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

• potentially useful molecules. Keywords: Cannizzaro reaction; crossed-Cannizzaro; desymmetrization; Lewis acid catalyst; natural products; Introduction The synthesis of functionalized molecules with structural complexity has always been a challenge to synthetic chemists. The Cannizzaro reaction, in its

• in subsequent reactions. Reddy and coworkers carried out the Cannizzaro reaction of aromatic aldehydes to the corresponding alcohols in high yields by crossed-Cannizzaro reactions employing solid-supported KF-Al2O3 as catalyst [26] under microwave irradiation using solvent-free conditions. The use of

• -transfer catalyst in the presence of KOH as the base. Canipelle et al. [28] put forward an improved Cannizzaro disproportionation of 4-biphenylcarboxaldehyde into the corresponding alcohol and carboxylic acid products employing cyclodextrins as the phase-transfer agent. A Cannizzaro desymmetrization

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

• , such as iridium complexes or organic dyes, and activating agents, including dimethyl dicarbonate (DMDC) and PPh3. Redox-active esters are created when activating agents and carboxylic acids react. These esters can then be reduced using a photoredox catalyst to produce the acyl radical. In 2019, Doyle

• catalyst is first excited and then transfers one electron to the thiocarbamate moiety to form a thiocarbamate radical anion, with change in oxidation state from III to IV. Next, the sacrificial electron donor Hünig base successfully converts [Ir(IV)] to [Ir(III)], with concurrent formation of an amine

• )], 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

Rhodium-catalyzed homo-coupling reaction of aryl Grignard reagents and its application for the synthesis of an integrin inhibitor

• Kazuyuki Sato,
• Satoki Teranishi,
• Atsushi Sakaue,
• Yukiko Karuo,
• Atsushi Tarui,
• Kentaro Kawai,
• Hiroyuki Takeda,
• Tatsuo Kinashi and
• Masaaki Omote

Beilstein J. Org. Chem. 2024, 20, 1341–1347, doi:10.3762/bjoc.20.118

• for integrins which is critical for several diseases. Keywords: biphenyltetracarboxylic acid; homo-coupling; integrin inhibitor; rhodium catalyst; Ullmann-type reaction; Introduction The Ullmann reaction is a coupling reaction of aryl halides using copper, traditionally using metallic copper-bronze

• reaction mixture (Table 1, entry 10). Next, we investigated various Rh catalysts and solvents, and the results are summarized in Table 2. All Rh catalysts that were examined in this reaction gave the product in good yields, although in the absence of a Rh catalyst the reaction failed as shown in Table 2

• , entries 1–8. In addition, there was no need to prolong the reaction time (entry 3 in Table 2). Therefore, a Rh catalyst is essential in this reaction, and RhCl(PPh3)3 was chosen as the best catalyst because of its availability. In the examination of the reaction solvents, the use of THF led to the highest

Transition-metal-catalyst-free electroreductive alkene hydroarylation with aryl halides under visible-light irradiation

• Kosuke Yamamoto,
• Kazuhisa Arita,
• Masami Kuriyama and
• Osamu Onomura

Beilstein J. Org. Chem. 2024, 20, 1327–1333, doi:10.3762/bjoc.20.116

• high regioselectivity. Herein, we report the electroreductive hydroarylation of electron-deficient alkenes and styrene derivatives using (hetero)aryl halides under mild reaction conditions. Notably, the present hydroarylation proceeded with high efficiency under transition-metal-catalyst-free

• by preventing overreduction [39]. While the metal-catalyst-free radical cyclization of alkene-tethered aryl halides has been well documented in the literature [40][41][42][43], the efficient intermolecular hydroarylation of alkenes still relies on the use of transition-metal catalysts, including Pd

• [44], Ni [45], and Co [46] (Scheme 1a). The pioneering work by Savéant et al. demonstrated that electron-deficient (hetero)aromatics acted as efficient mediators for the metal-catalyst-free electroreductive hydroarylation of alkenes with some activated chloro-, bromo-, and iodoarenes, but the use of a

Phenotellurazine redox catalysts: elements of design for radical cross-dehydrogenative coupling reactions

