Surprisingly facile CO₂ insertion into cobalt alkoxide bonds: A theoretical investigation

• Willem K. Offermans,
• Claudia Bizzarri,
• Walter Leitner and
• Thomas E. Müller

Beilstein J. Org. Chem. 2015, 11, 1340–1351, doi:10.3762/bjoc.11.144

• theoretical study, in which the initiation and propagation steps of the copolymerisation were addressed. The initiation started with the coordination of epoxide at a penta-coordinated metal–salen complex, followed by a nucleophilic, SN2-like, back-side attack on such a coordinated epoxide. The propagation

• comprised a syn-insertion of CO2 into the metal–alkoxide bond and a bimolecular chain transfer of a metal-bound, carbonate-terminated, growing chain to a metal-coordinated and, thus, activated epoxide (see Scheme 2). For hepta-coordinated Cr(III)– and Al(III)–salen complexes, the CO2 insertion requires

• applied to atoms directly involved or in close vicinity of the reaction center, but involves less demanding calculations for the outer periphery. Though kinetically favoured, the insertion of CO2 into the zinc–alkoxide bond turned out to be thermodynamically less favourable than the insertion of epoxide

Selected synthetic strategies to cyclophanes

• Sambasivarao Kotha,
• Mukesh E. Shirbhate and
• Gopalkrushna T. Waghule

Beilstein J. Org. Chem. 2015, 11, 1274–1331, doi:10.3762/bjoc.11.142

• 339 (22%). Treatment of 339 with 1 equiv of m-chloroperbenzoic acid gave the epoxide 340 (80%), followed by HCl treatment gave [8]paracyclophane 341 (93%) (Scheme 59). Synthesis of the macrocyclic portion of longithorone C (DA reaction): In 1994 longithorone A was first described by Schmitz and co

The chemical behavior of terminally tert-butylated polyolefins

• Dagmar Klein,
• Henning Hopf,
• Peter G. Jones,
• Ina Dix and
• Ralf Hänel

Beilstein J. Org. Chem. 2015, 11, 1246–1258, doi:10.3762/bjoc.11.139

• yielded the symmetrical epoxide 32 with DMDO. Analogously, 19 was converted to mono-epoxide 33 with MCPBA and to 34 with DMDO. Diels–Alder addition of 7 with N-phenyltriazolinedione (PTAD) did not take place. Extension of the conjugated π-system to the next higher vinylog, 19, caused NPTD-addition to the

• -chloroperbenzoic acid (MCPBA) in chloroform at room temperature overnight. Surprisingly, it was neither the mono- epoxide 29 nor its non-terminal isomer 32 but the ketone 31 that was obtained in low yield (ca. 25%). The structure follows from the spectroscopic data (see Supporting Information File 1); the carbonyl

• group is readily seen in the IR spectrum (νmax = 1702 cm−1) and the carbonyl carbon signal in the 13C NMR spectrum at δ = 217 ppm is also of particular diagnostic value. We propose that 31 is produced from epoxide 29 by initial protonation to the oxonium ion 30, which then undergoes a Wagner–Meerwein

Synthesis of a hexasaccharide partial sequence of hyaluronan for click chemistry and more

• Marina Bantzi,
• Stephan Rigol and
• Athanassios Giannis

Beilstein J. Org. Chem. 2015, 11, 604–607, doi:10.3762/bjoc.11.67

• double bond with Murray's reagent [29][30] yielded the analogous epoxide that was treated with NaN3 in order to afford the desired azido-modified hexasaccharide 10. Conclusion In conclusion, hexasaccharide 10 was successfully prepared in 26 steps and is readily equipped with a terminal azido group. Thus

Synthesis and surface grafting of a β-cyclodextrin dimer facilitating cooperative inclusion of 2,6-ANS

• Lars W. Städe,
• Thorbjørn T. Nielsen,
• Laurent Duroux,
• Reinhard Wimmer,
• Kyoko Shimizu and
• Kim L. Larsen

