Polyketide stereocontrol: a study in chemical biology

• Kira J. Weissman

Beilstein J. Org. Chem. 2017, 13, 348–371, doi:10.3762/bjoc.13.39

• reactions present in trans-AT PKSs and certain cis-AT PKSs (for example, pyran synthase domains [19][20], double bond shifting modules [21][22], C-2-hydroxylases [11], etc.) can also have stereochemical consequences, but these will not be treated here as little is known to date about the enzymatic factors

A new paradigm for designing ring construction strategies for green organic synthesis: implications for the discovery of multicomponent reactions to build molecules containing a single ring

• John Andraos

Beilstein J. Org. Chem. 2016, 12, 2420–2442, doi:10.3762/bjoc.12.236

• dihydropyridine, hydantoin, imidazole, indole, isoquinoline, isoxazole, oxazole, 4H-pyran, pyrazine, pyridazine, pyridine, pyridinone, pyrimidine, pyrimidone, pyrrole, 3H-quinazolin-4-one, quinoline, 1H-quinolin-4-one, and thiophene. For heterocycles that are composed of a fused aromatic ring, such as

Diastereoselective synthesis of 3,4-dihydro-2H-pyran-4-carboxamides through an unusual regiospecific quasi-hydrolysis of a cyano group

• Mikhail Yu. Ievlev,
• Oleg V. Ershov,
• Mikhail Yu. Belikov,
• Angelina G. Milovidova,
• Viktor A. Tafeenko and
• Oleg E. Nasakin

Beilstein J. Org. Chem. 2016, 12, 2093–2098, doi:10.3762/bjoc.12.198

• University, Leninskie gory 1, Moscow, Russia 10.3762/bjoc.12.198 Abstract An efficient diastereoselective approach for the synthesis of functionalized 3,4-dihydro-2H-pyran-4-carboxamides with variable frame was developed based on the reaction of available 4-oxoalkane-1,1,2,2-tetracarbonitriles (adducts of

• TCNE and ketones) with aldehydes in an acidic media. An unusual process of quasi hydrolysis of the cyano group was observed in the course of the described regio- and diastereoselective transformation. Keywords: diastereoselectivity; 3,4-dihydro-2H-pyran-4-carboxamide; nitriles; pyran; quasi-hydrolysis

• influenza caused by influenza A and B viruses contain a 3,4-dihydro-2H-pyran fragment [5]. Moreover, dihydropyrans have been proven to be particularly useful in the preparation of cyclic components of macrocyclic antibiotics [6][7] and as precursors in the synthesis of C-glycosides [8]. Modern and

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

• precursor and thus particular ring systems [9][10][11]. Most heterocycles in polyketides are formed by specialised PKS domains and tailoring enzymes. These can be active during assembly of the nascent PKS precursor (as for example in the case of pyran/furan formation via oxa-Michael addition, see chapters

• formation of up to two new stereocentres. Its appearance in several polyketide biosynthetic pathways was proposed for a decade based on gene cluster analysis. An in vitro characterisation of responsible catalytic units has however only recently been achieved. Two pyran-forming cyclase domains were

• characterised in the pederin (24) and the ambruticin (28) biosynthetic pathways (Scheme 3 and Scheme 4) [14][15]. PedPS7 is a monofunctional pyran synthase (PS) domain that was predicted to catalyse ring formation from an α,β-unsaturated intermediate in the biosynthesis of the PKS–NRPS hybrid product pederin

Indenopyrans – synthesis and photoluminescence properties

• Andreea Petronela Diac,
• Ana-Maria Ţepeş,
• Albert Soran,
• Ion Grosu,
• Anamaria Terec,
• Jean Roncali and
• Elena Bogdan

Beilstein J. Org. Chem. 2016, 12, 825–834, doi:10.3762/bjoc.12.81

• Moltech-Anjou, University of Angers, 2 Boulevard Lavoisier 49045 Angers, France 10.3762/bjoc.12.81 Abstract New indeno[1,2-c]pyran-3-ones bearing different substituents at the pyran moiety were synthesized and their photophysical properties were investigated. In solution all compounds were found to be

• heterocycles consisting of fused indene and pyran units. Generally, oxygen-containing heteroaromatic compounds have been encountered as biologically active molecules and display exciting physico-chemical properties. Therefore, these compounds have found many applications in medicinal chemistry and material

• context are benzo[b]indeno-[2,1-e]pyran-10,11-diones, which stimulate the biosynthesis of erythropoietin and are used to treat anemia [10]. Another application includes the use of some amino-spiroindenopyran derivatives as selective sensors for thallium(I) ions in human urine [11]. Pyran-containing

Scope and mechanism of the highly stereoselective metal-mediated domino aldol reactions of enolates with aldehydes

