Robust perfluorophenylboronic acid-catalyzed stereoselective synthesis of 2,3-unsaturated O-, C-, N- and S-linked glycosides

• Madhu Babu Tatina,
• Xia Mengxin,
• Rao Peilin and
• Zaher M. A. Judeh

Beilstein J. Org. Chem. 2019, 15, 1275–1280, doi:10.3762/bjoc.15.125

• activation of alcohols [24], epoxide opening [25][26], Friedel–Crafts alkylations [27], dehydrative glycosylation [28] and many other reactions [29][30][31]. The robustness and mildness of organoboronic acid catalysts in comparison to traditional strong Lewis and Brønsted acid catalysts inspired us to

Phylogenomic analyses and distribution of terpene synthases among Streptomyces

• Lara Martín-Sánchez,
• Kumar Saurabh Singh,
• Mariana Avalos,
• Gilles P. van Wezel,
• Jeroen S. Dickschat and
• Paolina Garbeva

Beilstein J. Org. Chem. 2019, 15, 1181–1193, doi:10.3762/bjoc.15.115

• enantiomers of the corresponding alcohols (R)- and (S)-albaflavenol (16ab) and the epoxide 4β,5β-epoxy-2-epi-zizaan-6β-ol (18) are known oxidation products that are all made by a cytochrome P450 monooxygenase [10][29] that is genetically clustered with the epi-isozizaene synthase for the cyclisation of FPP to

Synthesis of acylglycerol derivatives by mechanochemistry

• Karen J. Ardila-Fierro,
• Andrij Pich,
• Marc Spehr,
• José G. Hernández and
• Carsten Bolm

Beilstein J. Org. Chem. 2019, 15, 811–817, doi:10.3762/bjoc.15.78

• by epoxide ring-opening and esterification reactions with fatty acids 3 (Scheme 1). If successful, developing a multistep approach to prepare DAGs would contribute to the expansion of synthetic mechanochemical methodologies in ball mills [28][29][30][31], which are often limited to single-step

• hands, a selective epoxide ring-opening reaction with fatty acids 3 leading to the formation of the corresponding sn-1,3-protected monoacylglycerols (MAGs 4) was attempted (Scheme 3). Initially, commonly used solution-based protocols were tested in the ball mill [33]. For example, 2 was reacted with

• catalysts such as iron(III) chloride or bismuth(III) triflate was reported. However, the implementation of these protocols in the ball mill only led to trace amounts (less than 5% yield) of the protected monoacylglycerol 4a. Finally, one of the well-established Jacobsen catalysts for the epoxide ring

New sesquiterpenoids from the South China Sea soft corals Clavularia viridis and Lemnalia flava

• Qihao Wu,
• Yuan Gao,
• Meng-Meng Zhang,
• Li Sheng,
• Jia Li,
• Xu-Wen Li,
• Hong Wang and
• Yue-Wei Guo

Beilstein J. Org. Chem. 2019, 15, 695–702, doi:10.3762/bjoc.15.64

• known compounds were readily identified as cupalaurenol (5) [13], 1-hydroxyalloaromadendrene (7) [14], and humulene epoxide II (8) [15] by comparing their NMR spectroscopic data and optical rotation with those reported in the literature. Isobromolaurenisol (1) was obtained as an optically active

Oxidative radical ring-opening/cyclization of cyclopropane derivatives

• Yu Liu,
• Qiao-Lin Wang,
• Zan Chen,
• Cong-Shan Zhou,
• Bi-Quan Xiong,
• Pan-Liang Zhang,
• Chang-An Yang and
• Quan Zhou

Beilstein J. Org. Chem. 2019, 15, 256–278, doi:10.3762/bjoc.15.23

• naphthaldehyde 33 was obtained in 61% yield (Scheme 9, reaction b). Furthermore, the product 31a could also be transformed to the CF3-substituted epoxide 34 in the presence of 2 equiv m-CPBA (m-chloroperbenzoic acid) (Scheme 9, reaction c). A radical-trapping experiment was conducted with the addition of TEMPO

• aerobic oxidation of easily available cyclopropanols 91 via intermediate formation of peroxyketone intermediates 145, followed by enantioselective epoxide formation in the presence of a poly-L-leucine catalyst and DBU (Scheme 40) [120]. In 2014, a practical method for the conversion of 1,2-disubstituted