• Alina Paffen,
• Christopher Cremer and
• Frederic W. Patureau

Beilstein J. Org. Chem. 2024, 20, 1292–1297, doi:10.3762/bjoc.20.112

• enabling the activation of small yet highly relevant organic substrates. For example, Huber and co-authors recently designed a Te-based catalyst in an indole Michael addition reaction [1][2][3][4][5]. Pale and Mamane utilized another Te-based catalyst in an electrophilic bromine-mediated cyclization

• simple oxygen atmosphere (Scheme 1a) [30][31][32]. Most recently, we also showed that phenotellurazines could catalyze the oxidative dimerization of indoles, likewise under a simple oxygen atmosphere. 2-Methoxyphenotellurazine PTeZ2 proved to be the optimal catalyst in the latter case (Scheme 1b) [33

• ]. In the present study, we decided to revisit the design of the phenotellurazine redox catalyst, in the hope of improving it as well as enabling new catalytic reactivity. In particular, we wished to investigate and optimize the level of electronic cooperativity between the Te- and N-centers, the effect

Oxidative hydrolysis of aliphatic bromoalkenes: scope study and reactivity insights

• Amol P. Jadhav and
• Claude Y. Legault

Beilstein J. Org. Chem. 2024, 20, 1286–1291, doi:10.3762/bjoc.20.111

• by stoichiometric use of HTIB. Attempt to perform the reaction using a catalytic amount of 2-iodobenzoic acid (0.2) under similar oxidizing conditions resulted in slightly diminished yield for the desired α-bromoketone (Table 2, entry 2). Notably, the direct use of HTIB as the catalyst, with a

• the iodonium intermediate C. Liberation of PhI serves as the driving force for subsequent SN2 attack by the bromide anion to give the dialkyl α-bromoketone 2. m-CPBA then regenerates the hypervalent iodine (HTIB) catalyst by oxidizing PhI in the presence of TsOH·H2O. The formation of the Ritter-type

Synthesis and optical properties of bis- and tris-alkynyl-2-trifluoromethylquinolines

• Stefan Jopp,
• Franziska Spruner von Mertz,
• Peter Ehlers,
• Alexander Villinger and
• Peter Langer

Beilstein J. Org. Chem. 2024, 20, 1246–1255, doi:10.3762/bjoc.20.107

• bromide gave 4. With quinoline 4 in hand, we studied palladium-catalysed Sonogashira reactions with phenylacetylene (5a). Gratifyingly, our initial test reaction, using Pd(OAc)2 as catalyst with XPhos as ligand, gave bis-alkynylated product 6a in quantitative yield. Reducing the catalyst loading from 5 to

• 2.5 mol % or switching to more simple Pd(PPh3)4 still achieved quantitative yields. Less catalyst led to a reduced yield (Table 1). Consequently, we chose 2.5 mol % Pd(PPh3)4 for all further reactions. As a next step, we analysed the scope of our methodology (Scheme 2). The optimized conditions allow

Mechanistic investigations of polyaza[7]helicene in photoredox and energy transfer catalysis

• Johannes Rocker,
• Till J. B. Zähringer,
• Matthias Schmitz,
• Till Opatz and
• Christoph Kerzig

Beilstein J. Org. Chem. 2024, 20, 1236–1245, doi:10.3762/bjoc.20.106

• thorough photochemical characterization is essential for efficient light-driven applications. In this article, the mode of action of a polyazahelicene catalyst (Aza-H) was investigated using laser flash photolysis (LFP). The study revealed that the chromophore can function as a singlet-state photoredox

• catalyst in the sulfonylation/arylation of styrenes and as a triplet sensitizer in energy transfer catalysis. The singlet lifetime is sufficiently long to exploit the exceptional excited state reduction potential for the activation of 4-cyanopyridine. Photoinduced electron transfer generating the radical

• with a quantum yield of 0.34. The pronounced triplet formation was exploited for the isomerization reaction of (E)-stilbene to the Z-isomer and the cyclization of cinnamyl chloride. Catalyst degradation mainly occurs through the long-lived Aza-H triplet (28 µs), but the photostability is greatly

