Why do thioureas and squaramides slow down the Ireland–Claisen rearrangement?

• Dominika Krištofíková,
• Juraj Filo,
• Mária Mečiarová and
• Radovan Šebesta

Beilstein J. Org. Chem. 2019, 15, 2948–2957, doi:10.3762/bjoc.15.290

• -N-methylcyclohexanamine (65%, Scheme 2) whereas reactions with trihexylamine and diisopropylethylamine provided the product 3c with lower yields. Rearrangement in the presence of N-methylmorpholine, quinine, and N-methylpyrrolidine afforded only traces of acid 3c and reactions with DBU, DABCO and (S

Recent advances in transition-metal-catalyzed incorporation of fluorine-containing groups

• Xiaowei Li,
• Xiaolin Shi,
• Xiangqian Li and
• Dayong Shi

Beilstein J. Org. Chem. 2019, 15, 2213–2270, doi:10.3762/bjoc.15.218

Installation of -SO₂F groups onto primary amides

• Jing Liu,
• Shi-Meng Wang,
• Njud S. Alharbi and
• Hua-Li Qin

Beilstein J. Org. Chem. 2019, 15, 1907–1912, doi:10.3762/bjoc.15.186

• assembly of N-fluorosulfonyl amides from cheap and abundant reagent is highly desirable. Herein, we report the first, to the best of our knowledge, SO2F2-mediated N-fluorosulfonylation [40][41][42] of amides by using DBU as base for the constructions of a series N-fluorosulfonyl amides (Scheme 1b). Results

• in 25% yield (Table 1, entry 1). Encouraged by this preliminary success, several common bases were evaluated, among which, 1,8-diazabicycloundec-7-ene (DBU) catalysed the proposed transformation most effectively to provide the desired product 2a in nearly quantitative yield (Table 1, entries 2–7

• ). Subsequently, different solvents were screened (Table 1, entries 5, 8–12) and DMSO was found to be the best option. Decreasing the temperature from 50 °C to 40 °C or even room temperature, or cutting down the amount of DBU to 4 equivalents resulted in decreased yields (Table 1, entries 13–15). With the

A metal-free approach for the synthesis of amides/esters with pyridinium salts of phenacyl bromides via oxidative C–C bond cleavage

• Kesari Lakshmi Manasa,
• Yellaiah Tangella,
• Namballa Hari Krishna and
• Mallika Alvala

Beilstein J. Org. Chem. 2019, 15, 1864–1871, doi:10.3762/bjoc.15.182

• reaction (Table 1, entry 5). Next, we focused our attention on screening of other bases such as KOH, NaOH, t-BUOK, Na2CO3, Et3N and DBU. It was observed that K2CO3 is superior to other organic and inorganic bases employed (Table 1, entries 6–11). To further understand the effect of solvent a series of

Complexation of 2,6-helic[6]arene and its derivatives with 1,1′-dimethyl-4,4′-bipyridinium salts and protonated 4,4'-bipyridinium salts: an acid–base controllable complexation

• Jing Li,
• Qiang Shi,
• Ying Han and
• Chuan-Feng Chen

Beilstein J. Org. Chem. 2019, 15, 1795–1804, doi:10.3762/bjoc.15.173

• shown in Figure 7, when 2.2 equiv of DBU were added into the solution of complex H2·G4 in CD2Cl2, the signals for protons 3 and 6 of complex H2·G4 disappeared while the proton signals of free H2 and 4,4'-bipyridine were observed, which indicated that the complex dissociated. On the other hand, when 2.2

• DBU, (c) to the solution of b were added 2.2 equiv of TFA, and (d) free 4,4'-bipyridine. [H2]0 = 2.0 mM. Synthesis of hosts H3–5. Association constants (Ka) for 1:1 host–guest complexes in CDCl3/acetone-d6 1:2 (v/v) at 298 K. Association constants (Ka) for the 1:1 host–guest complexes in different

N-(1-Phenylethyl)aziridine-2-carboxylate esters in the synthesis of biologically relevant compounds

• Iwona E. Głowacka,
• Aleksandra Trocha,
• Andrzej E. Wróblewski and
• Dorota G. Piotrowska

Beilstein J. Org. Chem. 2019, 15, 1722–1757, doi:10.3762/bjoc.15.168

Recent advances on the transition-metal-catalyzed synthesis of imidazopyridines: an updated coverage