Synthesis of nonracemic hydroxyglutamic acids

• Dorota G. Piotrowska,
• Iwona E. Głowacka,
• Andrzej E. Wróblewski and
• Liwia Lubowiecka

Beilstein J. Org. Chem. 2019, 15, 236–255, doi:10.3762/bjoc.15.22

• acid Cleavage of the 5-membered ring in the protected epoxide 88 obtained from (S)-pyroglutamic acid [93][94][95] gave the methyl ester 89 which, when adsorbed on silica gel, smoothly underwent stereospecific epoxide ring opening to give the oxazolidinone 90 (Scheme 23) [96]. Before installation of the

Organometallic vs organic photoredox catalysts for photocuring reactions in the visible region

• Aude-Héloise Bonardi,
• Frédéric Dumur,
• Guillaume Noirbent,
• Jacques Lalevée and
• Didier Gigmes

Beilstein J. Org. Chem. 2018, 14, 3025–3046, doi:10.3762/bjoc.14.282

• photoreticulation processes of multifunctional radical (acrylate, methacrylate…) or cationic (epoxide) monomers. Undoubtedly, the advantage of the photoredox catalysis approach is the high efficiency of the system to initiate the polymerization upon mild light irradiation conditions (as the catalyst is regenerated

Copolymerization of epoxides with cyclic anhydrides catalyzed by dinuclear cobalt complexes

• Yo Hiranoi and
• Koji Nakano

Beilstein J. Org. Chem. 2018, 14, 2779–2788, doi:10.3762/bjoc.14.255

• epoxide/CA copolymerization was constricted until recently because of low catalytic activity and poor control over the main chain sequence (formation of ether linkages through consecutive epoxide enchainment) and molecular weight. In 2007, Coates and co-workers reported that β-diiminate zinc complexes

• exhibited a high catalytic activity for the epoxide/CA copolymerization [14]. The resulting polyesters were found to possess completely alternating structures with high molecular weight and relatively narrow polydispersity. Following this report, a range of highly active and/or selective catalysts has been

• methods [22][23][24][25][26]. Cooperative dinuclear metal catalysts have been considered as a promising design for high activity and/or selectivity in organic transformations including polymerizations [27][28][29][30]. This was found to be true for the epoxide/CA copolymerization. In 2013, Lu and co

Pathoblockers or antivirulence drugs as a new option for the treatment of bacterial infections

• Matthew B. Calvert,
• Varsha R. Jumde and
• Alexander Titz

Beilstein J. Org. Chem. 2018, 14, 2607–2617, doi:10.3762/bjoc.14.239

• of LecA with its electrophilic epoxide warhead [40]. It could be demonstrated that 11 is a covalent lectin inhibitor, which provided the first proof-of-concept for this new approach to lectin inhibition. To date, the most potent LecA inhibitor 12 has been designed by the Pieters group, where two

Synergistic approach to polycycles through Suzuki–Miyaura cross coupling and metathesis as key steps

• Sambasivarao Kotha,
• Milind Meshram and
• Chandravathi Chakkapalli

Beilstein J. Org. Chem. 2018, 14, 2468–2481, doi:10.3762/bjoc.14.223

• the corresponding epoxide 110. Unfortunately, generation of epoxide was not realized (Scheme 16). Macrocycles To develop new synthetic strategies to various cyclophanes, we conceived a sequential usage of the SM coupling and RCM as key steps [48][49]. In this context, the required dialdehyde 113 (80

One-pot synthesis of epoxides from benzyl alcohols and aldehydes

• Edwin Alfonzo,
• Jesse W. L. Mendoza and
• Aaron B. Beeler

Beilstein J. Org. Chem. 2018, 14, 2308–2312, doi:10.3762/bjoc.14.205

• alcohols and aldehydes. Keywords: Corey–Chaykovsky; epoxide; heterocycle; one-pot; ylide; Introduction Epoxides have historically served as strategic functional groups in target-oriented synthesis [1][2][3][4]. Common examples of their utility include stereospecific ring opening [5][6][7], rearrangements

• (NaH) was the only base that successfully afforded the desired epoxide 3, typically in excellent and reproducible yields (other bases screened included KOt-Bu, LiHMDS, TBD [25], and KOH). Furthermore, diluting the reaction after formation of the sulfonium salt, and cooling it in an ice bath, proved

• at the betaine intermediate prior to epoxide formation through displacement of THT. This is supported by example 9 which contained a para-methoxy group at the aldehyde component but was isolated as a single diastereomer [28]. Functional groups that are not compatible with this method include phenols

