Functionalization of imidazole N-oxide: a recent discovery in organic transformations

• Koustav Singha,
• Imran Habib and
• Mossaraf Hossain

Beilstein J. Org. Chem. 2022, 18, 1575–1588, doi:10.3762/bjoc.18.168

• imidazole 1-oxides. The selected CH-acids to study the scope of substrates were barbituric acid, dimedone, 4-hydroxy-6-methyl-2H-pyran-2-one, 1,3-dimethylbarbituric acid, 4-hydroxycoumarin, and 1,3-indandione. The nature of the CH-acids and 2-unsubstituted imidazole N-oxides did not affect the yield of

• -oxide 32 (2 mmol), aldehyde 33 (2 mmol) and CH acid 34 (2 mmol, barbituric acid) was refluxed in H2O (2 mL) and MeCN (5 mL) solvent mixture for 8 h. bThe mixture of imidazole N-oxide 32 (2 mmol), CH-acid 34 (2 mmol, dimedone, 4-hydroxy-6-methyl-2H-pyran-2-one, 1,3-dimethylbarbituric acid, 4

Preparation of an advanced intermediate for the synthesis of leustroducsins and phoslactomycins by heterocycloaddition

• Anaïs Rousseau,
• Guillaume Vincent and
• Cyrille Kouklovsky

Beilstein J. Org. Chem. 2022, 18, 1385–1395, doi:10.3762/bjoc.18.143

• 206.6, 154.9, 85.1, 82.3, 59.0, 45.0, 36.5, 32.2, 28.4, 18.1, 12.1 ppm; HRMS (m/z): [M + Na]+ calcd 424.2490; found, 424.2480; [α]D20 +37.4 (c 0.5, CH2Cl2). (5S,6R)-5-Ethyl-6-ethynyl-5,6-dihydro-2H-pyran-2-one (21): Caesium fluoride (290 mg, 1.91 mmol, 1.3 equiv) was added to a solution of the lactone

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

• -methyl-2H-pyran-2-one and arylglyoxal to form intermediate A. Michael addition of amine to intermediate A gives B which further undergoes an intramolecular nucleophilic addition reaction to yield C which on cyclization and with subsequent loss of water from D produce the desired products 34. Meshram and

One-pot synthesis of substituted pyrrolo[3,4-b]pyridine-4,5-diones based on the reaction of N-(1-(4-hydroxy-6-methyl-2-oxo-2H-pyran-3-yl)-2-oxo-2-arylethyl)acetamide with amines

• Valeriya G. Melekhina,
• Andrey N. Komogortsev,
• Boris V. Lichitsky,
• Vitaly S. Mityanov,
• Artem N. Fakhrutdinov,
• Arkady A. Dudinov,
• Vasily A. Migulin,
• Yulia V. Nelyubina,
• Elizaveta K. Melnikova and
• Michail M. Krayushkin

Beilstein J. Org. Chem. 2019, 15, 2840–2846, doi:10.3762/bjoc.15.277

• amines 3 did not only furnish the desired scaffolds in satisfactory yields but also allowed to use a variety of readily available substituted substrates (Scheme 1). Results and Discussion The published synthesis of acetamides 2 includes a one-pot three-component reaction of 4-hydroxy-6-methyl-2H-pyran-2

• -one (4), arylglyoxals 5, and acetamide (6) using SnCl2–SiO2 nanoparticles as heterogeneous catalyst under solvent-free conditions [10]. However, as we found out, the use of a catalyst was unnecessary for this transformation. In turn, refluxing the reaction mixture in acetonitrile was sufficient for

Volatiles from the hypoxylaceous fungi Hypoxylon griseobrunneum and Hypoxylon macrocarpum

• Jan Rinkel,
• Alexander Babczyk,
• Tao Wang,
• Marc Stadler and
• Jeroen S. Dickschat

Beilstein J. Org. Chem. 2018, 14, 2974–2990, doi:10.3762/bjoc.14.277

• germination and to cause necrotic lesions in the plant tissue. In other cases, fungal volatiles can have beneficial effects and may even be involved in the induction of systemic resistance in plants, as can be assumed for 6-pentyl-2H-pyran-2-one (5) that is produced by many fungi from the genus Trichoderma

