidizing, or even potentially explosive, with long reaction times being required. In

Unravelling a trichloroacetic acid-catalyzed cascade access to benzo[f]chromeno[2,3-h]quinoxalinoporphyrins

• Chandra Sekhar Tekuri,
• Pargat Singh and
• Mahendra Nath

Beilstein J. Org. Chem. 2023, 19, 1216–1224, doi:10.3762/bjoc.19.89

• -toluenesulfonic acid (PTSA) as an acidic catalyst in chloroform at 65 °C for three hours, which provided copper(II) benzo[f]chromeno[2,3-h]quinoxalinoporphyrin 3 in 40% yield (Table 1, entry 1). To improve the isolated yield of the desired porphyrin 3, various experiments were performed by reacting copper(II) 2,3

• -diamino-5,10,15,20-tetra(p-tolyl)porphyrin (1) with 2-hydroxynaphthalene-1,4-dione, dimedone and benzaldehyde in the presence of different acidic catalysts such as p-toluenesulfonic acid (PTSA), La(OTf)3, ʟ-ascorbic acid, p-dodecylbenzenesulfonic acid (DBSA), trichloroacetic acid (TCA) and trifluoroacetic

• acid (TFA) in CHCl3 for 3 hours at 65 °C under one-pot operation (Table 1, entries 1–6). Surprisingly, the reaction did not proceed when La(OTf)3 and ʟ-ascorbic acid were used as acidic catalysts (Table 1, entries 2 and 3). In contrast, the use of Brønsted acidic catalysts such as DBSA and PTSA

A two-phase bromination process using tetraalkylammonium hydroxide for the practical synthesis of α-bromolactones from lactones

• Yuki Yamamoto,
• Akihiro Tabuchi,
• Kazumi Hosono,
• Takanori Ochi,
• Kento Yamazaki,
• Shintaro Kodama,
• Akihiro Nomoto and
• Akiya Ogawa

Beilstein J. Org. Chem. 2021, 17, 2906–2914, doi:10.3762/bjoc.17.198

• successfully synthesized carboxylic acid 2a from lactone 1a in good yield, we next investigated the ring-closing reaction of 2a. Various acids and bases (PTSA, hydrochloric acid, NaOH, KOH, and NaHCO3) were used to promote the intramolecular cyclization of 2a; however, no reaction was observed using any of

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

• ] cycloaddition [17] of enone 95 and tert-butyl 2-butynoate (96) with PBu3 and K2CO3/MeOH as additive to give the cycloaddition adduct 97 in 83% yield [43] (Scheme 6C). A seven-step synthesis from 97 gave pentacyclic ketone 98. Pentacyclic ketone 98 was exposed to PTSA under reflux to give the Wagner–Meerwein

Three-component reactions of aromatic amines, 1,3-dicarbonyl compounds, and α-bromoacetaldehyde acetal to access N-(hetero)aryl-4,5-unsubstituted pyrroles

• Wenbo Huang,
• Kaimei Wang,
• Ping Liu,
• Minghao Li,
• Shaoyong Ke and
• Yanlong Gu

Beilstein J. Org. Chem. 2020, 16, 2920–2928, doi:10.3762/bjoc.16.241

• obtained with AlCl3 (Table 1, entries 4 and 5). p-Toluenesulfonic acid (PTSA), a strong Brønsted acid, also exhibited a promising catalytic ability, and the yield of 4a reached 73% (Table 1, entry 6). When HOAc was used, only unreacted starting materials were recovered (Table, entry 7). The effect of the

Selective preparation of tetrasubstituted fluoroalkenes by fluorine-directed oxetane ring-opening reactions

• Clément Q. Fontenelle,
• Thibault Thierry,
• Romain Laporte,
• Emmanuel Pfund and
• Thierry Lequeux

Beilstein J. Org. Chem. 2020, 16, 1936–1946, doi:10.3762/bjoc.16.160

• bromomethyllactone 15 was observed (Table 4, entry 4). It appeared obvious that Z-13 could cyclize under acidic conditions and during the purification gave β-bromomethyllactone 15. This was later confirmed when various ester/lactone mixtures obtained after the ring-opening reaction were treated with acid (PTSA) in

