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

• % yield). Next, the major product 158 was converted into 159 by isomerization via DBU in 82% yield. The cis-lactone 159 was found to be a core structural unit present in umbellactal (Scheme 32). Ghosh and co-workers also reported [37] a short and efficient approach to a highly functionalized lactarane

Dimethylamine as the key intermediate generated in situ from dimethylformamide (DMF) for the synthesis of thioamides

• Weibing Liu,
• Cui Chen and
• Hailing Liu

Beilstein J. Org. Chem. 2015, 11, 1721–1726, doi:10.3762/bjoc.11.187

• ). The reaction is completed after 4 h at 120 °C, providing 4-methoxy-N,N-dimethylbenzothioamide (2a) with 64% yield by using sodium acetate (AcONa) as the base (Table 1, entry 2). With regard to the catalytic activity of different bases (Table 1, entries 4–8), 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU

An efficient synthesis of N-substituted 3-nitrothiophen-2-amines

• Sundaravel Vivek Kumar,
• Shanmugam Muthusubramanian,
• J. Carlos Menéndez and
• Subbu Perumal

Beilstein J. Org. Chem. 2015, 11, 1707–1712, doi:10.3762/bjoc.11.185

• with ethanol to give the pure 3-nitro-N-(p-tolyl)thiophen-2-amine (3e) without the need for chromatography. Then the model reaction was further investigated by employing alternative bases such as 1,4-diazabicyclo[2.2.2]octane (DABCO, Table 1, entry 4), 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU, Table 1

Advances in the synthesis of functionalised pyrrolotetrathiafulvalenes

• Luke J. O’Driscoll,
• Sissel S. Andersen,
• Marta V. Solano,
• Dan Bendixen,
• Morten Jensen,
• Troels Duedal,
• Jess Lycoops,
• Cornelia van der Pol,
• Rebecca E. Sørensen,
• Karina R. Larsen,
• Kenneth Myntman,
• Christian Henriksen,
• Stinne W. Hansen and
• Jan O. Jeppesen

Beilstein J. Org. Chem. 2015, 11, 1112–1122, doi:10.3762/bjoc.11.125

• functionalised with thioethers, exemplified by a series of ethylene glycol derivatives. Additionally, the merits of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) as an alternative to the most common deprotecting agent, CsOH·H2O are discussed. Finally, we show how a copper-mediated Ullman-type reaction can be applied

• in many cases the use of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU, Scheme 5), rather than CsOH·H2O, allows for a more convenient and consistent synthesis with a comparable or higher yield, which is also easier to conduct on a larger scale. DBU is an easily handled liquid which can be directly added to

• , a side reaction which can be caused by the presence of small quantities of methoxide ions in the reaction mixture. As DBU is a non-nucleophilic base, such deprotection cannot occur. Note that unlike in the case of CsOH·H2O it is important to heat reactions using DBU to achieve good conversion. Thus

DBU-promoted carboxylative cyclization of o-hydroxy- and o-acetamidoacetophenone

• Wen-Zhen Zhang,
• Si Liu and
• Xiao-Bing Lu

Beilstein J. Org. Chem. 2015, 11, 906–912, doi:10.3762/bjoc.11.102

• -diazabicycloundec-7-ene (DBU) is reported. This reaction provides convenient access to the biologically important compounds 4-hydroxy-2H-chromen-2-one and 4-hydroxy-2(1H)-quinolinone in moderate to good yields using carbon dioxide as the carboxylation reagent. An acyl migration from nitrogen to carbon is observed

• carbonate at 130–170 °C, yielding 4-hydroxy-2H-chromen-2-ones in moderate yields [21]. From the viewpoints of solubility, efficiency, and ease of recovery and reuse, the use of an organic base rather than potassium carbonate in this reaction would be more promising. DBU and MTBD were previously reported as

• suitable bases to promote the carboxylation of α-C–H bonds in aromatic ketones with carbon dioxide [17][18][19][20]. In extension of our continuous efforts in developing catalytic transformations of carbon dioxide into value-added fine chemicals [20][22][23], we report herein the DBU-promoted carboxylative