• M. Emin Cinar,
• Bernward Engelen,
• Martin Panthöfer,
• Hans-Jörg Deiseroth,
• Jens Schlirf and
• Michael Schmittel

Beilstein J. Org. Chem. 2016, 12, 813–824, doi:10.3762/bjoc.12.80

• aldehydes in the presence of metal halides to furnish tetrahydro-2H-pyran-2,4-diols in a highly diastereoselective manner, is investigated thoroughly by experiments and computations. The reaction was also successfully implemented on a flow micro reactor system. Keywords: DFT; diastereoselective reaction

• the years [31]. We have already reported a domino aldol–aldol–hemiacetal process that furnishes racemic tetrahydro-2H-pyran-2,4-diols in a highly stereoselective manner (Scheme 1) [30][31][32][33][34][35][36][37]. In this paper, the domino aldol–aldol–hemiacetal reaction involving several metals (Al

• groups, whose probability of allocation at C2 and C6 is 0.5, respectively, appear to be attached to the pyran ring. This can easily be explained by the superposition of two enantiomers which are statistically and isoconformationally incorporated in the crystal lattice. Separation of two enantiomers was

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

• plant pathogenic fungus Hymenoscyphus pseudoalbidus, which inhibited germination of Fraxinus excelsior (European ash) seeds [60]. In contrast, 3-methyl-2H-furo[2,3-c]pyran-2-one, a component of smoke derived from burning plant material, promotes seed germination [61]. Recently, a further regulatory

(Thio)urea-mediated synthesis of functionalized six-membered rings with multiple chiral centers

• Giorgos Koutoulogenis,
• Nikolaos Kaplaneris and
• Christoforos G. Kokotos

Beilstein J. Org. Chem. 2016, 12, 462–495, doi:10.3762/bjoc.12.48

• formation of substituted dihydro-2H-pyran-6-carboxylate 3 (Scheme 4) [16]. It was observed, that by employing PhCOOH as an additive, the yield (%) and the ee (%) increased, in comparison to the use of 4-dimethylaminopyridine (DMAP). A single example was shown leading to 82% yield and an enantiomeric excess

• same nucleophile 81, Wang and his group combined it with β,γ-unsaturated α-ketoesters 87, as the electrophile, catalyzed by bifunctional indane-derived thiourea 88, to produce derivatives of 3,4-dihydro-2H-pyran 89 (Scheme 30) [49]. This reaction sequence involved a Michael reaction, followed by a

• McGarrigle, Galan and co-workers (Scheme 77) [96]. In this reaction the reagent is 2,3,4-trisubstituted dihydro-pyran 247 and the product is the corresponding α-galactopyranose 248. This reaction provides exclusively the α-diastereomer in a yield up to 98%. In 2013, Schmidt and co-workers described the use

Natural products from microbes associated with insects

• Christine Beemelmanns,
• Huijuan Guo,
• Maja Rischer and
• Michael Poulsen

Beilstein J. Org. Chem. 2016, 12, 314–327, doi:10.3762/bjoc.12.34

• moiety with a pyran ring. A follow-up study via genomic analysis and metabolomic profiles revealed that piperazic acid-containing cyclic depsipeptides are very common in this ecological niche of ant-associated bacteria. Fermentation and purification of metabolite extracts of three ant-associated

Copper-catalysed asymmetric allylic alkylation of alkylzirconocenes to racemic 3,6-dihydro-2H-pyrans

• Emeline Rideau and
• Stephen P. Fletcher

Beilstein J. Org. Chem. 2015, 11, 2435–2443, doi:10.3762/bjoc.11.264

• formation of C–C bonds. Here we describe the asymmetric alkylation of alkylzirconium species to racemic 3,6-dihydro-2H-pyrans. Two systems were examined: 3-chloro-3,6-dihydro-2H-pyran using linear optimization (45–93% ee, up to 33% yield, 5 examples) and 3,6-dihydro-2H-pyran-3-yl diethyl phosphate with the

• obtained by ring-closing methods [29][30]. To extend our previously reported DYKATs beyond all-carbon electrophiles we decided to examine 3-chloro-3,6-dihydro-2H-pyran (2a, Scheme 1b). This was envisaged to be a challenging substrate. The presence of oxygen in the ring would modify the electronics, and

• likely the reactivity, of the starting material. The oxygen lone pairs on 2a could potentially interact with the copper-catalyst or alkyl metal nucleophiles. Results and Discussion We first examined the in situ hydrometallation/AAA of 4-phenyl-1-butene (4) to racemic 3-chloro-3,6-dihydro-2H-pyran (2a

Recent applications of ring-rearrangement metathesis in organic synthesis

• Sambasivarao Kotha,
• Milind Meshram,
• Priti Khedkar,
• Shaibal Banerjee and
• Deepak Deodhar