Application of chiral 2-isoxazoline for the synthesis of syn-1,3-diol analogs

• Juanjuan Feng,
• Tianyu Li,
• Jiaxin Zhang and
• Peng Jiao

Beilstein J. Org. Chem. 2019, 15, 1840–1847, doi:10.3762/bjoc.15.179

• the amount of the chiral Lewis acid catalyst led to a decrease of both the ee and the yield. Desilylation of the 2-isoxazolidine 1 was effected in CHCl3 using catalytic amounts of p-toluenesulfonic acid (PTSA). Though the yield of the in situ-generated 2-isoxazoline 2 bearing the 1,3-oxazolidin-2-one

• crude reaction mixture containing 2 and PTSA was concentrated before excess Et3N was added followed by CH3OH as the solvent. These operations removed the 1,3-oxazolidin-2-one auxiliary while preserving the THP group, and afforded the corresponding methyl ester 3 (Table 1), which was stable and could be

• easily removed the ethylborane group. Removal of THP in 9 delivered a 1,3,5-trihydroxy compound 10. In another way, 10 could be prepared by treating 8 with PTSA in CH3OH at rt. NMR spectra of 8–10 exhibited only one set of signals corresponding to the syn-dihydroxy products, indicating an extra high

Functional panchromatic BODIPY dyes with near-infrared absorption: design, synthesis, characterization and use in dye-sensitized solar cells

• Quentin Huaulmé,
• Cyril Aumaitre,
• Outi Vilhelmiina Kontkanen,
• David Beljonne,
• Alexandra Sutter,
• Gilles Ulrich,
• Renaud Demadrille and
• Nicolas Leclerc

Beilstein J. Org. Chem. 2019, 15, 1758–1768, doi:10.3762/bjoc.15.169

• dyes. Synthetic scheme of the selected materials. a) hydroxylamine hydrochloride, NaHCO3, DMSO, 60 °C then acetylene, KOH, DMSO, 110 °C, 24% over the two steps; b) 4-iodobenzoyl chloride, DCM, rt then DDQ, DCM, rt then NEt3, BF3·OEt2, 0 °C to rt, 35%; c) piperidine, cat. PTSA, toluene, 130 °C, 5: 35

N-(1-Phenylethyl)aziridine-2-carboxylate esters in the synthesis of biologically relevant compounds

• Iwona E. Głowacka,
• Aleksandra Trocha,
• Andrzej E. Wróblewski and
• Dorota G. Piotrowska

Beilstein J. Org. Chem. 2019, 15, 1722–1757, doi:10.3762/bjoc.15.168

Alkylation of lithiated dimethyl tartrate acetonide with unactivated alkyl halides and application to an asymmetric synthesis of the 2,8-dioxabicyclo[3.2.1]octane core of squalestatins/zaragozic acids

• Herman O. Sintim,
• Hamad H. Al Mamari,
• Hasanain A. A. Almohseni,
• Younes Fegheh-Hassanpour and
• David M. Hodgson

Beilstein J. Org. Chem. 2019, 15, 1194–1202, doi:10.3762/bjoc.15.116

• THF both decomposed 19a into unidentifiable polar products. Attempted acid-induced loss of acetone with PTSA in MeOH, PPTS in refluxing MeOH, or 80% AcOH at reflux [27] all led to quantitative recovery of hydroxy acetonide 19a, whereas 5% aq HCl resulted in acetonide removal and concomitant

Synthesis of nonracemic hydroxyglutamic acids

• Dorota G. Piotrowska,
• Iwona E. Głowacka,
• Andrzej E. Wróblewski and
• Liwia Lubowiecka

Beilstein J. Org. Chem. 2019, 15, 236–255, doi:10.3762/bjoc.15.22

• ) NaIO4, RuO2, H2O; c) NaOH, H2O then HCl, H2O; d) CH2N2, ether; e) Me3SiNEt2; f) MeOH, PTSA; g) KMnO4, NaOH, H2O; h) HCl, H2O. Synthesis of (2S,3R)-2 and (2S,3S)-2 from (R)-Garner’s aldehyde. Reagents and conditions: a) H2C=CHCH2MgCl, ZnCl2, THF; b) BnBr, NaH, THF; c) 4-methylmorpholine N-oxide, OsO4