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

• mechanism for the formation of oxamide is shown in Scheme 6. Formation of acetanilide in the reaction of aniline and acetonitrile is known to occur in the presence of Lewis acid catalyst Al2O3 [55]. In our case, either SeO2 (Lewis acid) or H2SeO3 (Brønsted acid) may act as acid catalyst to convert aniline

The Ugi4CR as effective tool to access promising anticancer isatin-based α-acetamide carboxamide oxindole hybrids

• Carolina S. Marques,
• Aday González-Bakker and
• José M. Padrón

Beilstein J. Org. Chem. 2024, 20, 1213–1220, doi:10.3762/bjoc.20.104

• using 5-amino-1-benzyl-3,3-dimethoxyindolin-2-one (1) [12] and benzyl isocyanide (4), as amine and isocyanide components, respectively. Different carboxylic acids 2 and aldehydes/ketones 3 were evaluated using ZnF2 as catalyst (10 mol %) and MeOH as the solvent (Scheme 2 and Figure 2). A library of α

• into the scaffold. Benzyl azide (6), obtained using a previously reported procedure [27], was used in the CuAAC reaction. The α-acetamide carboxamide 1,2,3-triazole oxindole hybrid 7 was easily obtained in 61% yield using Cu(OAc)2 as catalyst, ascorbic acid, DMF as solvent, and microwave reaction

Introduction of peripheral nitrogen atoms to cyclo-meta-phenylenes

• Koki Ikemoto and
• Hiroyuki Isobe

Beilstein J. Org. Chem. 2024, 20, 1207–1212, doi:10.3762/bjoc.20.103

• -doped [n]CMPs, 3a and 3b, were synthesized via one-pot Suzuki–Miyaura coupling [12] (Scheme 1). Previously, we synthesized [n]CMPs with inward-focused nitrogen dopants by using Suzuki–Miyaura coupling with Pd(PPh3)4 as the catalyst [13] and applied this method to outward-radiated congeners in this work

Bismuth(III) triflate: an economical and environmentally friendly catalyst for the Nazarov reaction

• Manoel T. Rodrigues Jr.,
• Aline S. B. de Oliveira,
• Ralph C. Gomes,
• Amanda Soares Hirata,
• Lucas A. Zeoly,
• Hugo Santos,
• João Arantes,
• Catarina Sofia Mateus Reis-Silva,
• João Agostinho Machado-Neto,
• Leticia Veras Costa-Lotufo and
• Fernando Coelho

Beilstein J. Org. Chem. 2024, 20, 1167–1178, doi:10.3762/bjoc.20.99

• , 13083-970 Campinas, São Paulo, Brazil Department of Pharmacology, Institute of Biomedical Sciences, University of São Paulo, 05508-000 São Paulo, Brazil 10.3762/bjoc.20.99 Abstract We describe the use of bismuth(III) triflate as an efficient and environmentally friendly catalyst for the Nazarov

• the Nazarov reaction, using models already studied in the literature [33][34][35][36][37][38][39][40][41][42][43]. We investigated several conditions, such as the type of catalyst, temperature, solvent, and amount of catalyst (Table 1). Our optimization studies began with the reaction of substrate 9aa

• ). Once the catalyst was chosen, we investigated the influence of the solvent. For this purpose, we evaluated dichloroethane (DCE), dichloromethane (DCM), toluene, and tetrahydrofuran (THF) as solvents for the transformation (Table 1, entries 16–19), but acetonitrile remained the best solvent. Finally, we

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

• compounds. To achieve the selective C–C and C–N bond formation via hydrogen borrowing, controlling the selectivity is an important factor since the formation of possible side-products such as overreduction of unsaturated compounds or dialkylation. Hence, developing an efficient catalyst, capable of

• -methylation of amines with methanol was achieved with lower catalyst and base loading. Sortais et al. reported an elegant example of a manganese-catalyzed N-methylation of primary amines with methanol using catalytic amounts of base. They synthesized a novel Mn(I) complex bearing a bis(diaminopyridine

