Entry to new spiroheterocycles via tandem Rh(II)-catalyzed O–H insertion/base-promoted cyclization involving diazoarylidene succinimides

• Alexander Yanovich,
• Anastasia Vepreva,
• Ksenia Malkova,
• Grigory Kantin and
• Dmitry Dar’in

Beilstein J. Org. Chem. 2024, 20, 561–569, doi:10.3762/bjoc.20.48

• including aldosterone receptor antagonistic [22], anti-inflammatory [23], and anti-HIV [24] activity. Substantial drugs based on spirocyclic tetrahydrofuran and pyran moieties include spironolactone (a multi-target drug that is primarily used to treat high blood pressure and heart failure) [25

Synthesis of substituted 8H-benzo[h]pyrano[2,3-f]quinazolin-8-ones via photochemical 6π-electrocyclization of pyrimidines containing an allomaltol fragment

• Constantine V. Milyutin,
• Andrey N. Komogortsev,
• Boris V. Lichitsky,
• Mikhail E. Minyaev and
• Valeriya G. Melekhina

Beilstein J. Org. Chem. 2023, 19, 778–788, doi:10.3762/bjoc.19.58

• method for the synthesis of pyrimidines containing an allomaltol unit. The suggested approach is based on the reaction of 2-(1-(dimethylamino)-3-oxo-3-arylprop-1-en-2-yl)-3-hydroxy-6-methyl-4H-pyran-4-ones with cyanamide. The photochemical behavior of the obtained pyrimidines was investigated. It was

• field of terarylenes containing a 3-hydroxy-4-pyranone fragment, in the present communication we investigated the photochemical properties of 2-(4-(4-aryl)-2-(dimethylamino)pyrimidin-5-yl)-6-methyl-4H-pyran-4-ones 9 and 10. It is important to note that the 6π-electrocyclization of 1,3,5-hexatriene

• -hydroxy-6-methyl-4H-pyran-4-ones with cyanamide. Subsequently, the photochemical properties of synthesized pyrimidines were studied. We have demonstrated that a 6π-electrocyclization of the 1,3,5-hexatriene system and subsequent [1,9]-H sigmatropic shift leading to dihydrobenzo[h]pyrano[2,3-f]quinazolines

Asymmetric synthesis of a stereopentade fragment toward latrunculins

• Benjamin Joyeux,
• Antoine Gamet,
• Nicolas Casaretto and
• Bastien Nay

Beilstein J. Org. Chem. 2023, 19, 428–433, doi:10.3762/bjoc.19.32

• precluded the installation of the pyran ring – and the use of its well-known isomerization to set up important stereocenters [6][9] –, thus imposing the anticipated construction of key asymmetric centers. The following discussion will deal with the stereoselective synthesis of a stereopentade amenable to

Investigation of cationic ring-opening polymerization of 2-oxazolines in the “green” solvent dihydrolevoglucosenone

• Solomiia Borova and
• Robert Luxenhofer

Beilstein J. Org. Chem. 2023, 19, 217–230, doi:10.3762/bjoc.19.21

• NMR spectra of the resulting polymers showed significant signals at 6.11–5.92 ppm, 5.93–5.83 ppm, 4.36–4.27 ppm, and 3.92–3.82 ppm. The prepared unsaturated polyacetal was then hydrogenated to give poly(6-ethyl-2,3-dimethoxytetrahydro-2H-pyran). The 1H NMR spectrum of the hydrogenated product showed

A new route for the synthesis of 1-deazaguanine and 1-deazahypoxanthine

• Raphael Bereiter,
• Marco Oberlechner and
• Ronald Micura

Beilstein J. Org. Chem. 2022, 18, 1617–1624, doi:10.3762/bjoc.18.172

• assignments are based on 1H,1H-COSY, 1H,13C-HSQC and 1H,13C-HMBC experiments. High resolution mass spectra were recorded in positive ion mode unless otherwise noted on a Thermo Scientific Q Exactive Orbitrap. 6-Iodo-9-(tetrahydro-2H-pyran-2-yl)-1-deazapurine (17) 6-Iodo-1-deazapurine (2.89 g, 11.79 mmol), p

• -toluenesulfonic acid monohydrate (TsOH·H2O, 0.34 g, 1.77 mmol) and 3,4-dihydro-2H-pyran (2.98 g, 3.21 mL, 35.38 mmol) were dissolved in 5 mL dry N,N-dimethylformamide and stirred overnight for 16 hours at 60 °C. The reaction was quenched by adding ammonia 25% (4 mL) and was stirred for further 5 minutes. The