• , H2O; b) BuLi, THF; then H2C=CHCH2MgBr; c) L-selectride, THF; d) Me2C(OMe)2, PTSA, THF; e) O3, CH2Cl2, ether, then Ph3P; f) KMnO4, acetone, H2O; g) t-BuOH, N,N′-diisopropyl-O-tert-butylisourea, CH2Cl2; h) MeOH, HCl (gas); i) O2, Pt, AcOEt, H2O; j) electrochemical reduction. Synthesis of (2R,3S)-2 from

• sequence. Reagents and conditions: a) (CF3CH2O)2P(O)CH2COOMe, KHMDS, 18-crown-6, THF; b) PTSA, MeOH; c) NaOCl, TEMPO, KBr, NaHCO3, water/acetone; d) 3 M HCl, 80 °C. Synthesis of the orthogonally protected (2S,3R)-2 from a chiral aziridine. Reagents and conditions: a) LiHMDS, AcOt-Bu, THF; b) NaBH4, iPrOH

Synthesis of a leopolic acid-inspired tetramic acid with antimicrobial activity against multidrug-resistant bacteria

• Luce Mattio,
• Loana Musso,
• Leonardo Scaglioni,
• Andrea Pinto,
• Piera Anna Martino and
• Sabrina Dallavalle

Beilstein J. Org. Chem. 2018, 14, 2482–2487, doi:10.3762/bjoc.14.224

• , afforded the desired O-alkyltetramic acid 13 in 30% yield. The synthesis of the activated ureido fragment was achieved in four steps from suitably protected L-valine and L-phenylalanine. The benzyl protection of L-phenylalanine (14) was carried out with PTSA and benzyl alcohol in toluene and the ester 15

Synthesis of 1,4-imino-L-lyxitols modified at C-5 and their evaluation as inhibitors of GH38 α-mannosidases

• Maroš Bella,
• Sergej Šesták,
• Ján Moncoľ,
• Miroslav Koóš and
• Monika Poláková

Beilstein J. Org. Chem. 2018, 14, 2156–2162, doi:10.3762/bjoc.14.189

• achieved by N-debenzylation under catalytic hydrogenolysis conditions followed by protection of the liberated amines with CbzCl furnishing fully protected pyrrolidines 14 [35] and 15. Exposure of 14 to a catalytic amount of PTSA (0.04 equiv) in a mixture of CH2Cl2/MeOH 30:1 (v/v) resulted in rapid cleavage

Synthetic avenues towards a tetrasaccharide related to Streptococcus pneumonia of serotype 6A

• Aritra Chaudhury,
• Mana Mohan Mukherjee and
• Rina Ghosh

Beilstein J. Org. Chem. 2018, 14, 1095–1102, doi:10.3762/bjoc.14.95

• deprotection of the naphthylmethyl group gave the acceptor 5 [27] in 83% yield (Scheme 2). For acceptor 7 (Figure 2) ribitol 17 was converted to its corresponding diisopropylidene derivative 18 [37] in the presence of dimethoxypropane and pTSA in acetone. Treatment with NapBr and NaH in DMF gave compound 19 in

• 93% yield. Subsequent deprotection of isopropylidene ketal with pTSA/MeOH (aq) and then benzylation furnished 20 in 95% yield over two steps. Deprotection of the naphthylmethyl group in the presence of DDQ in aqueous dichloromethane (19:1) gave the glycosyl acceptor 7 [22] in 85% yield (Scheme 3). In

• (OMe)2, pTSA, CH3COCH3, rt, 81%; b) NapBr, NaH, DMF, rt, 8 h, 93%; c) (i) pTSA, MeOH, 40 °C, 4 h, (ii) BnBr, NaH, DMF, rt, 12 h, 95% over 2 steps; d) DDQ, DCM/H2O (19:1), rt, 2 h, 85%. Stepwise synthesis of tetrasaccharide 1. Reaction conditions: a) TMSOTf, DCM/Et2O (5:1), 4 Å MS, −30 °C, 75%; b) DDQ