• Gagandeep Kour Reen,
• Ashok Kumar and
• Pratibha Sharma

Beilstein J. Org. Chem. 2019, 15, 1612–1704, doi:10.3762/bjoc.15.165

Synthesis and conformational preferences of short analogues of antifreeze glycopeptides (AFGP)

• Małgorzata Urbańczyk,
• Michał Jewgiński,
• Joanna Krzciuk-Gula,
• Jerzy Góra,
• Rafał Latajka and
• Norbert Sewald

Beilstein J. Org. Chem. 2019, 15, 1581–1591, doi:10.3762/bjoc.15.162

• the resin. After two minutes the diisopropyl azodicarboxylate (DIAD) solution was added dropwise to the reaction mixture. Once the reaction was complete, the o-NBS protecting group was removed by using 2-mercaptoethanol and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU). The Kaiser test did not reveal any

• -diazabicyclo[5.4.0]undec-7-ene (DBU) in NMP, which were shaken with the resin for 2 hours, and the reaction was repeated. Modified PS-Sieber resin was loaded manually with Fmoc-ʟ-Ala-OH or Fmoc-ᴅ-Ala-OH (4 equiv), 1-hydroxy-7-azabenzotriazole (HOAt, 4 equiv), O-(7-azabenzotriazol-1-yl)-N,N,N’,N

• , 10 equiv), DIAD (5 equiv), THF, rt, 2 h, twice; d. HSCH2CH2OH (10 equiv), DBU (5 equiv), NMP, rt, 2 h, twice; B) SPPS of model AFGP analogues 1 and 2: a. Fmoc-Ala-OH∙H2O (4 equiv), HOAt (4 equiv), HATU (4 equiv), DIEA (8 equiv), NMP, rt, 2 h; b. piperidine 20% v/v in DMF 3 × 10 min; c. Fmoc-L-Thr(α

A novel three-component reaction between isocyanides, alcohols or thiols and elemental sulfur: a mild, catalyst-free approach towards O-thiocarbamates and dithiocarbamates

• András György Németh,
• György Miklós Keserű and
• Péter Ábrányi-Balogh

Beilstein J. Org. Chem. 2019, 15, 1523–1533, doi:10.3762/bjoc.15.155

• isocyanide component under air. In the case of using other bases, such as caesium carbonate (Cs2CO3), diisopropylethylamine (DIPEA) or sodium ethoxide (NaOEt), only the isothiocyanate intermediate of the reaction was isolated (Table 1, entries 17, 18, and 20). However, using diazabicycloundecene (DBU) as the

• crude product are attached in Supporting Information File 1. Several experiments were performed to discover the reaction conditions that enable the synthesis of O-aryl thiocarbamates. Initially, DBU was used in refluxing dioxane, as this base was shown to provide the appropriate aliphatic O

Introduction of an isoxazoline unit to the β-position of porphyrin via regioselective 1,3-dipolar cycloaddition reaction

• Xiujun Liu,
• Xiang Ma and
• Yaqing Feng

Beilstein J. Org. Chem. 2019, 15, 1434–1440, doi:10.3762/bjoc.15.143

• the β-position, a Wittig reaction was performed, in which the porphyrin phosphonium salt 1 reacted with 4-MeCO2-benzaldehyde in the presence of DBU to furnish the double bond, followed by insertion of Zn ions into the porphyrin cavity to give compound 2. Nitrile oxides [45] as one of the most reactive

• , 1H, β-pyrrolic H), 8.76–8.86 (m, 5H, β-pyrrolic H). 2: To the solution of compound 1 (0.10 g, 0.11 mmol) and 4-methoxycarbonylbenzaldehyde (18 mg, 0.11 mmol) in CH2Cl2 (20 mL) was added DBU (83 mg, 0.55 mmol, 5.0 equiv vs 1). The reaction mixture was stirred for 8 hours. H2O (15 mL) was added to

Understanding the unexpected effect of frequency on the kinetics of a covalent reaction under ball-milling conditions

• Ana M. Belenguer,
• Adam A. L. Michalchuk,
• Giulio I. Lampronti and
• Jeremy K. M. Sanders

Beilstein J. Org. Chem. 2019, 15, 1226–1235, doi:10.3762/bjoc.15.120

• of bis(2-nitrophenyl) disulfide and bis(4-chlorophenyl) disulfide in the presence of a small amount of the base catalyst 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) to produce 4-chlorophenyl 2-nitrophenyl disulfide (see Scheme 1). Reliable experimental procedures have already been established for this