Thiazole formation through a modified Gewald reaction

• Carl J. Mallia,
• Lukas Englert,
• Gary C. Walter and
• Ian R. Baxendale

Beilstein J. Org. Chem. 2015, 11, 875–883, doi:10.3762/bjoc.11.98

• conversion and isolated yield (58%) with tetramethylethylenediamine (TMEDA) also giving a respectable yield of 50% (Table 1, entries 1 and 10). The stronger guanidine bases 1,1,3,3-tetramethylguanidine (TMG) and 1,8-diazabicycloundec-7-ene (DBU) both gave full consumption of the nitrile starting material

• , but generated complicated product mixtures allowing only a moderate isolated yield of 33% for the TMG and negligible recovery for the DBU (Table 1, entries 7 and 8). Interestingly, the use of piperidine led to no conversion under these reaction conditions (Table 1, entry 9), we believe this is due to

Synthesis of carbohydrate-scaffolded thymine glycoconjugates to organize multivalency

• Anna K. Ciuk and
• Thisbe K. Lindhorst

Beilstein J. Org. Chem. 2015, 11, 668–674, doi:10.3762/bjoc.11.75

• . Figure 1B). Based on our earlier work [5], we first planned to employ an appropriate bromoalkyl mannoside for N-alkylation of the thymine N3 [28]. In this step, DBU can be employed as non-nucleophilic base [29] leaving the NHBoc group intact. When sodium hydride is employed instead, NHBoc is deprotonated

• optimized procedure employing DBU and TBAI at rt [5] over two days to deliver the protected glycothymine derivative 12 in 64% yield. The acetyl protecting groups were cleaved employing Zemplén’s procedure [30]. During work-up with acidic ionic exchange resin, surprisingly cleavage of the isopropylidene

Synthesis of the furo[2,3-b]chromene ring system of hyperaspindols A and B

• Danielle L. Paterson and
• David Barker

Beilstein J. Org. Chem. 2015, 11, 265–270, doi:10.3762/bjoc.11.29

• representation of 7a. 3D representation of 7b. Possible mechanism for the formation of furo[2,3-b]chromenes 7a and 7b. Reagents and conditions: (i) triethylphosphonoacetate, DBU, THF, 48 h, 94%; (ii) H2, 10% Pd/C, EtOAc, 3 h, quant; (iii) BnBr, K2CO3, DMF, 3 h, 88%; (iv) LDA, THF, −78 °C, then allyl bromide, 24

Natural phenolic metabolites with anti-angiogenic properties – a review from the chemical point of view

• Qiu Sun,
• Jörg Heilmann and
• Burkhard König

Beilstein J. Org. Chem. 2015, 11, 249–264, doi:10.3762/bjoc.11.28

• , −40 °C; −40 °C → rt, 3 h; (2) Na2S2O4, rt, 30 min; (c) MeOH/H2O 1:1, reflux. Synthesis of quinolone-substituted phenol 20. Reagents and conditions: (a) Ac2O, 2-hydroxybenzaldehyde, 130 °C; (b) (1) Br2, AcOH, (2) Ac2O; (c) (1) DBU, THF, (2) Ac2O; (d) Na2CO3, MeOH/THF. Synthesis of quinolone-substituted

Cross-dehydrogenative coupling for the intermolecular C–O bond formation

• Igor B. Krylov,
• Vera A. Vil’ and
• Alexander O. Terent’ev

Beilstein J. Org. Chem. 2015, 11, 92–146, doi:10.3762/bjoc.11.13

• nucleophilic attack by the alcohol to form ester 108. The mechanism of the aerobic oxidative coupling of benzaldehyde with methanol in the presence of the 4-ethyl-1-methyl-1H-1,2,4-triazolium iodide/DBU system was studied in detail [114]. It was shown that the reaction proceeds via another mechanism, involving

• salt 109 combined with triethylamine acted as the catalyst, and azobenzene 110 served as the oxidizing agent. Esters 111 were prepared in 16–97% yield. The selective oxidative coupling of aldehydes 112 and alcohols 113 in the presence of amines 114 using 1,4-dimethyltriazolium iodide (115), DBU and

Articulated rods – a novel class of molecular rods based on oligospiroketals (OSK)

• Pablo Wessig,
• Roswitha Merkel and
• Peter Müller

Beilstein J. Org. Chem. 2015, 11, 74–84, doi:10.3762/bjoc.11.11

• characterized. Only with CuBr in the presence of DBU [20] we received evidence for a cyclization of 15 from IR and MS spectra. At this point we could not rule out that polymerization of 15 occurred instead of the desired cyclization. On the other hand it was obvious that the cyclization product can be insoluble