Mannich base-connected syntheses mediated by ortho-quinone methides

• Petra Barta,
• Ferenc Fülöp and
• István Szatmári

Beilstein J. Org. Chem. 2018, 14, 560–575, doi:10.3762/bjoc.14.43

• -hydroxypropanals and cyclic secondary amines, Jha et al. achieved the synthesis of 2,2-dialkyl-3-dialkylamino-2,3-dihydro-1H-naphtho[2,1-b]pyrans under solvent-free conditions using pTSA as catalyst [75]. It is important to note, that during the reaction, 2,2-disubstituted 3-hydroxypropanals 26 decompose to

Palladium-catalyzed ortho-halogenations of acetanilides with N-halosuccinimides via direct sp² C–H bond activation in ball mills

• Zi Liu,
• Hui Xu and
• Guan-Wu Wang

Beilstein J. Org. Chem. 2018, 14, 430–435, doi:10.3762/bjoc.14.31

• because the addition of acids into the reaction system could promote the C–H bond halogenation according to the previous literature [46]. As desired, compound 2a was isolated in 87% yield when p-toluenesulfonic acid (PTSA) was employed (Table 1, entry 2). A control experiment was conducted for the

• reaction of 1a with NIS in the absence of Pd(OAc)2, yet still with PTSA as the promoter, and no iodinated product was furnished (Table 1, entry 3). The use of D-camphorsulfonic acid (D-CSA) or mesitylenesulfonic acid dihydrate provided inferior results than that obtained in the presence of PTSA (Table 1

• , entries 4 and 5 vs entry 2). Furthermore, no desired product was obtained when pyridine-2-sulfonic acid, 2-nitrobenzoic acid, 2-aminoethanesulfonic acid or tungstophosphoric acid hydrate (HPA) was used in the reaction (Table 1, entries 6–9). Thus, the combination of Pd(OAc)2 with PTSA was essential for

Mechanochemical synthesis of small organic molecules

• Tapas Kumar Achar,
• Anima Bose and
• Prasenjit Mal

Beilstein J. Org. Chem. 2017, 13, 1907–1931, doi:10.3762/bjoc.13.186

• reaction medium, solvent-free synthesis, microwave synthesis, use of different Lewis acids FeCl3, NiCl2, BiCl3, InBr3, use of Brønsted acids PTSA, etc. are also reported [129][130]. Recently, Mal and co-workers reported a mechanochemical Biginelli reaction by a subcomponent synthesis approach [131][132

The chemistry and biology of mycolactones

• Matthias Gehringer and
• Karl-Heinz Altmann

Beilstein J. Org. Chem. 2017, 13, 1596–1660, doi:10.3762/bjoc.13.159

A practical and efficient approach to imidazo[1,2-a]pyridine-fused isoquinolines through the post-GBB transformation strategy

• Taofeng Shao,
• Zhiming Gong,
• Tianyi Su,
• Wei Hao and
• Chao Che

Beilstein J. Org. Chem. 2017, 13, 817–824, doi:10.3762/bjoc.13.82

• investigating the GBB reaction of 2-aminopyridine (1a), 2-ethynylbenzaldehyde (2a) and tert-butylisocyanide (3). The GBB reaction proceeded smoothly in MeOH in the presence of catalytic PTSA or HClO4 at room temperature to afford imidazo[1,2-a]pyridine 4a in 90% yield, and the cyclized product 6a was not

N-Propargylamines: versatile building blocks in the construction of thiazole cores

• S. Arshadi,
• E. Vessally,
• L. Edjlali,
• R. Hosseinzadeh-Khanmiri and
• E. Ghorbani-Kalhor