• ) 152.9 (Cq), 152.8 (Cq), 143.5 (Cq), 124.7 (CH), 124.3 (Cq), 108.0 (CH), 60.6 (CH3), 60.3 (CH3), 55.8 (CH3), 15.9 (CH3). Structures of fungal volatiles. Trichodiene (1), aristolochene (2), (R)-oct-1-en-3-ol (3), 3,4-dimethylpentan-4-olide (4), and 6-pentyl-2H-pyran-2-one (5). Total ion chromatogram of a

Volatiles from the xylarialean fungus Hypoxylon invadens

• Jeroen S. Dickschat,
• Tao Wang and
• Marc Stadler

Beilstein J. Org. Chem. 2018, 14, 734–746, doi:10.3762/bjoc.14.62

• , Agaricus bisporus, and other delicacies from the fungal world such as the oyster mushroom, the penny bun, and shiitake [2][3]. The ecological function of most fungal volatiles is unknown, but for the alcohol 1 (Figure 1) a germination inhibitory function has been reported [4]. For 6-pentyl-2H-pyran-2-one

• ; MS (EI, 70 eV) m/z (%): 218 (81) [M]+, 204 (13), 203 (100), 137 (53), 136 (17), 108 (21), 67 (26), 43 (23), 39 (13). Structures of the widespread fungal volatiles oct-1-en-3-ol (1) and 6-pentyl-2H-pyran-2-one (2), the stereoisomers α-muurolene (3), α-amorphene (4) and α-cadinene (5), and the

Electrochemical Corey–Winter reaction. Reduction of thiocarbonates in aqueous methanol media and application to the synthesis of a naturally occurring α-pyrone

• Ernesto Emmanuel López-López,
• José Alvano Pérez-Bautista,
• Fernando Sartillo-Piscil and
• Bernardo A. Frontana-Uribe

Beilstein J. Org. Chem. 2018, 14, 547–552, doi:10.3762/bjoc.14.41

• convert thiocarbonates derived from 1,2-diols containing the 6-pentyl-2H-pyran-2-one framework to trans-alkenes by means of electrochemical reduction in an H-type separated cell was developed. The thiocarbonate functional group can be reduced using a vitreous carbon electrode in MeOH/H2O 80:20 with AcOH

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

Volatiles from the tropical ascomycete Daldinia clavata (Hypoxylaceae, Xylariales)

• Tao Wang,
• Kathrin I. Mohr,
• Marc Stadler and
• Jeroen S. Dickschat

Beilstein J. Org. Chem. 2018, 14, 135–147, doi:10.3762/bjoc.14.9

• natural product is 6-nonyl-2H-pyran-2-one. The antimicrobial and cytotoxic effects of the synthetic volatiles are also reported. Keywords: enantioselective synthesis; gas chromatography; mass spectrometry; natural products; volatiles; Introduction A large variety of volatile organic compounds from

• widespread fungal volatile is 6-pentyl-2H-pyran-2-one (2) that was first isolated from Trichoderma and exhibits a strong coconut aroma [5]. For fungi producing 2 a plant-growth promoting effect and an induction of systemic resistance in plants has been observed which makes these fungi interesting as

• . clavata, showed a mass spectrum that was not included in our database (Figure 5A). However, the mass spectrum of 6-propyl-5,6-dihydro-2H-pyran-2-one (Figure 5B) is very similar, and the mass difference for the molecular ion of 28 Da suggested the structure of 6-methyl-5,6-dihydro-2H-pyran-2-one for

Rh-Catalyzed reductive Mannich-type reaction and its application towards the synthesis of (±)-ezetimibe

• Motoyuki Isoda,
• Kazuyuki Sato,
• Yurika Kunugi,
• Satsuki Tokonishi,
• Atsushi Tarui,
• Masaaki Omote,
• Hideki Minami and
• Akira Ando