• synthesis of amines and imines using Mn-pincer catalyst [37]. When t-BuOK (1 equiv) was used as a base, alkylated amine products were observed selectively using alcohol as an alkylating agent, whereas when t-BuONa (1.5 equiv) was used as base, alkylated imine products were isolated (Scheme 6). This

Synthesis of 1,4-azaphosphinine nucleosides and evaluation as inhibitors of human cytidine deaminase and APOBEC3A

• Maksim V. Kvach,
• Stefan Harjes,
• Harikrishnan M. Kurup,
• Geoffrey B. Jameson,
• Elena Harjes and
• Vyacheslav V. Filichev

Beilstein J. Org. Chem. 2024, 20, 1088–1098, doi:10.3762/bjoc.20.96

• double bond in the nucleobase, providing nucleoside 24 (Scheme 3). To circumvent this problem, we used poisoned Pd catalyst (Lindlar’s catalyst, 5% Pd/CaCO3/3% Pb) and obtained the desired nucleoside 18. Individual anomers of nucleosides 18 and 24 were separated on a C18 column using a gradient of CH3CN

Novel route to enhance the thermo-optical performance of bicyclic diene photoswitches for solar thermal batteries

• Akanksha Ashok Sangolkar,
• Rama Krishna Kadiyam and
• Ravinder Pawar

Beilstein J. Org. Chem. 2024, 20, 1053–1068, doi:10.3762/bjoc.20.93

• transformation into a high energy photoisomer [8][9][10][11][12][13]. This photoisomer then can be stored for a certain period and thermal energy can be released when triggered with heat, light, catalyst, etc. The back isomerization of the metastable photoproduct regenerates the parent molecule for continuing

Carbonylative synthesis and functionalization of indoles

• Alex De Salvo,
• Raffaella Mancuso and
• Xiao-Feng Wu

Beilstein J. Org. Chem. 2024, 20, 973–1000, doi:10.3762/bjoc.20.87

• recent achievements on the synthesis and functionalization of indole derivatives via carbonylative approaches. Keywords: carbonylation; functionalization; indole; metal catalyst; organometallic chemistry; Introduction Indole is a heterocyclic compound consisting of a benzene ring fused with a pyrrole

• 1883 and involves its synthesis from phenylhydrazine and an aldehyde or ketone using an appropriate acid catalyst [8]. In the following years, new processes were developed for the synthesis of indole such as the Castro, Bischler, and Larock synthesis etc. [2][9][10]. Carbonylation reactions represent a

• carbon monoxide insertion, and Suzuki–Miyaura coupling reaction, from 2-gem-dibromovinylaniline [12]. In the presence of Pd(PPh3)4 (5 mol %) as catalyst, 5 equivalents of base (K2CO3), an aryl- or heteroarylboronic ester (1.1 equivalents), CO (12 bar), in dioxane at 100 °C after 16 h the indole

Enantioselective synthesis of β-aryl-γ-lactam derivatives via Heck–Matsuda desymmetrization of N-protected 2,5-dihydro-1H-pyrroles

• Arnaldo G. de Oliveira Jr.,
• Martí F. Wang,
• Rafaela C. Carmona,
• Danilo M. Lustosa,
• Sergei A. Gorbatov and
• Carlos R. D. Correia

Beilstein J. Org. Chem. 2024, 20, 940–949, doi:10.3762/bjoc.20.84

• all other lactams as R was done by analogy. The assignment of the absolute stereochemistry allowed us to propose a rationale for the Heck–Matsuda reaction (Scheme 7). Upon activation of the catalyst (I), oxidative addition of aryldiazonium salt and subsequent nitrogen release generates the cationic

Synthesis and properties of 6-alkynyl-5-aryluracils

• Ruben Manuel Figueira de Abreu,
• Till Brockmann,
• Alexander Villinger,
• Peter Ehlers and
• Peter Langer

Beilstein J. Org. Chem. 2024, 20, 898–911, doi:10.3762/bjoc.20.80

• -coupling was carried out using Pd(PPh3)4 as catalyst with K3PO4 as base in toluene as solvent which gave a mixture of different products. Further investigation revealed the presence of the two-fold Sonogashira–Hagihara product, starting material 2, and the desired product 3. Hence, starting material 2 and