Studies towards the synthesis of hyperireflexolide A

• G. Hari Mangeswara Rao

Beilstein J. Org. Chem. 2018, 14, 2106–2111, doi:10.3762/bjoc.14.185

• 5 could not only act as a surrogate for C-9 carbonyl but also facilitate installation of an angular methyl group. The retrosynthetic analysis for hyperireflexolide A is depicted in Scheme 1. We envisioned that hyperireflexolide A (1) could be synthesized by metal-catalyzed opening of the epoxide 2

• of the proposed synthetic sequence. Future studies will include the stereoselective epoxidation of 11 followed by opening of the epoxide and lactonization or 1,4-nucleophilic addition to the α,β-unsaturated ketone 11 followed by epoxidation of the resulted enolate with subsequent lactonization to

Functionalization of graphene: does the organic chemistry matter?

• Artur Kasprzak,
• Agnieszka Zuchowska and
• Magdalena Poplawska

Beilstein J. Org. Chem. 2018, 14, 2018–2026, doi:10.3762/bjoc.14.177

• (RGO) have most commonly been investigated in terms of creating novel functional materials. GO is a product of oxidative exfoliation from bulk graphite [4]. GO’s structure (Figure 1a) comprises a large number of oxygen functionalities, including carboxyl (COOH), hydroxy (OH) and epoxide (see the

• alcohol. This leads to the formation of the desired ester bond (Figure 3, step e). DMAP acts both as a nucleophile and an acyl transfer reagent and suppresses the side reactions. The structure of GO includes a number of epoxide moieties, which are also reactive toward the nucleophilic reagents. The

• , (c) reaction with DMAP, (d and e) desired reaction pathway (ester or amide bond formation), (d and f) reaction of the activated carboxyl group with water molecules. Mechanism of the epoxide ring opening reaction with the GO/RGO. Generation of the free amine (nucleophile) from the corresponding amine

β-Hydroxy sulfides and their syntheses

• Mokgethwa B. Marakalala,
• Edwin M. Mmutlane and
• Henok H. Kinfe

Beilstein J. Org. Chem. 2018, 14, 1668–1692, doi:10.3762/bjoc.14.143

• ; epoxide thiolysis; β-hydroxy sulfides; sulfur-containing natural products; Review 1. Introduction Organosulfur compounds are widely distributed in nature, with marine organisms being the richest sources of these, since sulfur, as the sulfate ion, is the second most abundant anion in sea water after

• . Regioselective epoxide ring opening and 1,2-difunctionalization of alkenes are the commonly employed routes in the synthesis of such compounds. Both strategies are discussed below. 3.1 Synthesis of β-hydroxy sulfides via regioselective ring opening of epoxides The considerable ring strain present in epoxides

• thiols to give various β-hydroxy sulfides in good yields (Scheme 1) [20]. Both aryl and alkylthiols were found to be capable of opening the epoxide ring under the reaction conditions, and with respect to the epoxides, cycloalkane, alkene and 1-substituted alkene oxides were all amenable to the reaction

Glycosylation reactions mediated by hypervalent iodine: application to the synthesis of nucleosides and carbohydrates

• Yuichi Yoshimura,
• Hideaki Wakamatsu,
• Yoshihiro Natori,
• Yukako Saito and
• Noriaki Minakawa

Beilstein J. Org. Chem. 2018, 14, 1595–1618, doi:10.3762/bjoc.14.137

• , the PMB-protected epoxide 121 was converted to diene 122. The dihydropyran ring of 123 was constructed by RCM of 122 catalyzed by a Grubbs 1st generation catalyst. The isomerization of the double bond in 123 by treatment with a Wilkinson catalyst under basic conditions afforded glycal 124 (Scheme 16

Recent applications of chiral calixarenes in asymmetric catalysis

• Mustafa Durmaz,
• Erkan Halay and
• Selahattin Bozkurt

Beilstein J. Org. Chem. 2018, 14, 1389–1412, doi:10.3762/bjoc.14.117

• reaction in the following order: phase-transfer catalysis, Henry reaction, Suzuki–Miyaura cross-coupling and Tsuji–Trost allylic substitution, hydrogenation, Michael addition, aldol and multicomponent Biginelli reactions, epoxidation, Meerwein−Ponndorf−Verley reduction, aza-Diels−Alder and epoxide ring