Beilstein J. Org. Chem. 2016, 12, 1608–1615, doi:10.3762/bjoc.12.157

• imine 1B and 5,6-dihydro-2H-pyran-2-one (2h) (Table 2). Unfortunately, the reaction conditions as above gave a complex mixture that did not contain the desired products as shown in Table 2, entry 1. Heating the reaction mixture at 80 °C gave β-aminolactone 4Bh in a very low yield (Table 2, entry 2

• ) was added to the mixture and stirred for 30 min at the same temperature. Subsequently, 5,6-dihydro-2H-pyran-2-one (2, 1.2 equiv) was added to the mixture and then 1.0 M Et2Zn in hexane (3 equiv) was gradually added to the mixture at room temperature, and the mixture was stirred for 24 h. The mixture

Biosynthesis of oxygen and nitrogen-containing heterocycles in polyketides

• Franziska Hemmerling and
• Frank Hahn

Beilstein J. Org. Chem. 2016, 12, 1512–1550, doi:10.3762/bjoc.12.148

• -hydroxytetrahydro-2H-pyran-2-one 124 is formally dehydrated by consecutive malonylation–elimination to finally give a 5,6-dihydro-2H-pyran-2-one 127 [127]. The tailoring enzyme PlmT2 was proposed to catalyse the decarboxylative elimination of malonoyl halfester 126. It is not clear, whether the initial malonylation

• was catalysed by an AT domain or another enzyme in the cluster. Similar chemistry occurs during the biosynthesis of related compounds like fostriecin and leptomycin [128][129]. In jerangolid A biosynthesis, the dihydro-2H-pyran-2,4(3H)-dione 128 is transformed into a 4-methoxy-5,6-dihydro-2H-pyran-2

• -one 129 by action of the O-methyltransferase JerF [50]. 1.6.2 Michael addition–lactonisation: A novel mechanism for the integration of pyran-2-ones into polyketide backbones has recently been discovered. Rhizoxin. In 2013, Hertweck and co-workers provided detailed insight into the unprecedented enzyme

Biosynthesis of α-pyrones

• Till F. Schäberle

Beilstein J. Org. Chem. 2016, 12, 571–588, doi:10.3762/bjoc.12.56

• -pyrone derivatives for their antimicrobial and cytotoxic properties [2]. The volatile α-pyrone 5-(2,4-dimethylheptyl)-3-methyl-2H-pyran-2-one (7, Figure 1), also named supellapyrone) is used by female brownbanded cockroaches to attract males [13]. It is known that cockroaches use pheromones in many

• -pyran-2-one (47, Figure 10) [52]. Also antitumor activities of α-pyrones had been shown. Thus, pironetin (47, Figure 10) induced apoptosis in a dose- and time-dependent manner, and tubulin assembly was inhibited in vitro [53]. The natural product was isolated from Streptomyces sp. NK10958 [54], and its

• aspects of influencing interacting behavior between individuals. Hence, such volatiles are used in courtship behavior to find mating partners. Also another α-pyrone fulfilling pheromone function in insects is known, i.e., the queen recognition pheromone of the red imported fire ant, 6-(1-pentenyl)-2H

Multicomponent reactions in nucleoside chemistry

• Mariola Koszytkowska-Stawińska and
• Włodzimierz Buchowicz

Beilstein J. Org. Chem. 2014, 10, 1706–1732, doi:10.3762/bjoc.10.179

• (59a) (X = NH) [92], the N-methyl-4-hydroxy-6-methylpyridin-2(1H)-one (59b) (X = NMe) [92], N-ethyl-4-hydroxy-6-methylpyridin-2(1H)-one (59c) (X = NEt) [92], 4-hydroxy-6-methyl-2H-pyran-2-one (59d) (X = O) [92], or cyclohexane-1,3-dione (60) [93]. The syntheses of derivatives 61 to 64 represent a

Visible-light-induced, Ir-catalyzed reactions of N-methyl-N-((trimethylsilyl)methyl)aniline with cyclic α,β-unsaturated carbonyl compounds