• be activated, and the 5-position deactivated for the nucleophilic attack that occurs during the oxidative addition of the metal catalyst. This may explain the formation of only the 6-substituted product during the Sonogashira reaction. As mentioned above, new reaction conditions had to be chosen to

• synthesize the desired product 4 and to avoid a mixture. A different catalyst and a higher temperature were chosen to obtain the desired products in higher yields. With the optimized conditions in hand (Pd(CH3CN)2Cl2 (5 mol %), CuI (5 mol %), NEt3 (10 equiv), dioxane, 100 °C, 6 h), the scope was investigated

Ortho-ester-substituted diaryliodonium salts enabled regioselective arylocyclization of naphthols toward 3,4-benzocoumarins

• Ke Jiang,
• Cheng Pan,
• Limin Wang,
• Hao-Yang Wang and
• Jianwei Han

Beilstein J. Org. Chem. 2024, 20, 841–851, doi:10.3762/bjoc.20.76

• , herein, we utilized a copper catalyst to activate the C–I bond of diaryliodonium salts in the generation of aryl radicals, thus resulting in an annulation reaction with naphthols and substituted phenols. This approach yielded a diverse array of 3,4-benzocoumarin derivatives bearing various substituents

• diaryliodonium salt 2a. Naphthol 1a forms intermediate B with A after participation with the Cu(II) catalyst. Intermediate B generates C by radical substitution. A final intramolecular transesterification yields the benzocoumarin product 3aa. Conclusion In summary, we have employed ortho-ester-substituted

Advancements in hydrochlorination of alkenes

• Daniel S. Müller

Beilstein J. Org. Chem. 2024, 20, 787–814, doi:10.3762/bjoc.20.72

• leading to anti-Markovnikov products via several pathways. We have chosen not to present a fourth class of reactions involving either HCl gas or CuCl2 and a Pd catalyst, as reported by Alper [20] and Sigman [21], as these reactions are somewhat exotic and are sufficiently discussed in Yang’s review [14

• solution of HCl, even in the presence of secondary alcohol and ester functionalities (Scheme 5B) [45]. An application in the synthesis of Δ9-tetrahydrocannabutol, the butyl homologue of Δ9-tetrahydrocannabinol (Δ9-THC), is outlined in Scheme 5C [46]. In this case, ZnCl2 was employed as a catalyst, but

• unfortunately data in the absence of ZnCl2 was not provided by the authors. ZnCl2 has been previously reported as a catalyst for hydrochlorination reactions, notably in the case of cyclooctene (25) with HCl in benzene (Scheme 5D) [47]. The use of ZnCl2 as a catalyst for hydrochlorinations dates back to a patent

SOMOphilic alkyne vs radical-polar crossover approaches: The full story of the azido-alkynylation of alkenes

• Julien Borrel and
• Jerome Waser

Beilstein J. Org. Chem. 2024, 20, 701–713, doi:10.3762/bjoc.20.64

• ]. Moreover, different azide sources are known to efficiently promote the diazidation of alkenes in the presence of a copper catalyst, often proceeding via a radical mechanism [24][29][30][31]. A second approach would involve SOMOphilic alkynes to trap the radical by a purely open-shell mechanism (Scheme 1B

• since it is known to be reduced by photocatalysts such as Cu(dap)2Cl [17]. This perfectly fits a catalytic cycle involving the reduction of Ts-ABZ (3) followed by oxidation of the carbon radical to form a carbocation and regenerate the ground state catalyst. Styrene (1a) was used as model substrate

• a non-complexed copper catalyst formed during the transformation [24][51]. When iridium-based photocatalysts were tested, no product formation or only traces were observed (Table 2, entries 2 and 3). Using Ru(bpy)3Cl2·6H2O afforded 17% of 4a, a similar yield as with Cu(dap)2Cl with a reduced

Evaluation of the enantioselectivity of new chiral ligands based on imidazolidin-4-one derivatives

• Jan Bartáček,
• Karel Chlumský,
• Jan Mrkvička,
• Lucie Paloušová,
• Miloš Sedlák and
• Pavel Drabina