• gel chromatography using 20 to 50% ethyl acetate in cyclohexane (containing 2% triethylamine) as gradient. Yield: 1.86 g (48%) of compound 17 as a brownish solid. TLC (ethyl acetate/cyclohexane 1:1, 2% NEt3): Rf 0.38; 1H NMR: (400 MHz, DMSO-d6, 25 °C) δ 1.58 (m, 2H, H2-C(5)-pyran), 1.75 (m, 1H, H(b)-C

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

A facile approach to spiro[dihydrofuran-2,3'-oxindoles] via formal [4 + 1] annulation reaction of fused 1H-pyrrole-2,3-diones with diazooxindoles

• Pavel A. Topanov,
• Anna A. Maslivets,
• Maksim V. Dmitriev,
• Irina V. Mashevskaya,
• Yurii V. Shklyaev and
• Andrey N. Maslivets

Beilstein J. Org. Chem. 2022, 18, 1532–1538, doi:10.3762/bjoc.18.162

• investigated for FPDs: the [4 + 2] cycloaddition with alkenes resulting in pyran-annulated products [27][28][29][30][31][32][33][34] and the [3 + 2] cycloaddition with nitrones resulting in isoxazole-annulated products [35][36][37] (Scheme 2). However, formal [4 + 1] cycloaddition reactions for FPDs remain to

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

• ) ppm; 13C NMR (90 MHz, CDCl3) δ 162.5, 148.8, 120.3, 77.4, 76.6, 70.7, 38.7, 22.6, 10.9 ppm; HRMS (m/z): [M + Na]+ calcd 173.0573; found, 173.0572; [α]D20 +132.0 (c 1.0, CH2Cl2). (2R,3S,6RS)-3-Ethyl-2-ethynyl-6-methoxy-3,6-dihydro-2H-pyran (19): This compound was prepared according to reference [18]. A

• pressure. Purification by column chromatography (5% Et2O/pentane), gave 19 as a colourless oil (866 mg, 94%, 91/9 mixture of stereoisomers). Analytical data were in agreement with literature data [18]. (2R,3S,6RS)-3-Ethyl-2-((E)-2-iodovinyl)-6-methoxy-3,6-dihydro-2H-pyran (20): This compound was prepared

A study of the photochemical behavior of terarylenes containing allomaltol and pyrazole fragments

• Constantine V. Milyutin,
• Andrey N. Komogortsev,
• Boris V. Lichitsky and
• Valeriya G. Melekhina

Beilstein J. Org. Chem. 2022, 18, 588–596, doi:10.3762/bjoc.18.61

• two stages: 6π-electrocyclization of 1,3,5-hexatriene systems and subsequent aromatization of the central benzene ring. Among the significant diversity of terarylenes, compounds containing a 5-hydroxy-2-methyl-4H-pyran-4-one (allomaltol) fragment are of particular interest. For such systems two types

• pyran-4-one substituent, 6π-electrocyclization of 1,3,5-hexatriene system does not occur (Scheme 2). As it was demonstrated earlier [26], UV irradiation of terarylenes containing oxazolone and 3-hydroxypyran-4-one fragments 9 can lead to two types of photoprocesses. Based on the aforementioned results

Synthesis of sulfur karrikin bioisosteres as potential neuroprotectives

• Martin Pošta,
• Václav Zima,
• Lenka Poštová Slavětínská,
• Marika Matoušová and
• Petr Beier

Beilstein J. Org. Chem. 2022, 18, 549–554, doi:10.3762/bjoc.18.57

• -b]furan-2-one, has been recently identified as an extremely efficient neuroprotective butenolide. Herein, we report the targeted synthesis of this compound as well as new synthetic protocols toward a class of compounds derived from 2H-furo[2,3-c]pyran-2-ones (karrikins) via bioisosteric exchange of

• concentrations [11][12][13][14]. Structurally, the karrikin backbone consists of a fused pyran and a furanone ring. Each particular molecule differs in the number of methyl groups in positions C3, C5 and C7. Structures of the four most active and abundant karrikins (KAR1–KAR4) are depicted in Figure 1. The

• synthesis of these heterocycles is rather challenging, because the fused pyran and furanone system cannot be easily prepared by standard cyclization methods [15][16][17]. Although karrikins are extremely active plant growth regulators [14][18][19], their biological activity in humans was not investigated