Beilstein J. Org. Chem. 2015, 11, 514–523, doi:10.3762/bjoc.11.58

• ) and subsequent ring opening of the epoxide by sodium azide in PEG400 (Scheme 2). In addition to surface grafting of the β-CD dimer, an azide-functionalized quartz slide was grafted with propargyl alcohol (PA, not shown), by CuAACas well, in order to probe changes in 2,6-ANS fluorescence related to

Electrochemical oxidation of cholesterol

• Jacek W. Morzycki and
• Andrzej Sobkowiak

Beilstein J. Org. Chem. 2015, 11, 392–402, doi:10.3762/bjoc.11.45

• %), along with the 7-oxo product 9a (15–19%). In addition to these products, epoxide 10a (1.5–3%) was also formed under constant current conditions (Scheme 3). Irrespective of the iron complex used, the reactions afforded the 7α-hydroxylated product 7a in a large excess. The authors postulated the formation

• platinum plates. The electrolysis was performed in the presence of FeCl3 and hematoporphyrin (HMP), and dioxygen was constantly delivered to the cell. Three products, 5α,6β-dichlorocholestan-3β-ol (11), 6α-chlorocholestane-3β,5ß-diol (12), and epoxide (10), as a 1:3 mixture of α and β-isomers, were

• compounds 11 (20%) and 12 (43%) were formed. Second, during the reaction with hydrogen peroxide as an oxidant under non-electrochemical conditions no products were detected, which indicates that the role of dioxygen is not the source of electrochemically generated H2O2. Furthermore, the epoxide 10 was not

Attempts to prepare an all-carbon indigoid system

• Şeref Yildizhan,
• Henning Hopf and
• Peter G. Jones

Beilstein J. Org. Chem. 2015, 11, 363–372, doi:10.3762/bjoc.11.42

• . Results and Discussion Our first attempt to prepare hydrocarbon 4 started from indene (6, Scheme 2). Epoxidation with m-chloroperbenzoic acid (MCPBA) according to a literature method [15] yielded the epoxide 7 in meager yields (Scheme 2). The methylation of 7 to 8 was achieved by the treatment with

Switching the reaction pathways of electrochemically generated β-haloalkoxysulfonium ions – synthesis of halohydrins and epoxides

• Akihiro Shimizu,
• Ryutaro Hayashi,
• Yosuke Ashikari,
• Toshiki Nokami and
• Jun-ichi Yoshida

Beilstein J. Org. Chem. 2015, 11, 242–248, doi:10.3762/bjoc.11.27

• , which is consistent with the results reported previously [22]. Treatment of 3a-Br with NaOMe resulted in a different product, namely epoxide 6a in 95% yield. In this case, the methoxide ion attacks the sulfur atom and cleaves the S–O bond under formation of an alkoxide ion. The latter intramolecularly

• attacks the carbon atom bearing the bromine substituent to give epoxide 6a (Scheme 2). Presumably, the protonation of the alkoxide ion with MeOH is slower than the intramolecular nucleophilic attack. We could not exclude the possibility that a protonated DMSO molecule presumably generated by the reaction

• mechanism involving the back-side attack of the alkoxide ion to form epoxide 6a. Reactions of β-iodoalkoxysulfonium ions generated from (Z)-5-decene We next examined the reactions of β-iodoalkoxysulfonium ion 3a-I generated by the reaction of (Z)-5-decene (2a) with I+/DMSO (1-I) cation pool [22] (Scheme 1

Anion effect controlling the selectivity in the zinc-catalysed copolymerisation of CO₂ and cyclohexene oxide

• Sait Elmas,
• Muhammad Afzal Subhani,
• Walter Leitner and
• Thomas E. Müller

Beilstein J. Org. Chem. 2015, 11, 42–49, doi:10.3762/bjoc.11.7

• with epoxides (Scheme 1) is a prime example of a particularly attractive transformation of CO2 [8][9] and is at the verge of commercialisation [8]. In this transformation, the low energy level of the CO2 molecule is overcome by reacting CO2 with an epoxide as energy-rich comonomer [10]. Homogeneous and

