Efficient synthesis of dipeptide analogues of α-fluorinated β-aminophosphonates

• Marcin Kaźmierczak and
• Henryk Koroniak

Beilstein J. Org. Chem. 2020, 16, 756–762, doi:10.3762/bjoc.16.69

• fluorination reactions with these reagents require the use of a base as an activator [20]. Doyle demonstrated the combination between PyFluor or PBSF and bases such as 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU, 6), 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene (MTBD, 7), 2-tert-butyl-1,1,3,3-tetramethylguanidine

•  2, for all tested conditions see Table S1 in Supporting Information File 1). In our experience, there was no significant correlation between steric bulkiness of the base (from DBU to BTPP) used, and the yield of α-isomer 11 formation. It is worth mentioning that application of PBSF gives slightly

Synthesis of C₇₀-fragment buckybowls bearing alkoxy substituents

• Yumi Yakiyama,
• Shota Hishikawa and
• Hidehiro Sakurai

Beilstein J. Org. Chem. 2020, 16, 681–690, doi:10.3762/bjoc.16.66

• using 20 mol % of Pd(PPh3)2Cl2 and 150 mol % DBU in DMF at 150 °C under microwave irradiation conditions to afford the desired dimethoxy derivative 5a in 75% yield. In contrast, when the reaction of 4b was performed, not only the desired product 5b but also the unexpected regioisomer 5c was obtained

• described in [18], in a glove box to the microwave vial was added 4 (0.030 mmol), Pd(PPh3)2Cl2 (6.0 μmol), and degassed DMF (3 mL) and prior sealing the vial DBU (6.7 μL, 0.045 mmol) and the mixture was stirred for 40 min at 150 °C using microwave. After the addition of ethyl acetate/hexane, the mixture was

Microwave-assisted efficient and facile synthesis of tetramic acid derivatives via a one-pot post-Ugi cascade reaction

• Yong Li,
• Zheng Huang,
• Jia Xu,
• Yong Ding,
• Dian-Yong Tang,
• Jie Lei,
• Hong-yu Li,
• Zhong-Zhu Chen and
• Zhi-Gang Xu

Beilstein J. Org. Chem. 2020, 16, 663–669, doi:10.3762/bjoc.16.63

• developed through an Ugi/Dieckmann cyclization strategy with DBU. This two-step one-pot procedure afforded the targeted tetramic acid analogues in good yields. With commercially available Ugi starting materials, microwave irradiation, a simple operation, excellent yields, and a broad scope, this reaction

• ) failed to afford comparable or better yields. However, when DBU, an organic base, was used, the yield of 7a was significantly increased (Table 1, entry 6). We then investigated the effect of solvent and temperature for the reaction. The results tested in different solvent systems were summarized in Table

• then DBU (1.0 mmol) was added. The mixture was then placed in a microwave synthesizer and heated to 120 °C for 10 min. The mixture was then cooled to room temperature, and the residue was dissolved in EtOAc (15.0 mL). The solution was washed with brine, and the organic layer was dried with MgSO4 and

Cascade trifluoromethylthiolation and cyclization of N-[(3-aryl)propioloyl]indoles

• Ming-Xi Bi,
• Shuai Liu,
• Yangen Huang,
• Xiu-Hua Xu and
• Feng-Ling Qing

Beilstein J. Org. Chem. 2020, 16, 657–662, doi:10.3762/bjoc.16.62

• slightly higher yields, respectively (Table 1, entries 3 and 4). Switching KHCO3 to NaHCO3 could enhance the yield (Table 1, entry 6), whereas K2CO3 and DBU reduced the reaction efficiency (Table 1, entries 5 and 7). Subsequent evaluation of solvents revealed that MeCN and DMF were inferior to DMSO (Table

Rhodium-catalyzed reductive carbonylation of aryl iodides to arylaldehydes with syngas

• Zhenghui Liu,
• Peng Wang,
• Zhenzhong Yan,
• Suqing Chen,
• Dongkun Yu,
• Xinhui Zhao and
• Tiancheng Mu

Beilstein J. Org. Chem. 2020, 16, 645–656, doi:10.3762/bjoc.16.61

• , triphos, dpp-BINAP, dpp-OPh, dppb, dppe, P(PhF5)3, P(4-FPh)3, Cydpp, Bipy, DBU, Im, and PPh3 (their structures are shown in Table 2)), bases (Et3N, 1,4-diaza[2.2.2]bicyclooctane (DABCO), N,N-diisopropylethylamine (DIPEA), N,N,N',N'-tetramethylethylenediamine (TMEDA) and 1,2,2,6,6-pentamethylpiperidine

Preparation and in situ use of unstable N-alkyl α-diazo-γ-butyrolactams in Rh^II-catalyzed X–H insertion reactions

• Maria Eremeyeva,
• Daniil Zhukovsky,
• Dmitry Dar’in and
• Mikhail Krasavin

Beilstein J. Org. Chem. 2020, 16, 607–610, doi:10.3762/bjoc.16.55

• -ethoxalyl-γ-lactams 6a–c, prepared by oxalylation of the respective γ-lactams as decribed previously [1], underwent a rapid diazo transfer reaction via the conventional protocol [4][5] employing 4-nitrobenzenesulfonyl azide and DBU. A quick filtration through a plug of alumina (in lieu of silica gel, which