Advances in mercury(II)-salt-mediated cyclization reactions of unsaturated bonds

• Sumana Mandal,
• Raju D. Chaudhari and
• Goutam Biswas

Beilstein J. Org. Chem. 2021, 17, 2348–2376, doi:10.3762/bjoc.17.153

• , or mercuric trifluoroacetate as shown in Scheme 41 [97]. Alkyne carboxylic acids also undergo oxymercuration reactions to form furan- and pyran-like derivatives. When γ-alkyne carboxylic derivative 140 was refluxed with HgO the cyclization took place to give product 141 in almost quantitative yields

• ) [101]. Later it was shown that alkynyl diol 150 when treated with 20 mol % Hg(OTf)2 followed by Et3SiH afforded bispyranoyl ketone 151, but when Hg(OTf)2 was increased (1 equiv) then fused pyran-oxocane derivative 152 was isolated [102]. Six-membered morpholine derivatives were also synthesized by

• acids and alcohol to furan, pyran, and spirocyclic derivatives. Hg(II)-salt-mediated cyclization of 1,4-dihydroxy-5-alkyne derivatives. Six-membered morpholine derivative formation by catalytic Hg(II)-salt-induced cyclization. Hg(OTf)2-catalyzed hydroxylative carbocyclization of 1,6-enyne. a) Hg(OTf)2

Prins cyclization-mediated stereoselective synthesis of tetrahydropyrans and dihydropyrans: an inspection of twenty years

• Asha Budakoti,
• Pradip Kumar Mondal,
• Prachi Verma and
• Jagadish Khamrai

Beilstein J. Org. Chem. 2021, 17, 932–963, doi:10.3762/bjoc.17.77

• a (Z)-olefin. The addition of ZnCl2·Et2O and (MeO)3CH to the resulting homoallylic alcohol 247 leads to the desired pyran derivative 248, having an acetal group at the C2 position (Scheme 58). By treatment of acetal 248 with allyltrimethylsilane gave 2,6-anti-configured THP 249 as a single

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

• ylide formation over the expected Strecker degradation. The azomethine ylide trapped by 3-alkenylindole undergoes 1,3-dipolar cycloaddition and led to the cycloadducts 44. 4 Pyrans Pyran is a six-membered heterocyclic, non-aromatic ring, consisting of five carbon atoms and one oxygen atom with two

• double bonds. Numerous natural compounds containing pyrans and benzopyrans (fused pyrans) are identified. Epicalyxin (45) is used as an anticancer agent against human HT-1080 fibrosarcoma and murine 26-L5 carcinoma. Laninamivir (46) is a pyran-based drug used as a neuraminidase inhibitor and zanamivir

Recent progress in the synthesis of homotropane alkaloids adaline, euphococcinine and N-methyleuphococcinine

• Dimas J. P. Lima,
• Antonio E. G. Santana,
• Michael A. Birkett and
• Ricardo S. Porto

Beilstein J. Org. Chem. 2021, 17, 28–41, doi:10.3762/bjoc.17.4

• a 6-step sequence from 3,4-dihydro-2-ethoxy-2H-pyran (58) [50]. Treatment of 58 with a mixture of butyllithium and potassium tert-butoxide in the presence of TMEDA and pentane, followed by reaction with the corresponding alkyl iodides in THF, and finally, acidic cleavage of the generated acetal

Ring-closing metathesis of prochiral oxaenediynes to racemic 4-alkenyl-2-alkynyl-3,6-dihydro-2H-pyrans

• Viola Kolaříková,
• Markéta Rybáčková,
• Martin Svoboda and
• Jaroslav Kvíčala

Beilstein J. Org. Chem. 2020, 16, 2757–2768, doi:10.3762/bjoc.16.226

• with CH2Cl2, and the organic solution was carefully evaporated to give the crude products. If necessary, the products were purified by column chromatography. 4-Ethenyl-(2-prop-2-yn-1-yl)-3,6-dihydro-2H-pyran (12a) According to general procedure A, from oxaenediyne 2a (243 mg, 1.64 mmol) in CH2Cl2 (6 mL

• ), 137.9 (s, 1C, CH=CH2); MS (CI+, m/z): 149.1 [M + H]+ (10), 109.1 [M − C3H3]+ (100), 91.1 [C7H7]+ (45), 81.1 [C5H5O]+ (50); HRMS (CI+, m/z): [M + H]+ calcd for C10H13O, 149.0966; found, 149.0964. 2-(But-2-yn-1-yl)-4-(prop-1-en-2-yl)-3,6-dihydro-2H-pyran (12b) According to general procedure A, from