• spectra (Figure 2) revealed a profile of epoxide consumption consistent with a first order reaction in both CO2 and epoxide. The initial rate for the consumption of CHO was 5.03 molCHO.(molcat.h)−1. Ether and carbonate linkages in the polyethercarbonate product were formed in parallel in a ratio of 9.8

• the zinc centres. Insertion of CO2 into the metal–alcoholate bond provides a coordinated carbonate species [15]. An epoxide molecule coordinates to a neighbouring zinc centre and the nucleophilic attack by the neighbouring carbonate species leads to chain growth. Insertion of the next CO2 molecule

A carbohydrate approach for the formal total synthesis of (−)-aspergillide C

• Pabbaraja Srihari,
• Namballa Hari Krishna,
• Ydhyam Sridhar and
• Ahmed Kamal

Beilstein J. Org. Chem. 2014, 10, 3122–3126, doi:10.3762/bjoc.10.329

• reaction followed by the reduction of the triple bond to the trans double bond. Alkyne 7 can be synthesized from alkyne 8 involving an isomerization reaction. Alkyne 8 was easily accessible from (R)-propylene oxide (9) through an epoxide opening reaction with 1-butyne. Results and Discussion In recent work

• on aspergillides, Achmatowicz adducts were utilized as the key source for the construction of the dihydropyran moiety and the side arm was synthesized using a Zipper rearrangement as a key reaction after an epoxide ring opening reaction of (R)-propylene oxide/(S)-propylene oxide with n-BuLi. In the

First chemoenzymatic stereodivergent synthesis of both enantiomers of promethazine and ethopropazine

• Paweł Borowiecki,
• Daniel Paprocki and
• Maciej Dranka

Beilstein J. Org. Chem. 2014, 10, 3038–3055, doi:10.3762/bjoc.10.322

• [tetrabutylammonium bromide (TBAB) or tetrabutylammonium hydrogensulfate (TBAHS)], the epoxide 2 ring opening proceeded unsuccessfully. Again, the amount of the formed impurities was too large to isolate pure fraction. This provoked us to change the synthetic strategy by excluding at first propylene oxide (2) as the

Thermal and oxidative stability of the Ocimum basilicum L. essential oil/β-cyclodextrin supramolecular system

• Daniel I. Hădărugă,
• Nicoleta G. Hădărugă,
• Corina I. Costescu,
• Ioan David and
• Alexandra T. Gruia

Beilstein J. Org. Chem. 2014, 10, 2809–2820, doi:10.3762/bjoc.10.298

• the raw O. basilicum L. essential oil. This feature can be observed for the relative concentrations in the complex with an increase of 81% for linalool epoxide (3), 43% for caryophyllene epoxide (17), 52% for aristolene epoxide (21) and 61.5% for aromadendrene epoxide (23) (Table 1). The

• raw sample). Some of sesquiterpene oxides found in the raw essential oil exhibited a slow decrease in the relative concentrations in the degraded samples (e.g., caryophyllene oxide (17) and aristolene epoxide (21)). This behavior suggests that the sesquiterpenes are more susceptible to degradation

• % to 0.84% (a decrease of almost 23%) and α-bulnesene (14) with a decrease of only 1.1% (Table 3). The degradation compounds from the sesquiterpene epoxide class were found in very low relative concentrations in the recovered O. basilicum L. essential oil from the non-degraded or degraded β-CD complex

Regio- and stereoselective synthesis of new diaminocyclopentanols

• Evgeni A. Larin,
• Valeri S. Kochubei and
• Yuri M. Atroshchenko

Beilstein J. Org. Chem. 2014, 10, 2513–2520, doi:10.3762/bjoc.10.262

• .10.262 Abstract The optimal conditions for regio- and stereoselective epoxide ring opening of N,N-disubstituted 1,2-epoxy-3-aminocyclopentanes by different nucleophilic reagents have been developed. The substituents on the nitrogen atom in the epoxide precursor and the orientation of the oxirane ring are