• exhibited the best result. Aza-Diels–Alder and epoxide ring-opening reaction Manoury et al. have very recently reported facile synthesis of an enantiomerically pure inherently chiral calix[4]arene phosphonic acid (cR,pR)-121 from the readily available (cS)-enantiomer of calix[4]arene acetic acid 119 or its

• important transformations: phase-transfer catalysis, Henry reaction, Suzuki–Miyaura cross-coupling and Tsuji–Trost allylic substitution, hydrogenation, Michael addition, aldol and multicomponent Biginelli reactions, epoxidation, Meerwein–Ponndorf–Verley reduction, aza-Diels–Alder and epoxide ring-opening

Novel unit B cryptophycin analogues as payloads for targeted therapy

• Eduard Figueras,
• Adina Borbély,
• Mohamed Ismail,
• Marcel Frese and
• Norbert Sewald

Beilstein J. Org. Chem. 2018, 14, 1281–1286, doi:10.3762/bjoc.14.109

• pseudo-high-dilution conditions to afford 20 and 21 as described previously [16]. Then the diol was transformed into the epoxide following a three-step one-pot reaction as extensively used in the synthesis of cryptophycin analogues [46]. Cryptophycin analogues 22 and 23 were obtained in good purity after

• magenta. Docking of 22 to the vinca domain of β-tubulin. Surface and backbone of β-tubulin are shown in blue, GDP in yellow. No hydrogen bond formation was detected. The orientation of the azidoethoxy-ethoxyethyl substituent prevents the inhibitor from the correct interaction with the protein. The epoxide

• and benzyl group of subunit A are pointing away from the binding pocket. Docking of 24 to β-tubulin. Surface and backbone of β-tubulin are shown in blue, GDP in yellow. H-bonding (yellow dots) was detected with Lys176 and Asp179 in magenta. The benzyl group and the epoxide of subunit A are directed

One hundred years of benzotropone chemistry

• Arif Dastan,
• Haydar Kilic and
• Nurullah Saracoglu

Beilstein J. Org. Chem. 2018, 14, 1120–1180, doi:10.3762/bjoc.14.98

A stereoselective and flexible synthesis to access both enantiomers of N-acetylgalactosamine and peracetylated N-acetylidosamine

• Bettina Riedl and
• Walther Schmid

Beilstein J. Org. Chem. 2018, 14, 856–860, doi:10.3762/bjoc.14.71

• -catalyzed, stereo- and regioselective epoxide opening and subsequent nucleophilic substitution of an azide functionality. This approach enables the synthesis of the naturally D- and unnaturally L-configured GalNAc, as well as both enantiomers of the largely unknown N-acetylidosamine (IdoNAc). Keywords

• stereocenter on C4, resulting in the desired cis-selective epoxide opening and therefore, galacto-configured azido alcohols 7a and 7b (≥95% de) [22]. Initial limitations in reaction size and yield could have been overcome by switching the solvent from THF, as described in the Miyashita protocol, to EtOH. This

• approach opens up new perspectives for additional modifications: meso-tartaric acid as possible starting material or different epoxide opening protocols, as well as, the selective isotopic labelling are only a few to mention. This convertible synthetic route brings us a step closer to access the whole

Nanoreactors for green catalysis

• M. Teresa De Martino,
• Loai K. E. A. Abdelmohsen,
• Floris P. J. T. Rutjes and
• Jan C. M. van Hest

Beilstein J. Org. Chem. 2018, 14, 716–733, doi:10.3762/bjoc.14.61

• epoxide with phenylboronic acid was realized with 2% of pincer catalyst, the rate was 100 times higher for the water-based micellar system compared to the same reaction in organic solvent with the unsupported Pd-complex. A 100 times lower amount of catalyst was also loaded (0.02%), and still the reaction

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

• with DIBAl-H to 26 that was converted into the epoxide 27a by Sharpless epoxidation with (+)-L-DET. Treatment with TBSOTf and Hünig’s base resulted in opening of the epoxide with concomitant hydride migration to yield 28a. The stereochemical course for this reaction has been reported by Jung and

The synthesis of the 2,3-difluorobutan-1,4-diol diastereomers

• Robert Szpera,
• Nadia Kovalenko,
• Kalaiselvi Natarajan,
• Nina Paillard and
• Bruno Linclau