• a similar strategy as described above for articulated rod 15. Accordingly, articulated rod 25 was obtained in nine steps (Scheme 4). To our delight, 25 could be successfully cyclized to 26 using the above mentioned CuBr/DBU catalyst albeit with moderate yield (Scheme 5). After having demonstrated

A facile synthesis of functionalized 7,8-diaza[5]helicenes through an oxidative ring-closure of 1,1’-binaphthalene-2,2’-diamines (BINAMs)

• Youhei Takeda,
• Masato Okazaki,
• Yoshiaki Maruoka and
• Satoshi Minakata

Beilstein J. Org. Chem. 2015, 11, 9–15, doi:10.3762/bjoc.11.2

• organic bases like DABCO (pKa 8.93 in DMSO [32]) and DBU (pKa 23.9 in MeCN [33]) gave a lower yield (32%) and no product, respectively (Table 1, entries 14 and 15). As results, the use of the moderately weak organic base 2,6-lutidine (pKa 6.72 in water [34]) successfully afforded 2a in high yield (Table 1

Synthetic strategies for the fluorescent labeling of epichlorohydrin-branched cyclodextrin polymers

• Milo Malanga,
• Mihály Bálint,
• István Puskás,
• Kata Tuza,
• Tamás Sohajda,
• László Jicsinszky,
• Lajos Szente and
• Éva Fenyvesi

Beilstein J. Org. Chem. 2014, 10, 3007–3018, doi:10.3762/bjoc.10.319

• kDa (1.4% of the starting weight). 3) Fluorescent labeling The coupling between rhodamine isothiocyanate (RBITC) and compound 2 was performed in pyridine and the addition of an extra base (DBU) contributed to the progression of the reaction (Scheme 2). As in the case of the fluorescent labeling of

Synthesis of the pentasaccharide repeating unit of the O-antigen of E. coli O117:K98:H4

• Pintu Kumar Mandal

Beilstein J. Org. Chem. 2014, 10, 2724–2728, doi:10.3762/bjoc.10.287

• hemeacetal thus obtained was reacted with trichloroacetonitrile in the presence of DBU [34] to afford the desired disaccharide trichloroacetimidate derivative 14 in 77% yield. It was used directly without further purification [17] (Scheme 2). Finally, glycosylation of trisaccharide acceptor 11 with the

• ) PPh3, THF, 6 h, then Ac2O, pyridine, rt, 1 h, 84%;(g) CAN, CH3CN, H2O, rt, 1.5 h; (h) CCl3CN, DBU, CH2Cl2, −10 °C, 1 h; (i) NOBF4, CH2Cl2, −15 °C, 1 h, 70%; (j) i) NH2NH2·H2O, CH3CH2OH, 80 °C, 8 h, ii) acetic anhydride, pyridine, rt, 1 h; (k) H2, 20% Pd(OH)2/C, CH3OH, rt, 24 h; (l) 0.1 M CH3ONa, CH3OH

Synthesis of graft polyrotaxane by simultaneous capping of backbone and grafting from rings of pseudo-polyrotaxane

• Kazuaki Kato,
• Katsunari Inoue,
• Masabumi Kudo and
• Kohzo Ito

Beilstein J. Org. Chem. 2014, 10, 2573–2579, doi:10.3762/bjoc.10.269

• enough to form an inclusion complex with α-CD, the smallest CD [17]. In addition, DBU was employed not only as a polymerization catalyst but also as a base to prevent hydrogen bond formation between CDs, so that the ring components would disperse on the backbone. However, this can also induce the

• by the SEC peak corresponding to Mn = 11,000 and Mw = 15,000 (run 4). These results suggested accelerated dethreading at high temperatures, although it is unknown whether dethreading occurred before or after the grafting reaction. The polymerization was initiated by DBU, a strong base, which

• a base [18]. Notably, the direct grafting from polyrotaxane with tin catalysts rather than DBU yielded a cross-linked GPR as a gel-like insoluble solid, indicating the necessity of the dissociation of the columnar crystal. Accordingly, GPR is not obtained if the polymerization from the ends of the

Superoxide chemistry revisited: synthesis of tetrachloro-substituted methylenenortricyclenes