• aminolysis of epoxides 6a,b afforded mainly C1 adducts 13a,b arising from trans-diaxal opening of the epoxide ring. Using a Lewis acid catalyst, epoxides 6a,b were transformed into diaminocyclopentanols 14a,b via an alternative pathway involving the formation of aziridinium intermediate 17. Keywords

• of stereoselective epoxide opening of these cyclic amine derivatives are limited to the preparation of the corresponding diols under acidic conditions [23]. Other reported strategies involve the formation of diaminocyclohexanols from epoxides under basic conditions [24] or by activating the epoxides

New highlights of the syntheses of pyrrolo[1,2-a]quinoxalin-4-ones

• Emilian Georgescu,
• Alina Nicolescu,
• Florentina Georgescu,
• Florina Teodorescu,
• Daniela Marinescu,
• Ana-Maria Macsim and
• Calin Deleanu

Beilstein J. Org. Chem. 2014, 10, 2377–2387, doi:10.3762/bjoc.10.248

• towards N-bridged heterocyclic compounds [17][18][19][20] prompted us to investigate the one-pot three-component reactions of various substituted benzimidazoles with alkyl bromoacetates and electron-deficient alkynes in presence of an epoxide. Herein, we report a simple one-pot three-component synthetic

Indium-mediated allylation in carbohydrate synthesis: A short and efficient approach towards higher 2-acetamido-2-deoxy sugars

• Christopher Albler,
• Ralph Hollaus,
• Hanspeter Kählig and
• Walther Schmid

Beilstein J. Org. Chem. 2014, 10, 2230–2234, doi:10.3762/bjoc.10.231

• (CHCO2Me)) generated allylic epoxides 4a–c, which in turn permitted the application of reliable palladium chemistry for the epoxide opening [27][28][29]. Thus, compounds 4a–c were regio- and stereoselectively opened with trimethylsilyl azide and Pd(PPh3)4 as a catalyst [30], furnishing syn-azido alcohols

De novo macrolide–glycolipid macrolactone hybrids: Synthesis, structure and antibiotic activity of carbohydrate-fused macrocycles

• Richard T. Desmond,
• Anniefer N. Magpusao,
• Chris Lorenc,
• Jeremy B. Alverson,
• Nigel Priestley and
• Mark W. Peczuh

Beilstein J. Org. Chem. 2014, 10, 2215–2221, doi:10.3762/bjoc.10.229

• , stereogenic centers and stereoelectronic effects combine to dictate the “topology” or overall fold of a macrocycle. The structure of β-D-galactose-[13]-macrodiolide 3 [9], derived from X-ray data, originated this line of investigation. It showed that both esters and the epoxide unit are each composed of four

• coplanar atoms that significantly reduce the number of freely rotatable bonds in the molecule [9][10][12][23][24][25] and rigidify its structure. The consequence is that the esters, alkene and epoxide units are not coplanar, but are set at angles to each other (Figure 2 ). The result is a twist in the

Palladium-catalysed cyclisation of alkenols: Synthesis of oxaheterocycles as core intermediates of natural compounds

• Miroslav Palík,
• Jozef Kožíšek,
• Peter Koóš and
• Tibor Gracza

Beilstein J. Org. Chem. 2014, 10, 2077–2086, doi:10.3762/bjoc.10.216

• dichloromethane and subsequent acidic epoxide hydrolysis produced the syn-diol rac-39. The following protection of diol rac-39 as its acetonide and the primary hydroxy group deprotection using sodium methoxide afforded alcohol rac-40 in good yield (43% over 5 steps). Next, Swern oxidation of the primary hydroxy

Application of cyclic phosphonamide reagents in the total synthesis of natural products and biologically active molecules