Beilstein J. Org. Chem. 2015, 11, 1833–1864, doi:10.3762/bjoc.11.199

• catalyst 2 to furnish exclusively fused tricyclic systems 83a and 83b in 85% and 61% yields, respectively. Substitution on the cyclohexene system as in compound 82 did not deliver the RRM product (Scheme 16). Pyran systems Donnard and co-workers [21] have accomplished a RRM approach for assembling complex

• required building block 85 has been prepared from compound 84 by allylation with allyl bromide (37). Later, the pyran derivative 85 was treated with catalyst 2 to generate the bicyclic system 86 (73%) (Scheme 17). They also demonstrated a RCM–ROM–RCM cascade using a strain-free allyl heterocycle as useful

• neodysiherbaine via the RRM protocol. To this end, the oxabicyclo[2.2.1]hept-5-ene 256 was subjected to a RRM cascade with catalyst 2 in dichloromethane to produce pyran derivative 257 in 84% yield, which serves as a core structural unit of disyherbaine. Highly functionalized pyran derivative 259 was obtained by

Preparation of conjugated dienoates with Bestmann ylide: Towards the synthesis of zampanolide and dactylolide using a facile linchpin approach

• Jingjing Wang,
• Samuel Z. Y. Ting and
• Joanne E. Harvey

Beilstein J. Org. Chem. 2015, 11, 1815–1822, doi:10.3762/bjoc.11.197

• aldehyde fragment 6 by asymmetric alkynylation, and form the pyran using an oxa-Michael addition, in a manner reminiscent of that employed by Uenishi and co-workers [34]. Finally, macrocyclisation will be achieved through the well-established strategy of ring-closing metathesis at C8–C9. Results and

Spiro annulation of cage polycycles via Grignard reaction and ring-closing metathesis as key steps

• Sambasivarao Kotha,
• Mohammad Saifuddin,
• Rashid Ali and
• Gaddamedi Sreevani

Beilstein J. Org. Chem. 2015, 11, 1367–1372, doi:10.3762/bjoc.11.147

• product 20 (Scheme 6). Conclusion In summary, we have demonstrated a new approach to intricate C2-symmetric cage bis-spirocyclic pyran derivative 7 through an allyl Grignard reaction and an RCM sequence. The strategy demonstrated here involves an atom economic process. The synthetic sequence demonstrated

A new and efficient procedure for the synthesis of hexahydropyrimidine-fused 1,4-naphthoquinones

• Marcelo Isidoro P. Reis,
• Vinícius R. Campos,
• Jackson A. L. C. Resende,
• Fernando C. Silva and
• Vitor F. Ferreira

Beilstein J. Org. Chem. 2015, 11, 1235–1240, doi:10.3762/bjoc.11.137

• naphthoquinones (Figure 1) such as naphtho[2,3-b]furan [5][6][7][8][9][10][11][12][13][14], naphtho-pyran [15][16][17][18], benzo[f]indole [19][20][21][22][23][24], benzo[g]quinolone [25], benzo[b]carbazole [26], naphtho[2,3-b]thiophene [27][28][29][30][31][32][33] and naphtho[2,3-b]]oxazole [34] have been

Electrochemical selenium- and iodonium-initiated cyclisation of hydroxy-functionalised 1,4-dienes

• Philipp Röse,
• Steffen Emge,
• Jun-ichi Yoshida and
• Gerhard Hilt

Beilstein J. Org. Chem. 2015, 11, 174–183, doi:10.3762/bjoc.11.18

• and pyran derivatives under indirect electrochemical conditions generating selenium or iodonium cations. The reactions proceed in good yields and regioselectivities for the formation of single diastereomers. Keywords: cyclic ethers; cyclisation; 1,4-dienes; electrochemistry; iodonium; selenium

• are in turn potential substrates for the synthesis of functionalised heterocycles. Particularly, we were interested in the synthesis of tetrahydrofuran and pyran derivatives. Those heterocycles are prevalent substructures in many natural compounds, pesticides and drugs with antifungal and

• antibacterial properties [10][11][12][13]. For this purpose, we investigated a protocol for the straight forward synthesis of 1,4-dienols which should be cyclised into the corresponding tetrahydrofuran or pyran derivatives. With our sight set on efficient and atom economic organic reactions electrochemistry

Synthesis of rigid p-terphenyl-linked carbohydrate mimetics

• Maja Kandziora and
• Hans-Ulrich Reissig

Beilstein J. Org. Chem. 2014, 10, 1749–1758, doi:10.3762/bjoc.10.182

• from the side of the pyran moiety is assumed since the 1,2-oxazine side is more hindered by the bulky N-benzyl moiety. The secondary hydroxy group of 12a was protected employing t-butyldimethylsilyl trifluoromethanesulfonate and 2,6-lutidine in quantitative yield. The Lewis acid-promoted rearrangement