Beilstein J. Org. Chem. 2017, 13, 2883–2887, doi:10.3762/bjoc.13.280

• substituents is of interest. Here we describe optimisation efforts in the synthesis of anti-2,3-difluorobutane-1,4-diol, as well as the synthesis of the corresponding syn-diastereomer. Both targets were synthesised using an epoxide opening strategy. Keywords: acetal isomerization; deoxyfluorination; epoxide

• -difluorobutane-1,4-diol (anti-5) starting from commercially available cis-but-2-ene-1,4-diol (Scheme 1) [17]. The vicinal-difluoride group was introduced by a two-step sequence, with initial nucleophilic epoxide [18] opening by a fluoride source [19], followed by nucleophilic deoxyfluorination [9][10][11]. In

•  1 was high-yielding [17], two disadvantages were apparent. First, the epoxide opening takes 2.5 days at 115 °C and uses an expensive fluoride source (Landini’s reagent [18]: Bu4NH2F3). It was found that Bu4NH2F3 made in-house gave significantly reduced yields. Second, the use of the benzyl ether

Synthesis of ergostane-type brassinosteroids with modifications in ring A

• Vladimir N. Zhabinskii,
• Darya A. Osiyuk,
• Yuri V. Ermolovich,
• Natalia M. Chaschina,
• Tatsiana S. Dalidovich,
• Miroslav Strnad and
• Vladimir A. Khripach

Beilstein J. Org. Chem. 2017, 13, 2326–2331, doi:10.3762/bjoc.13.229

• preparation of BS 4 and 5 with a 2,3-epoxide moiety (Scheme 1). To date, only the corresponding 6-ketones were found in natural sources (2,3-diepisecasterone [10] with an α-oriented epoxide 4 and two BS with a β-oriented epoxide 5: secasterone [10][17] and 24-episecasterone [18]). The synthesis of both

• [19]. The 7-membered B ring in 21 had no influence on the stereochemical outcome of the reaction with MCPBA which resulted in the formation of the α-epoxide 22. The same was true for the electrophilic addition of Br+ to the olefinic unit of 21. It produced the trans-diaxial bromohydrine 23 that was

• transformed, on treatment with KOH, into the epoxide 24. The structures of isomeric epoxides 22 and 24 were confirmed by their NOESY spectra as shown in Scheme 4. The obvious NOE correlation between H-3 and H-5 in 24 suggested the spatial vicinity of these two protons, thus the epoxide ring was β-oriented. On

Homologated amino acids with three vicinal fluorines positioned along the backbone: development of a stereoselective synthesis

• Raju Cheerlavancha,
• Ahmed Ahmed,
• Yun Cheuk Leung,
• Aggie Lawer,
• Qing-Quan Liu,
• Marina Cagnes,
• Hee-Chan Jang,
• Xiang-Guo Hu and
• Luke Hunter

Beilstein J. Org. Chem. 2017, 13, 2316–2325, doi:10.3762/bjoc.13.228

• have previously reported a concise method for synthesising compounds that contain three vicinal C–F bonds [34]; their method commences with an epoxy alcohol, which undergoes three successive nucleophilic substitutions with fluoride (i.e., deoxyfluorination of the alcohol, epoxide ring opening with

• Et3N·3HF according to O’Hagan’s method [34] (Scheme 3). This did effect epoxide-opening to some extent, but the reaction was rather unsatisfactory because it was low-yielding and non-regioselective, which made full characterisation of the product mixture (32/33) impossible. Nevertheless, an analytical

• it was found that the inclusion of the additive TMS-morpholine [36][37] was also required to ensure a high diastereoisomeric excess of 38a. The epoxide 38a was then ring-opened using Et3N·3HF to deliver the difluorodiol 39a as a mixture of regioisomers. This mixture subsequently converged during the

Synthesis of substituted Z-styrenes by Hiyama-type coupling of oxasilacycloalkenes: application to the synthesis of a 1-benzoxocane

• James R. Vyvyan,
• Courtney A. Engles,
• Scott L. Bray,
• Erik D. Wold,
• Christopher L. Porter and
• Mikhail O. Konev

Beilstein J. Org. Chem. 2017, 13, 2122–2127, doi:10.3762/bjoc.13.209

• have recently been reviewed [34]. We have previously reported syntheses of heliannuols C, D, and E via intramolecular epoxide opening reactions [35][36], but this approach did not translate well to the synthesis of heliannuol A. One of our alternative strategies for the synthesis of heliannuol A was an