• the progress of product formation as a function of grinding time. Purposely designed stability experiments of the ball mill NG and LAG reactions were conducted by interrupting the milling experiments of 1-1 + 2-2 + DBU at different times and storing the grinding jars sealed. After several months and

• ) conditions with 50 μL of acetonitrile added to 200 mg of powder. The kinetic points prepared for this study are all single point experiments. The reaction under study is a base-catalyzed disulfide exchange reaction starting from equimolar amounts of homodimers using DBU as the base catalyst to result in the

Electrophilic oligodeoxynucleotide synthesis using dM-Dmoc for amino protection

• Shahien Shahsavari,
• Dhananjani N. A. M. Eriyagama,
• Bhaskar Halami,
• Vagarshak Begoyan,
• Marina Tanasova,
• Jinsen Chen and
• Shiyue Fang

Beilstein J. Org. Chem. 2019, 15, 1116–1128, doi:10.3762/bjoc.15.108

• [35][36][37][38]. The requirement of the strong base DBU in aprotic solvents over long hours in the presence of a nucleophilic scavenger for their cleavage could limit their application. In addition, in some cases the sequences synthesized by the method were short and the yields of the ODNs were low

• '-trityl group was not removed. More details about the synthesis are given in the Experimental section. For cleavage and deprotection under non-nucleophilic conditions, the ODN on CPG, which should appear as 31 (Scheme 4) with a 5'-trityl tag, was treated with a DBU solution in acetonitrile at room

• temperature briefly. This removed the β-cyanoethyl phosphate protecting groups to give 32. HPLC analysis of the DBU solution did not found any ODN that was cleaved prematurely – an observation consistent with the slow rate of cleavage of succinyl-anchored ODNs from solid support under similar conditions [50

Mechanochemical synthesis of poly(trimethylene carbonate)s: an example of rate acceleration

• Sora Park and
• Jeung Gon Kim

Beilstein J. Org. Chem. 2019, 15, 963–970, doi:10.3762/bjoc.15.93

• from low reactivity. The solvent-free mechanochemical polymerization of trimethylene carbonate using the organocatalysts 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) and 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) are examined herein. The polymerizations under ball-milling conditions exhibited significant

• biomedical applications [24]. The amidine base 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) is one of the best studied and most popular organocatalysts for ring-opening polymerizations of cyclic carbonates and lactones [25][26][27]. In contrast to the high activity of lactone polymerization, cyclic carbonate

• polymerization usually requires long reaction times to achieve high conversions (Table 1) [27]. The DBU-catalyzed polymerization of trimethylene carbonate in chloroform, tetrahydrofuran, toluene, and methylene chloride converted less than 5% monomer into poly(trimethylene carbonate) (PTMC) within 1 h (Table 1

Efficient synthesis of pyrazolopyridines containing a chromane backbone through domino reaction

• Razieh Navari,
• Saeed Balalaie,
• Saber Mehrparvar,
• Fatemeh Darvish,
• Frank Rominger,
• Fatima Hamdan and
• Sattar Mirzaie

Beilstein J. Org. Chem. 2019, 15, 874–880, doi:10.3762/bjoc.15.85

• yield of pure product was increased to 65% in ethanol. The yield of the reaction in the presence of DBU and diisopropylethylamine (DIPEA) as a base were 61 and 60%, respectively. This means that the type of base does not play an effective role in this reaction. The effect of different solvents (EtOH

An improved synthesis of adefovir and related analogues

• David J. Jones,
• Eileen M. O’Leary and
• Timothy P. O’Sullivan

Beilstein J. Org. Chem. 2019, 15, 801–810, doi:10.3762/bjoc.15.77

• were unable to access 2 (Scheme 7). Instead, the major product isolated in both cases was novel heterocycle 35. It is likely that cleavage of one of the pivaloxymethyl groups, followed by intramolecular cyclisation, results in the formation of 35. Microwave heating of 33 in the presence of DBU also

Synthesis of functionalized diazocines for application as building blocks in photo- and mechanoresponsive materials

• Widukind Moormann,
• Daniel Langbehn and
• Rainer Herges

Beilstein J. Org. Chem. 2019, 15, 727–732, doi:10.3762/bjoc.15.68

• deprotection with TiCl4 the hydroxy-functionalized diazocines 4a and 4b were obtained [32]. The hydroxy groups in 4a and 4b were successfully converted into azides using 2-azido-1,3-dimethylimidazolinium hexafluorophosphate (ADMP) and DBU [33]. The synthesis was completed with a Staudinger reaction to obtain