Beilstein J. Org. Chem. 2017, 13, 625–638, doi:10.3762/bjoc.13.61

• of p-toluenesulfonic acid (PTSA) as catalyst under microwave irradiation was developed by Castagnolo et al. Following this route, several 4-substituted 5-methylthiazol-2-amines 22 were synthesized from terminal N-propargylamines 20 and isothiocyanates 21 in DMF at 160 °C. Interestingly, when internal

The synthesis of α-aryl-α-aminophosphonates and α-aryl-α-aminophosphine oxides by the microwave-assisted Pudovik reaction

• Erika Bálint,
• Ádám Tajti,
• Anna Ádám,
• István Csontos,
• Konstantin Karaghiosoff,
• Mátyás Czugler,
• Péter Ábrányi-Balogh and
• György Keglevich

Beilstein J. Org. Chem. 2017, 13, 76–86, doi:10.3762/bjoc.13.10

• ][34][35][36][37][38], while in a few cases the catalysts, i.e., PTSA [39], Na [40], TEA [21] or MoO2Cl2 [41], were used under solvent-free conditions. As for the microwave (MW)-assisted additions, only two cases were reported, but the catalytic variations were carried out in kitchen MW ovens [32][42

The in situ generation and reactive quench of diazonium compounds in the synthesis of azo compounds in microreactors

• Faith M. Akwi and
• Paul Watts

Beilstein J. Org. Chem. 2016, 12, 1987–2004, doi:10.3762/bjoc.12.186

• temperature: Azo coupling reaction. PTSA-catalyzed diazotization and azo coupling reaction. Ferric hydrogen sulfate (FHS) catalyzed azo compound synthesis. Synthesis of azo compounds in the presence of silica supported boron trifluoride. Phase transfer catalyzed azo coupling of 5-methylresorcinol in

One-pot synthesis of tetracyclic fused imidazo[1,2-a]pyridines via a three-component reaction

• Bo Yang,
• Chuanye Tao,
• Taofeng Shao,
• Jianxian Gong and
• Chao Che

Beilstein J. Org. Chem. 2016, 12, 1487–1492, doi:10.3762/bjoc.12.145

• precipitation from the reaction mixture and n-BuOH proved to be the most suitable solvent in the reaction. Performing the reaction in refluxing n-BuOH in the presence of one equivalent of HClO4 for 8 h, compound 1a was obtained in 30% isolated yield. Other acids including p-toluenesulfonic acid (PTSA), HCl, and

• HOAc were also screened, and the results indicated that the use of PTSA led to a slightly decreased yield, and weaker acids failed to promote this process. It is worth noting that the reaction proceeded incompletely and significant amounts of isatin (3a) were recovered. When increased amounts (1.35

Efficient syntheses of climate relevant isoprene nitrates and (1R,5S)-(−)-myrtenol nitrate

• Sean P. Bew,
• Glyn D. Hiatt-Gipson,
• Graham P. Mills and
• Claire E. Reeves

Beilstein J. Org. Chem. 2016, 12, 1081–1095, doi:10.3762/bjoc.12.103

• ) was straightforward. Heating rac-74 with a mixture of acetic anhydride and para-toluenesulfonic acid (PTSA, 1 equiv) afforded via, presumably, protonated rac-75 ring-opened and O-acylated (±)-1-bromo-3-methylbut-3-en-2-yl acetate (rac-76) in a 58% yield. Isolation, solvent removal and purification of

Towards inhibitors of glycosyltransferases: A novel approach to the synthesis of 3-acetamido-3-deoxy-D-psicofuranose derivatives

• Maroš Bella,
• Miroslav Koóš and
• Chun-Hung Lin

Beilstein J. Org. Chem. 2015, 11, 1547–1552, doi:10.3762/bjoc.11.170

• ) H2SO4, 70% AcOH, 0 °C → rt, 4 h, 84%; c) 2,2-dimethoxypropane, acetone, PTSA, rt, 4 h, 63%; d) Ac2O, pyridine, CH2Cl2, rt, overnight, 92%; e) MeONa, MeOH, rt, overnight, 97%. Reagents and conditions: a) EtSH, BF3·OEt2, CH2Cl2, −5 °C → rt, 4 h, 13: 55%, 14: 34%. Crystallographic and experimental dataa