• Thilo Focken and
• Stephen Hanessian

Beilstein J. Org. Chem. 2014, 10, 1848–1877, doi:10.3762/bjoc.10.195

• chiral auxiliary through ozonolysis followed by protection of the side chain as TBDPS ether afforded cyclopentanone 155. Saegusa–Ito oxidation followed by epoxidation of the formed enone gave 156 as the major isomer (dr 9:1). Regioselective reductive opening of the epoxide with Na[PhSeB(OEt)3] produced

• oxa-Pictet–Spengler reaction from 2,6-dihydroxybenzoic acid 173 and ketal aldehyde 174 as key building blocks (Figure 10). The 2,6-dihydroxybenzoic acid 173 is accessible by opening of epoxide 175 as chiron with a suitable nucleophile. The ketal aldehyde 174 would be derived from butenolide 176

Comparing kinetic profiles between bifunctional and binary type of Zn(salen)-based catalysts for organic carbonate formation

• Carmen Martín and
• Arjan W. Kleij

Beilstein J. Org. Chem. 2014, 10, 1817–1825, doi:10.3762/bjoc.10.191

• [salphen = N,N’-phenylene-1,2-bis[salicylidene]imine] (Figure 1, 1) combined with a nucleophilic ammonium halide salt [26][27], or an analogous bifunctional system (Figure 1, 2) containing a Lewis acidic and nucleophilic center within the same molecule [29]. Mechanistic investigations for these CO2/epoxide

• NBu3 able to activate CO2 whereas the other molecule helps to ring-open a coordinated epoxide. This activation mode differs from one reported for the binary system based on Al complex 3/NBu4I (Figure 1) [37] and the first-order dependence with respect to each catalyst and co-catalyst displayed when the

• are the efforts from Coates and co-workers [44] and the kinetic studies described by the group of Williams [45]. In each of these latter cases a binuclear mechanism was proposed for the copolymerization reaction of CO2 and epoxide, establishing a second-order dependence for mononuclear Zn complex 7

Copolymerization and terpolymerization of carbon dioxide/propylene oxide/phthalic anhydride using a (salen)Co(III) complex tethering four quaternary ammonium salts

• Jong Yeob Jeon,
• Seong Chan Eo,
• Jobi Kodiyan Varghese and
• Bun Yeoul Lee

Beilstein J. Org. Chem. 2014, 10, 1787–1795, doi:10.3762/bjoc.10.187

• /epoxide copolymerizations, shows high activity for propylene oxide/phthalic anhydride (PO/PA) copolymerizations and PO/CO2/PA terpolymerizations. In the PO/PA copolymerizations, full conversion of PA was achieved within 5 h, and strictly alternating copolymers of poly(1,2-propylene phthalate)s were

Rasta resin–triphenylphosphine oxides and their use as recyclable heterogeneous reagent precursors in halogenation reactions

• Xuanshu Xia and
• Patrick H. Toy

Beilstein J. Org. Chem. 2014, 10, 1397–1405, doi:10.3762/bjoc.10.143

• alcohol, aziridine, aldehyde and epoxide halogenation reactions from which the desired products are easily isolated and the phosphine oxide byproduct is readily recycled. Results and Discussion Rasta resin 16 was prepared by oxidation of 14, which was prepared as previously reported [28], using H2O2

• the reaction mixture was washed and dried, and then used directly for the next reaction cycle. Excellent yields were successfully obtained for 8 runs with both 4H and 8B. Gel-phase 31P NMR analysis of 16 recovered at the end of these experiments indicated no change in its oxidation state. Epoxide

• halogenation reactions With the versatility and excellent reactivity of 16 established, we were encouraged to examine our method in the epoxide halogenation reactions shown in Scheme 2. Since these reactions require the use of a base, we designed a bifunctional rasta resin, RR-NBniPr2-PPh3=O 18 (Scheme 5

An economical and safe procedure to synthesize 2-hydroxy-4-pentynoic acid: A precursor towards ‘clickable’ biodegradable polylactide