• ; iii) Zn, Ba(OH)2 H2O/EtOH, and CuCl2/O2, NaOH/MeOH; iv) Ti(Cl)4, DCM; v) ADMP, DBU, THF; vi) PPh3, H2O, THF; viii) TsCl, DMAP, TEA, DCM, and t-BuOK, THF. Photostationary states (300 K), absorption maxima and half-lives (298.15 K), determined by 1H NMR and UV–vis spectroscopy in acetonitrile

Synthesis of the polyketide section of seragamide A and related cyclodepsipeptides via Negishi cross coupling

• Jan Hendrik Lang and
• Thomas Lindel

Beilstein J. Org. Chem. 2019, 15, 577–583, doi:10.3762/bjoc.15.53

• satisfying. After Boc removal at 22, HATU/HOAt-mediated coupling with Boc-protected L-alanine afforded dipeptide 26, which was saponified and coupled with TIPS-protected threonine methyl ester (obtained with TIPSCl/DBU/MeCN) to provide tripeptide 27 (Scheme 5). Peptides 26 and 27 were obtained in nearly

Synthesis and biological investigation of (+)-3-hydroxymethylartemisinin

• Toni Smeilus,
• Farnoush Mousavizadeh,
• Johannes Krieger,
• Xingzhao Tu,
• Marcel Kaiser and
• Athanassios Giannis

Beilstein J. Org. Chem. 2019, 15, 567–570, doi:10.3762/bjoc.15.51

• min, 95%; c) i. DBU, DCM, rt, 1 d; ii. TBAF, THF, 0 °C, 10 min, 87% (over two steps). LDA = lithium diisopropylamide, HMPA = hexamethylphosphoramide, DBU = 1,8-diazabicyclo[5.4.0]undec-7-ene, TESCl = triethylsilyl chloride. Supporting Information Supporting Information File 206: Experimental part.

Low-budget 3D-printed equipment for continuous flow reactions

• Jochen M. Neumaier,
• Amiera Madani,
• Thomas Klein and
• Thomas Ziegler

Beilstein J. Org. Chem. 2019, 15, 558–566, doi:10.3762/bjoc.15.50

• longer residence time resulted in a lower yield (10.5 min = 37%). Similar observations were previously made for glycosylation reaction under continuous flow conditions [23][24][25][26]. A larger amount of DBU did not increase the yield. For the glycosylation reactions with glycosyl donor 5 a multiple

• step reaction arrangement starting from pyranose 4 was set up. Scheme 4 shows this setup of a suitable cascade reaction in which DBU, trichloroacetonitrile and pyranose 4 were pumped through the first flow reactor (R1) followed by the addition of the alcohol and TMSOTf through the second reactor. Table

Convergent synthesis of the pentasaccharide repeating unit of the biofilms produced by Klebsiella pneumoniae

• Arin Gucchait,
• Angana Ghosh and
• Anup Kumar Misra

Beilstein J. Org. Chem. 2019, 15, 431–436, doi:10.3762/bjoc.15.37

• presence of DBU [34] resulted in the formation of (4,6-O-benzylidene-2,3-di-O-benzyl-β-D-mannopyranosyl)-(1→4)-6-O-benzoyl-2,3-di-O-benzyl-α,β-D-glucopyranosyl trichloroacetimidate (18) in 90% yield (Scheme 2). In the next set of reactions, the disaccharide trichloroacetimidate derivative 18 was allowed to

• temperature, 2 h, 98%. Reagents and conditions: (a) Benzoyl chloride, pyridine, 0 °C, 3 h, 75%; (b) Tf2O, BSP, TTBP, CH2Cl2, MS 4 Å, −60 °C, 1 h then compound 10, −78 °C, 2 h, 65%; (c) PdCl2, CH3OH, 0 °C to room temperature, 3 h, 75%; (d) CCl3CN, DBU, CH2Cl2, −10 °C, 90% (mixture of α and β). Reagents and

Sigmatropic rearrangements of cyclopropenylcarbinol derivatives. Access to diversely substituted alkylidenecyclopropanes

• Guillaume Ernouf,
• Jean-Louis Brayer,
• Christophe Meyer and
• Janine Cossy

Beilstein J. Org. Chem. 2019, 15, 333–350, doi:10.3762/bjoc.15.29

• that the amine could play a role in promoting the [2,3]-sigmatropic rearrangement. After a screening of different tertiary amines, Rubin et al. found that DBU could be used as a base in the phosphinylation reaction but also as an efficient catalyst for the subsequent [2,3]-sigmatropic rearrangement of