• Dominik Lenhart and
• Thorsten Bach

Beilstein J. Org. Chem. 2014, 10, 890–896, doi:10.3762/bjoc.10.86

• . With 5,6-dihydro-2H-pyran-2-one (12) two major products 13 and 14 could be isolated (Scheme 3). If performed in CH2Cl2 the reaction remained incomplete after 24 hours. The substrate was recovered in 20% and products 13 and 14 were obtained in a ratio of 55/45 with the tricyclic product prevailing. A

• higher type selectivity. The domino process was suppressed and the plain addition product 22 was obtained in 75% yield (Scheme 7). The latter result suggested that the previously discussed (Scheme 3) addition reaction to 5,6-dihydro-2H-pyran-2-one (12) might also lead to a single product if performed

• -dihydro-2H-pyran-2-one (12). Ir-catalyzed addition reactions of N-methyl-N-((trimethylsilyl)methyl)aniline (5) to 2-cyclopentenone (15). Ir-catalyzed formation of tricyclic products 19 by a domino radical addition reaction to α,β-unsaturated lactams 18. Ir-catalyzed addition reactions of N-methyl-N

Direct alkenylation of indolin-2-ones by 6-aryl-4-methylthio-2H-pyran-2-one-3-carbonitriles: a novel approach

• Sandeep Kumar,
• Ramendra Pratap,
• Abhinav Kumar,
• Brijesh Kumar,
• Vishnu K. Tandon and
• Vishnu Ji Ram

Beilstein J. Org. Chem. 2013, 9, 809–817, doi:10.3762/bjoc.9.92

• , Lucknow-226001, India 10.3762/bjoc.9.92 Abstract A direct one-pot base-induced alkenylation of indolin-2-ones has been developed by using 6-aryl-4-methylthio-2H-pyran-2-one-3-carbonitriles. Different bases such as MeONa, NaH and t-BuONa have been used to optimize the reaction conditions to obtain the

• ; 2H-pyran-2-one; Introduction 6-Aryl-4-methylthio-2H-pyran-2-one-3-carbonitriles have emerged as versatile synthons for the construction of an array of arenes and heteroarenes through base-induced ring transformation by nitrogen, sulfur and carbon nucleophiles [1]. However, suitably functionalized 2H

• demanding and remains a challenge to the state-of-art synthesis. The promising pharmacological activities of 3-alkenylindolin-2-ones, prompted us to develop an efficient and concise route for their construction. Based on the topography and electronic features of 6-aryl-4-methylthio-2H-pyran-2-one-3

Pd/C-mediated synthesis of α-pyrone fused with a five-membered nitrogen heteroaryl ring: A new route to pyrano[4,3-c]pyrazol-4(1H)-ones

• Dhilli Rao Gorja,
• Venkateswara Rao Batchu,
• Ashok Ettam and
• Manojit Pal

Beilstein J. Org. Chem. 2009, 5, No. 64, doi:10.3762/bjoc.5.64

• ] (or 2H-pyran-2-one) and their benzo derivatives, e.g. isocoumarins [3], have shown a wide range of pharmacological activities [4][5][6] such as antifungal, antimicrobial, phytotoxic and other effects. On the other hand α-pyrones fused with a five-membered heteroaryl ring, e.g. thienopyranones, have

A short stereoselective synthesis of (+)-(6R,2′S)-cryptocaryalactone via ring- closing metathesis

• Palakodety Radha Krishna,
• Krishnarao Lopinti and
• K. L. N. Reddy

Beilstein J. Org. Chem. 2009, 5, No. 14, doi:10.3762/bjoc.5.14

• the sub-classes of these 5,6-dihydro-2H-pyran-2-one compounds is the styryl lactones which possess a styryl moiety side chain. The styryl moiety of goniothalamin has been shown to be of importance for its cytotoxic effect on different cancer cells as well as its antimicrobial, larvicidal activity and

• also isolated from C. bourdilloni, C. moschata and C. myrtifolia and their absolute configuration was established [34]. These cryptocaryalactones are natural germination inhibitors with no effect on corn [35]. We were interested in synthesizing natural products containing 5,6-dihydro-2H-pyran-2-one