• Quanxuan Zhang,
• Hong Ren and
• Gregory L. Baker

Beilstein J. Org. Chem. 2014, 10, 1365–1371, doi:10.3762/bjoc.10.139

• sublimated under vacuum to give 24.1 g of acid 1 in 49.0% yield [17]. 1H NMR (500 MHz, CDCl3) δ 4.35 (t, J = 4.5 Hz, 1H), 2.68 (m, 2H), 2.08 (t, J = 2.5 Hz, 1H); 13C NMR (125 MHz, CDCl3) δ 177.5, 77.7, 71.9, 68.5, 24.4. Synthesis of 2-hydroxy-4-pentynoic acid (1). Synthesis of 1 via epoxide ring opening with

Molecular recognition of surface-immobilized carbohydrates by a synthetic lectin

• Melanie Rauschenberg,
• Eva-Corrina Fritz,
• Christian Schulz,
• Tobias Kaufmann and
• Bart Jan Ravoo

Beilstein J. Org. Chem. 2014, 10, 1354–1364, doi:10.3762/bjoc.10.138

• microcontact printed on epoxide-terminated self-assembled monolayers. Successive prints resulted in simple microarrays of two carbohydrates. The selectivity of the synthetic lectin was investigated by incubation on the immobilized carbohydrates. Selective binding of the synthetic lectin to immobilized NANA and

• HisHis towards immobilized NANA in comparison with the glycosides of glucose (Glc), galactose (Gal) and mannose (Man) (Figure 1). In this study, we exploit the epoxide ring opening reaction of amine-tethered carbohydrates on epoxide-terminated SAMs [42] to print carbohydrate microarrays on silicon and

• glass substrates. Epoxide-terminated SAMs are particularly versatile for the fabrication of biological arrays [43][44] and we have recently demonstrated that epoxide-terminated substrates are easily modified using µCP [45]. The incubation of the synthetic lectin FITC-HisHis as well as two natural

Selective allylic hydroxylation of acyclic terpenoids by CYP154E1 from Thermobifida fusca YX

• Anna M. Bogazkaya,
• Clemens J. von Bühler,
• Sebastian Kriening,
• Alexandrine Busch,
• Alexander Seifert,
• Jürgen Pleiss,
• Sabine Laschat and
• Vlada B. Urlacher

Beilstein J. Org. Chem. 2014, 10, 1347–1353, doi:10.3762/bjoc.10.137

• converted only up to 4% to get a mixture of 2,3-epoxynerol (6) and diepoxynerol (8) at a ratio of 58:42. V286A and V286F catalysed the oxidation of geraniol (1) to a mixture of epoxides 5 and 7 as in the case of V286L. Two epoxide products appeared at a ratio of 59:41 (V286A), and only 6% substrate

• -hydroxygeranylacetone (11, 8%) and the epoxide 9,10-epoxygeranylacetone (17, 9%). Similar to the conversion of geraniol (1), the regio- and chemoselectivity of geranylacetone oxidation catalysed by the mutants was different compared to the wild type enzyme. The product analysis revealed a strong preference of all three

• mutants for the formation of C7-hydroxylated compound 11 as the main product. Variant V286L produced 44% of 7-hydroxygeranylactone (11) as well as the compounds 13 (18%) and 15 (35%). Substrate epoxidation leading to the epoxide 17 was much slower compared to the wild type: this product accounted to less

Heronapyrrole D: A case of co-inspiration of natural product biosynthesis, total synthesis and biodiscovery

• Jens Schmidt,
• Zeinab Khalil,
• Robert J. Capon and
• Christian B. W. Stark

Beilstein J. Org. Chem. 2014, 10, 1228–1232, doi:10.3762/bjoc.10.121

• effect an epoxidation of 8. Application of substoichiometric amounts of oxidant (Oxone®) delivered the isomeric mono-epoxides 9 and 10 as the main constituents, along with minor amounts of the bis-epoxide 11. Of note, on work-up 9 was observed to undergo partial cyclization to the desired tetrahydrofuran