• diastereoselectivity. However, the sigmatropic rearrangement of the highly hindered di(tert-butyl)phosphinite 6j and tetra(isopropyl) phosphorodiamidite 6k did not occur (Scheme 7) [37]. The mechanism proposed by Rubin et al. involves a reversible addition of the Lewis base (DBU) on the cyclopropene double bond at C2

• ’ would then be obtained and would eventually produce the diastereomeric phosphine oxides 7 and 7’. Computational studies indicated that the facial selectivity of the initial attack of the Lewis base (DBU) was not responsible for the observed diastereocontrol because of the low difference between the

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

• 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

Unexpected loss of stereoselectivity in glycosylation reactions during the synthesis of chondroitin sulfate oligosaccharides

• Teresa Mena-Barragán,
• José L. de Paz and
• Pedro M. Nieto

Beilstein J. Org. Chem. 2019, 15, 137–144, doi:10.3762/bjoc.15.14

• selective formation of the β(1→4) linkage in the [2 + 2] coupling. Cleavage of the anomeric 4-methoxyphenyl group followed by treatment with trichloroacetonitrile and DBU gave glycosyl donor 1 in high yield. For the synthesis of acceptor 2, diol 6 was selectively acylated at position 6 using 1.1 equiv of

• DBU. The glycosylation reaction with 2-propanol using TMSOTf as Lewis acid at 0 ºC cleanly provided the β-isopropyl glycoside 13 in 65% yield. Interestingly, no α-anomer was detected in the reaction mixture. Finally, cleavage of the levulinyl group using hydrazine monohydrate in pyridine/acetic acid

• = pivaloyl; PMP = 4-methoxyphenyl. Reagents and conditions: a) TMSOTf, CH2Cl2, 0 °C, 30 min, 97%; b) (HF)n·Py, THF, 0 °C, 20 h, 90%; c) Ac2O, Py, 24 h, 97%; d) CAN, CH2Cl2/CH3CN/H2O, 0 °C, 1 h, 99%; e) Cl3CCN, DBU, CH2Cl2, 9 h, 98%. CAN = ceric(IV) ammonium nitrate. Reagents and conditions: a

Synthesis of unnatural α-amino esters using ethyl nitroacetate and condensation or cycloaddition reactions

• Glwadys Gagnot,
• Vincent Hervin,
• Eloi P. Coutant,
• Sarah Desmons,
• Racha Baatallah,
• Victor Monnot and
• Yves L. Janin

Beilstein J. Org. Chem. 2018, 14, 2846–2852, doi:10.3762/bjoc.14.263

• , a literature search pointed out the use of an excess of DBU and heat [38][39]. However, boiling compound 40 in toluene in the presence of an excess of DBU led, after chromatography, to only 24% of the benzyl ester 41. Since, amongst few side reactions, we suspected a benzylester cleavage, we

• undertook this reaction under argon in ethanol at 110 °C using a microwave reactor along with only one equivalent of DBU and these changes provided us with the ethyl ester 42 in a 51% yield. Finally, a far more simple procedure was found by just adding a catalytic amount of hydrogen chloride in 1,4-dioxane

DABCO- and DBU-promoted one-pot reaction of N-sulfonyl ketimines with Morita–Baylis–Hillman carbonates: a sequential approach to (2-hydroxyaryl)nicotinate derivatives

• Soumitra Guin,
• Raman Gupta,
• Debashis Majee and
• Sampak Samanta

Beilstein J. Org. Chem. 2018, 14, 2771–2778, doi:10.3762/bjoc.14.254

• Soumitra Guin Raman Gupta Debashis Majee Sampak Samanta Discipline of Chemistry, Indian Institute of Technology Indore, Simrol, Indore, 453552, Madhya Pradesh, India 10.3762/bjoc.14.254 Abstract An intriguing DABCO-catalyzed and DBU-promoted one-pot synthesis of an important class of (2

• cyclic sulfamidate imines and MBH acetates of acrylate as coupling partners [68]. Herein, we further present a DABCO-catalyzed and DBU-promoted sequential one-pot procedure for the access to the interesting class of (2-hydroxyaryl)nicotinates/nicotinonitriles from N-sulfonyl ketimines and MBH adducts as

• ) were obtained when the reaction was conducted at 60 °C (entry 2, Table 1). By increasing the temperature as well as the loading of DABCO (1.0 equiv, entry 3, Table 1), a similar result was observed. At this situation, we surmised that step II may require a stronger base like DBU which will facilitate