Beilstein J. Org. Chem. 2024, 20, 684–691, doi:10.3762/bjoc.20.62

• chiral metal complex catalyst but also as an enantioselective organocatalyst [17]. Accordingly, its application in enantioselective organocatalysis, particularly in asymmetric reactions through “enamine activation”, warrants further investigation. Results and Discussion The corresponding copper(II

• (i.e., temperature, reaction time, amount of catalyst, solvent) were adopted from the pilot study [5] for relevant comparison of catalyst characteristics. From Table 1 and Table 2, which summarise results obtained using tridentate ligands Ia–c and IIa–c, it is evident that the catalytic activity their

• , the other afforded the nitroaldols with ee values of 60–90%. Finally, the complexes of ligands with cis-cis configuration (Ic and IIc) were evaluated. These catalyst are the most efficient catalysts, producing nitroaldols with very high enantiomeric purity (approx. 90–95% ee). This finding contrasts

Palladium-catalyzed three-component radical-polar crossover carboamination of 1,3-dienes or allenes with diazo esters and amines

• Geng-Xin Liu,
• Xiao-Ting Jie,
• Ge-Jun Niu,
• Li-Sheng Yang,
• Xing-Lin Li,
• Jian Luo and
• Wen-Hao Hu

Beilstein J. Org. Chem. 2024, 20, 661–671, doi:10.3762/bjoc.20.59

• experiments indicated that ligand, palladium, light and argon atmosphere were necessary for this transformation (Table 1, entries 2–5). Heating conditions could not facilitate the reaction instead of light conditions (Table 1, entry 6). The efficiency was maintained with another Pd(II) catalyst Pd(PPh3)2Cl2

• (Table 1, entry 7), whereas only low yields of 4a were observed with Pd(0) catalysts Pd(PPh3)4 and Pd2(dba)3 (Table 1, entries 8 and 9). Moreover, adding potassium carbonate as additive failed to furnish 4a, demonstrating that the trace amount of acid from the Pd(II) catalyst may facilitate the formation

• (PPh3)2Cl as catalyst, the model reaction also afforded the corresponding product 4a in 31% yield, demonstrating the H–Pd(II)–X species could be a possible catalytic species (Scheme 4d). According to the UV–visible spectra, the only absorbing species at 467 nm consists in the pre-catalytic system Pd(OAc

Enhanced reactivity of Li⁺@C₆₀ toward thermal [2 + 2] cycloaddition by encapsulated Li⁺ Lewis acid

• Hiroshi Ueno,
• Yu Yamazaki,
• Hiroshi Okada,
• Fuminori Misaizu,
• Ken Kokubo and
• Hidehiro Sakurai

Beilstein J. Org. Chem. 2024, 20, 653–660, doi:10.3762/bjoc.20.58

• acid catalyst; thermal [2 + 2] cycloaddition; Introduction Chemical functionalization of fullerenes is a fascinating and extensively studied approach, playing a pivotal role in fullerene-based materials science to introduce various characteristic functionalities [1][2][3][4][5][6][7]. Significant

• approaches have diligently explored the details of reaction kinetics, quantitatively elucidating the impact of encapsulated Li+ on the reactivity of the outer fullerene cage as a specialized “encapsulated” Lewis acid catalyst [10][11]. While previous studies have revealed valuable insights, such as

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

• expensive, extremely dangerous, strong oxidizing, and even explosive. In this scenario, heteropolyacids emerge as greener and safer alternatives due to their very strong Brønsted acidity. In particular, phosphotungstic acid (HPW) is an economical and green attractive catalyst for being cheap, non-toxic, and

• is known for its chemical and thermal stability. Herein, we report a straightforward approach to the GBB-3CR using HPW as catalyst in ethanol under microwave (μw) heating. This convenient environmentally benign methodology is broad in scope, provides the heterobicyclic products in high yields (up to

• 99%), with a low catalyst loading (2 mol %) in only 30 minutes, and allows the successful use of aliphatic aldehydes, substrates not so frequently explored with most usual catalysts for this reaction. Furthermore, the aforementioned advantages make this methodology very attractive and superior to the