• Basavaraj M. Budanur and
• Faiz Ahmed Khan

Beilstein J. Org. Chem. 2014, 10, 2531–2538, doi:10.3762/bjoc.10.264

• upfield shift (δ = ~1.6) for the anti-methyl protons in the pentachloro DA adducts 3. Having adduct 3a in hand, we turned our attention to a dehydrochlorination to create a double bond at the C-7 position. Unfortunately the use of conventional bases like KOt-Bu, DBU, 2,6-lutidine, NaOH and NaOMe did not

A simple copper-catalyzed two-step one-pot synthesis of indolo[1,2-a]quinazoline

• Chunpu Li,
• Lei Zhang,
• Shuangjie Shu and
• Hong Liu

Beilstein J. Org. Chem. 2014, 10, 2441–2447, doi:10.3762/bjoc.10.254

• replaced with Cs2CO3 as the base (Table 1, entry 7). However, when a weaker base (K3PO4) or an organic base (DBU) was used, the conversions of starting materials were lower (Table 1, entries 8 and 9). Some other solvents were investigated, iPrOH resulted in only trace of product, while no product was

Photorelease of phosphates: Mild methods for protecting phosphate derivatives

• Sanjeewa N. Senadheera,
• Abraham L. Yousef and
• Richard S. Givens

Beilstein J. Org. Chem. 2014, 10, 2038–2054, doi:10.3762/bjoc.10.212

• °C, 45 min; b) TBSCl, Et3N, DBU, CH2Cl2, rt, 28 h; c) CuBr2, 1:1 CHCl3/EtOAc; d) KHSO4, MeOH (aq), CH2Cl2, rt, 43 h; e) tetramethylammonium diethyl phosphate, DMF, 55 °C, 2–3 h; f) Ac2O, AlCl3, CH2Cl2, 0 °C to rt over 3 h then stirred at rt. Synthesis of diethyl 8-(benzyloxy)quinolin-5-yl)-2-oxoethyl

Efficient CO₂ capture by tertiary amine-functionalized ionic liquids through Li⁺-stabilized zwitterionic adduct formation

• Zhen-Zhen Yang and
• Liang-Nian He

Beilstein J. Org. Chem. 2014, 10, 1959–1966, doi:10.3762/bjoc.10.204

• , PEG150MeTMG and PEG150MeBu2N), all the O and N atoms coordinate with Li+ in a quasi-aza-crown ether fashion. OctIm, OctTMG, TMG, DBU and DBN generate complexes whereby Li+ is bound only to N atoms. In contrast, the coordination ability of the N atom in OctBu2N is not strong enough to form a homogeneous

Facile synthesis of 1-alkoxy-1H-benzo- and 7-azabenzotriazoles from peptide coupling agents, mechanistic studies, and synthetic applications

• Mahesh K. Lakshman,
• Manish K. Singh,
• Mukesh Kumar,
• Raghu Ram Chamala,
• Vijayender R. Yedulla,
• Domenick Wagner,
• Evan Leung,
• Lijia Yang,
• Asha Matin and
• Sadia Ahmad

Beilstein J. Org. Chem. 2014, 10, 1919–1932, doi:10.3762/bjoc.10.200

• the presence of a base. Thus, we first evaluated whether the reaction of BOP with alcohols was general and we elected to use DBU as base for cost considerations. Table 1 shows the results of this analysis. Reaction of BOP with either 1.4 or 2.7 molar equiv of MeOH, in the presence of 1.4 molar equiv

• of DBU, gave comparable yields of Bt-OMe (1a, 48% and 50%, respectively). Use of MeOH as reaction solvent itself resulted in a 47% yield of 1a. These results seem to imply that maximal conversion of BOP to the N-alkoxybenzotriazoles is around 50%, possibly due to a competing reaction between BOP and

• DBU (see below). Nevertheless, 1° and 2° alcohols appear to react with BOP in the presence of a base, leading to the direct formation of N-alkoxybenzotriazoles. Because reactions with BOP produce HMPA, a suspected nasal carcinogen, and the modest yields of the N-alkoxybenzotriazoles obtained, we

Concise total synthesis of two marine natural nucleosides: trachycladines A and B

• Haixin Ding,
• Wei Li,
• Zhizhong Ruan,
• Ruchun Yang,
• Zhijie Mao,
• Qiang Xiao and
• Jun Wu