• − CH2=O + H+]+ (95), 121.1 [M − CH2=O − CH≡CH + H]+ (100); HRMS (EI+, m/z): [M]+ calcd for C12H16O, 176.1201; found, 176.1208. 4-(But-1-en-2-yl)-2-(pent-2-yn-1-yl)-3,6-dihydro-2H-pyran (12c) According to general procedure A, from oxaenediyne 2c (31 mg, 0.15 mmol) in CH2Cl2 (1.2 mL) using G-I (6.2 mg

Convenient access to pyrrolidin-3-ylphosphonic acids and tetrahydro-2H-pyran-3-ylphosphonates with multiple contiguous stereocenters from nonracemic adducts of a Ni(II)-catalyzed Michael reaction

• Alexander N. Reznikov,
• Dmitry S. Nikerov,
• Anastasiya E. Sibiryakova,
• Victor B. Rybakov,
• Evgeniy V. Golovin and
• Yuri N. Klimochkin

Beilstein J. Org. Chem. 2020, 16, 2073–2079, doi:10.3762/bjoc.16.174

• ,6R)-13b. Intermolecular N-methylation of reduction product 7. Synthesis of pyrrolidinyl phosphonic acids 11a–d. Synthesis of tetrahydropyranylphosphonates 13a–f via diastereoselective Henry/acetalyzation reaction. Synthesis of (3,4-dihydro-2H-pyran-5-yl)phosphonate 14. Optimization of the conditions

Syntheses of spliceostatins and thailanstatins: a review

• William A. Donaldson

Beilstein J. Org. Chem. 2020, 16, 1991–2006, doi:10.3762/bjoc.16.166

• ) gave the C-phenyl glucoside 75 [36]. Notably, the use of oxidants other than BQ gave either the TMS enol ether or the 2,3-dihydro-6-phenyl-4H-pyran-4-one. The C-3 exocyclic methylene group was introduced by a Wittig olefination, and after the manipulation of the protecting groups, a VO(acac)2-catalyzed

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

• Federation Lomonosov Moscow State University, Moscow 119991, Russian Federation 10.3762/bjoc.15.277 Abstract The condensation of primary amines with N-(1-(4-hydroxy-6-methyl-2-oxo-2H-pyran-3-yl)-2-oxo-2-arylethyl)acetamides was explored. Thus, a previously unknown recyclization of the starting material was

• strongly desirable. In this article, we describe a convenient synthetic method for the preparation of 6-alkyl-2-methyl-7-aryl-6,7-dihydro-1H-pyrrolo[3,4-b]pyridine-4,5-diones 1. Therein, the condensation of N-(1-(4-hydroxy-6-methyl-2-oxo-2H-pyran-3-yl)-2-oxo-2-arylethyl)acetamides 2 with a diverse range of

• 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

Catalytic asymmetric oxo-Diels–Alder reactions with chiral atropisomeric biphenyl diols

• Chi-Tung Yeung,
• Wesley Ting Kwok Chan,
• Wai-Sum Lo,
• Ga-Lai Law and
• Wing-Tak Wong

Beilstein J. Org. Chem. 2019, 15, 955–962, doi:10.3762/bjoc.15.92

• diene in standard conditions. The reaction was found to be very sluggish when performed at −40 °C. However, at −20 °C, better yields were obtained. The reactions with organocatalysts 1–4 showed moderate yields (41–64%) of the catalytic product (2,3-dihydro-2-phenyl-4H-pyran-4-one). Unfortunately

• used as catalysts (Table 1, entries 8–11). With 1, the yield and enantioselectivity of the catalytic product (2,3-dihydro-2-tert-butyl-4H-pyran-4-one) were 50% and 12% ee (Table 1, entry 8). The reactivity and enantioselectivity were significantly increased to 66% yield and 72% ee when 2 was employed

Synthesis of the aglycon of scorzodihydrostilbenes B and D

• Katja Weimann and
• Manfred Braun

Beilstein J. Org. Chem. 2019, 15, 610–616, doi:10.3762/bjoc.15.56

• , 152.5, 154.6, 158.1, 205.2; ESIMS m/z (%): 377.2 [M + 1] (100); HRMS (ESI): [M + H]+ calcd for C24H25O4, 377.1753; found, 377.1748. (2R,3R,4S,5R,6R)-2-(Acetoxymethyl)-6-[3-acetyl-2-(3,4-dimethoxyphenethyl)-4-hydroxyphenoxy]tetrahydro-2H-pyran-3,4,5-triyl triacetate (12): A 50 mL two-necked flask was