A systematic review on silica-, carbon-, and magnetic materials-supported copper species as efficient heterogeneous nanocatalysts in “click” reactions

• Pezhman Shiri and
• Jasem Aboonajmi

Beilstein J. Org. Chem. 2020, 16, 551–586, doi:10.3762/bjoc.16.52

Exploring the scope of DBU-promoted amidations of 7-methoxycarbonylpterin

• Anna R. Bockman and
• Jeffrey M. Pruet

Beilstein J. Org. Chem. 2020, 16, 509–514, doi:10.3762/bjoc.16.46

• relevant pteridine derivatives. Reactions which expedite the development of new pterins are thus of great importance. Through a dual role of diazabicycloundecene (DBU), 7-carboxymethylpterin is converted to the soluble DBU salt, with additional DBU promoting an ester-to-amide transformation. We have

• yields often >80%. Keywords: amidation; DBU; folate; pterin; Introduction Pteridines are a class of fused bicyclic heterocycles with significant biological relevance. The 2-amino-4-pteridinone core, simply referred to as “pterin”, is present in various biological cofactors like folates, biopterin, and

• new pterins. As such, any reaction which expedites the synthesis of pterin derivatives, especially those which bypass the insolubility, is of great importance to both medicinal and supramolecular chemists. We first reported the application of DBU as a crucial additive in the synthesis of pterins used

Synthesis of 4-amino-5-fluoropyrimidines and 5-amino-4-fluoropyrazoles from a β-fluoroenolate salt

• Tobias Lucas,
• Jule-Philipp Dietz and
• Till Opatz

Beilstein J. Org. Chem. 2020, 16, 445–450, doi:10.3762/bjoc.16.41

• investigate the use of non-nucleophilic bases, but with DBU, polymerization of the fluoroenolate took place. When using aqueous sodium hydroxide as the base, a 19% yield could be achieved. Switching the solvent to water led to an improvement of the yield to 36% (Table 2). In water, but without using a base

Oligomeric ricinoleic acid preparation promoted by an efficient and recoverable Brønsted acidic ionic liquid

• Fei You,
• Xing He,
• Song Gao,
• Hong-Ru Li and
• Liang-Nian He

Beilstein J. Org. Chem. 2020, 16, 351–361, doi:10.3762/bjoc.16.34

• mol (15.2 g) 1,8-diazobicyclo[5,4,0]undec-7-ene (DBU) in a flask containing 50 mL of acetonitrile. After 24 h reflux at 80 °C, the reaction mixture was cooled to room temperature. Then 30 mL diethyl ether was added to the reaction mixture to precipitate the product. After that, the precipitate was

Copper-catalyzed enantioselective conjugate addition of organometallic reagents to challenging Michael acceptors

• Delphine Pichon,
• Jennifer Morvan,
• Christophe Crévisy and
• Marc Mauduit

Beilstein J. Org. Chem. 2020, 16, 212–232, doi:10.3762/bjoc.16.24

• protocol failed in the case of linear dienoates [29]. Interestingly, after a subsequent reconjugation step in the presence of DBU, the resulting enantioenriched γ-methylated α,β-unsaturated thioester 18a was subsequently reacted in a 1,4-ECA reaction catalyzed by Josiphos (L9)/CuBr·SMe2. Using both

The reaction of arylmethyl isocyanides and arylmethylamines with xanthate esters: a facile and unexpected synthesis of carbamothioates

• Narasimhamurthy Rajeev,
• Toreshettahally R. Swaroop,
• Ahmad I. Alrawashdeh,
• Shofiur Rahman,
• Abdullah Alodhayb,
• Seegehalli M. Anil,
• Kuppalli R. Kiran,
• Chandra,
• Paris E. Georghiou,
• Kanchugarakoppal S. Rangappa and
• Maralinganadoddi P. Sadashiva

Beilstein J. Org. Chem. 2020, 16, 159–167, doi:10.3762/bjoc.16.18

• solvents, such as THF, acetonitrile, dioxane, DMSO, or toluene, in the presence of sodium hydride, none of these reactions afforded the product 4a in a satisfactory yield (Table 1, method A, entries 2–6). Replacement of sodium hydride by DBU did not furnish any product at all (Table 1, method A, entry 7

• ) dithiocarbonate (1f) also afforded the corresponding carbamothioates 4k and 4l in 82% and 88% yields, with benzyl isocyanide (2a) and 4-fluorobenzyl isocyanide (2c), respectively. The use of a weaker base, such as DBU, failed to form any product (Table 1, methods A and B, entry 7). For the purpose of comparison

Regioselectivity of glycosylation reactions of galactose acceptors: an experimental and theoretical study

• Enrique A. Del Vigo,
• Carlos A. Stortz and
• Carla Marino

Beilstein J. Org. Chem. 2019, 15, 2982–2989, doi:10.3762/bjoc.15.294

• byproduct [25]. Glycosylation reactions With acceptors 1α/β and 2α/β in hand, we assayed the glycosylation reactions of glycosyl donors 3–5. Trichloroacetimidates 3 [26] and 4 [27] were prepared by treatment of the corresponding benzoylated hemiacetals with trichloroacetonitrile and DBU, as previously

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