Beilstein J. Org. Chem. 2014, 10, 1681–1685, doi:10.3762/bjoc.10.176

• -dichloropurine (18) afforded nucleoside 16 in 86% yield with DBU as a base and TMSOTf as a Lewis acid (Scheme 3). After heated in a pressure tube with ammonia saturated methanol, the benzoyl protecting groups were removed and the chlorine atom at position C6 was substituted at the same time to afford

• ) AMPDA, phosphate buffer at pH 5.6 and 40 °C, 97%. Synthesis of trachycladine A (1). Reagents and conditions: (a) DBU, TMSOTf, CH3CN, 86%; (b) NH3 sat. methanol, sealed press tube, 92%. Supporting Information Supporting Information File 471: Detailed experimental procedures, characterization data of

Multivalent scaffolds induce galectin-3 aggregation into nanoparticles

• Candace K. Goodman,
• Mark L. Wolfenden,
• Pratima Nangia-Makker,
• Anna K. Michel,
• Avraham Raz and
• Mary J. Cloninger

Beilstein J. Org. Chem. 2014, 10, 1570–1577, doi:10.3762/bjoc.10.162

• mL). After cooling the mixture in an ice bath, DBU (60 mg, 0.32 mmol) was added drop-wise and the mixture was stirred for 3 h. The reaction mixture was dissolved in CH2Cl2 (30 mL), and the organic layer was washed with brine (2 × 10 mL) and water (2 × 10 mL), dried over MgSO4, filtered and the

Efficient routes toward the synthesis of the D-rhamno-trisaccharide related to the A-band polysaccharide of Pseudomonas aeruginosa

• Aritra Chaudhury,
• Sajal K. Maity and
• Rina Ghosh

Beilstein J. Org. Chem. 2014, 10, 1488–1494, doi:10.3762/bjoc.10.153

• blocks; reagents and conditions: i) Pyr., BzCl, 0 °C–rt; ii) PhC(OMe)3, CSA, MeCN, 0 °C–rt, 80% AcOH (aq), 25 °C; iii) DTBP, TIPST, octane, reflux; iv) TCCA, acetone–H2O, rt; v) CCl3CN, DBU, DCM; vi) MeC(OEt)3, CSA, MeCN, 0 °C–rt, 80% AcOH (aq), 25 °C. Sequential stepwise synthesis of the trisaccharide

Design, automated synthesis and immunological evaluation of NOD2-ligand–antigen conjugates

• Marian M. J. H. P. Willems,
• Gijs G. Zom,
• Nico Meeuwenoord,
• Ferry A. Ossendorp,
• Herman S. Overkleeft,
• Gijsbert A. van der Marel,
• Jeroen D. C. Codée and
• Dmitri V. Filippov

Beilstein J. Org. Chem. 2014, 10, 1445–1453, doi:10.3762/bjoc.10.148

• MurNAc 10 in 93% yield [39][40]. Fully protected MDP 14 was obtained by condensation of acid 10 and dipeptide 13. To this end, Fmoc-protected tert-butyl glutamic acid 11 was reacted with di-tert-butyl dicarbonate and transformed into 12 [41]. In a one-pot procedure compound 12 was deprotected with DBU

• , quant.; c) CSA, PhCH(OMe)2, MeCN, DMF, 86%; d) (S)-2-chloropropionic acid, NaH, 1,4-dioxane, 93%; e) Boc2O, NH4HCO3, pyridine, 1,4-dioxane, 99%; f) 1) DBU, HOBt, DCM; 2) Fmoc-L-Ala-OH, EDC, DIPEA, DCM, 82%; g) 1) 13, DBU, HOBt, DCM; 2) 12, HATU, DIPEA, DCM, 70%; h) 1) Me3P (solution in THF), DMF, THF

A complete series of 6-deoxy-monosubstituted tetraalkylammonium derivatives of α-, β-, and γ-cyclodextrin with 1, 2, and 3 permanent positive charges

• Martin Popr,
• Simona Hybelbauerová and
• Jindřich Jindřich

Beilstein J. Org. Chem. 2014, 10, 1390–1396, doi:10.3762/bjoc.10.142

• step, the installed triamine was quaternized by methylation with MeI. To achieve a full conversion, the use of a sterically hindered base was necessary. First, we attempted to methylate intermediate 27 containing a diethylenetriamine moiety. Different bases (K2CO3, 2,6-lutidine, 2,4,6-collidine and DBU