Ring-closing-metathesis-based synthesis of annellated coumarins from 8-allylcoumarins

• Christiane Schultze and
• Bernd Schmidt

Beilstein J. Org. Chem. 2018, 14, 2991–2998, doi:10.3762/bjoc.14.278

• completely in this case (Table 4, entries 3 and 4). The beneficial effect of low initial substrate concentrations on RCM reactions with acrylates has previously been described [65] and was later systematically investigated by one of us [66]. A possible access to the pyran-2-one-annellated coumarin

• catalyze allylic and benzylic oxidation reactions through a radical mechanism [70]. To implement this tandem sequence in the synthesis of pyran-2-one-annellated coumarins 15 an isomerization of the 8-allyl substituent to a prop-1-enyl substituent was first required. When 8-allyl-7-hydroxycoumarin (8a) was

• -1-enyl)coumarins 16 were isolated in high overall yields and E-selectivities. Allylation of phenols 16 furnished the RCM precursors 17, which underwent the tandem RCM/allylic oxidation sequence to compounds 15 in fair yields (Table 5). All pyran-2-one-annellated coumarins 15 synthesized in the

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

An overview on recent advances in the synthesis of sulfonated organic materials, sulfonated silica materials, and sulfonated carbon materials and their catalytic applications in chemical processes

• Hashem Sharghi,
• Pezhman Shiri and
• Mahdi Aberi

Beilstein J. Org. Chem. 2018, 14, 2745–2770, doi:10.3762/bjoc.14.253

• -sulfo-1,4-diazabicyclo[2.2.2]octane-1,4-diium) chloride (C4(DABCO-SO3H)2·4Cl, 31) and its applications in the synthesis of spiro-oxindole derivatives 36 and 37 was described. C4(DABCO-SO3H)2·4Cl 31 acted as an efficient, cheap, and reusable nanocatalyst for synthesis of 2-amino-4H-pyran derivatives 36

• homogeneous conditions (Scheme 5). After this successful application, catalyst 31 was tested in the synthesis of bis(2-amino-4H-pyran) derivatives 39–44 via a one-pot multicomponent reaction of dialdehydes 38 (instead of isatin and acenaphthenequinone substrates), a variety of C–H activated acids 20a,b, 23

• , 34a–c and malononitrile (35) under the same reaction conditions. The observations showed that bis(2-amino-4H-pyran) derivatives 39–44 are constructed in excellent yields during very short reaction times with a higher amount of the catalyst (4 mol %, Scheme 6). The recyclability of this homogeneous

Ring-opening metathesis of some strained bicyclic systems; stereocontrolled access to diolefinated saturated heterocycles with multiple stereogenic centers

• Zsanett Benke,
• Melinda Nonn,
• Márton Kardos,
• Santos Fustero and
• Loránd Kiss

Beilstein J. Org. Chem. 2018, 14, 2698–2707, doi:10.3762/bjoc.14.247

• , 100 MHz) δ 21.4, 25.3, 28.4, 46.8, 55.6, 78.7, 79.8, 125.9, 129.0, 154.6, 173.0; MS (ESI, pos) (m/z): 288 [M + 1], 168 [M – Boc]; anal. calcd for C14H21NO4: C, 62.90; H, 7.92; N, 5.24; found, C, 63.22; H, 7.59; N, 4.88. tert-Butyl ((S*)-1-((3R*,6S*)-2-oxo-6-vinyltetrahydro-2H-pyran-3-yl)but-3-en-1-yl

Synthesis of pyrimido[1,6-a]quinoxalines via intermolecular trapping of thermally generated acyl(quinoxalin-2-yl)ketenes by Schiff bases

• Svetlana O. Kasatkina,
• Ekaterina E. Stepanova,
• Maksim V. Dmitriev,
• Ivan G. Mokrushin and
• Andrey N. Maslivets

Beilstein J. Org. Chem. 2018, 14, 1734–1742, doi:10.3762/bjoc.14.147

• quinoxalin-2-ylideneacetates [9], multicomponent Mannich–Ritter transformations of quinoxalin-2(1H)-ones under the action of nitriles and 3,4-dihydro-2H-pyran [10] and a microwave-assisted cascade strategy via in situ-generated N-acyliminium ion precursors and amines [11] (Figure 2). To develop a new