• spectroscopy that aminopyran 25 is not stable and slowly cyclizes to 24; after two days in CDCl3 solution approximately 20% of aminopyran 25 were converted into 24. This result indicates that the N–O bond cleavage of 12a preceded as expected, but that the produced amino group of the pyran ring seems to be in

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

C–H-Functionalization logic guides the synthesis of a carbacyclopamine analog

• Sebastian Rabe,
• Johann Moschner,
• Marina Bantzi,
• Philipp Heretsch and
• Athanassios Giannis

Beilstein J. Org. Chem. 2014, 10, 1564–1569, doi:10.3762/bjoc.10.161

• tetrahydropyranyl ether (3,4-dihydro-2H-pyran, cat. pyridinium para-toluenesulfonate, CH2Cl2, 25 °C, quantiative, inconsequential mixture of diastereoisomers), and the C17 carbonyl group was transformed into its 2-picolylimine (2-picolylamine, cat. para-toluenesulfonic acid, toluene, 111 °C, 92% yield). Subjecting

Multichromophoric sugar for fluorescence photoswitching

• Stéphane Maisonneuve,
• Rémi Métivier,
• Pei Yu,
• Keitaro Nakatani and
• Juan Xie

Beilstein J. Org. Chem. 2014, 10, 1471–1481, doi:10.3762/bjoc.10.151

• -dicyanomethylene-2-tert-butyl-6-(p-dialkylaminostyryl)-4H-pyran) [3] with a photochromic diarylethene (DAE) which showed a photoreversible two-way FRET controlled by the state of the photochromic moiety, and 49% quenching of the fluorescence upon UV irradiation [4]. Bifunctional molecules built on two distinct

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

Boron-substituted 1,3-dienes and heterodienes as key elements in multicomponent processes

• Ludovic Eberlin,
• Fabien Tripoteau,
• François Carreaux,
• Andrew Whiting and
• Bertrand Carboni

Beilstein J. Org. Chem. 2014, 10, 237–250, doi:10.3762/bjoc.10.19

• presence of Yb(fod)3 to afford 2-alkoxy-3,4-dihydro-5-vinyl-2H-pyran 33. In the presence of electron-poor dienophiles, as N-phenylmaleimide, maleic anhydride, activated azo compounds or naphthoquinone, 33 underwent normal Diels–Alder reactions thus giving the corresponding cycloadducts 34 as single

Synthesis of new enantiopure poly(hydroxy)aminooxepanes as building blocks for multivalent carbohydrate mimetics

• Léa Bouché,
• Maja Kandziora and
• Hans-Ulrich Reissig

Beilstein J. Org. Chem. 2014, 10, 213–223, doi:10.3762/bjoc.10.17

• have the drawbacks of carbohydrates such as low binding affinity or instability [4][5]. Many carbohydrates and their mimetics contain pyran rings, however, the corresponding ring-expanded compounds, oxepanes, have been investigated only in a limited number of studies. Several oxepane units can be found

Organobase-catalyzed three-component reactions for the synthesis of 4H-2-aminopyrans, condensed pyrans and polysubstituted benzenes

• Moustafa Sherief Moustafa,
• Saleh Mohammed Al-Mousawi,
• Maghraby Ali Selim,
• Ahmed Mohamed Mosallam and
• Mohamed Hilmy Elnagdi

Beilstein J. Org. Chem. 2014, 10, 141–149, doi:10.3762/bjoc.10.11

• , P.O. Box 83523, Qena, Egypt 10.3762/bjoc.10.11 Abstract Novel routes for the preparation of 2-amino-4H-pyran-3-carbonitrile 9, amino-arylbenzoic acid ester derivatives 13a,b, 2-aminotetrahydro-4H-chromene-3-carbonitrile 18, 3-amino-4-cyanotetrahydronaphthalene-2-carboxylic acid ester 26 and 4-amino

• -pyran 9 and that the yield of the process can be improved if equimolar amounts of DMADC, benzylidenemalononitrile and malononitrile are used [20]. Similar observations have been made in previous studies of these reactions using 1-methylimidazole [21]. Recently we observed that 2-amino-4H-pyran 9 can be

• generate 10 that cyclizes to form 12. Subsequent aromatization of 12 produces the benzoate derivative 13b. Alternatively, 8 could react with malononitrile to yield 11 that then serve as a precursor to 13 (Scheme 4). In support of the former mechanistic proposal, it was observed that 2-amino-4H-pyran 9

Synthesis of five- and six-membered cyclic organic peroxides: Key transformations into peroxide ring-retaining products

• Alexander O. Terent'ev,
• Dmitry A. Borisov,
• Vera A. Vil’ and
• Valery M. Dembitsky

Beilstein J. Org. Chem. 2014, 10, 34–114, doi:10.3762/bjoc.10.6