Synthesis and characterization of bis(4-amino-2-bromo-6-methoxy)azobenzene derivatives

• David Martínez-López,
• Amirhossein Babalhavaeji,
• Diego Sampedro and
• G. Andrew Woolley

Beilstein J. Org. Chem. 2019, 15, 3000–3008, doi:10.3762/bjoc.15.296

• , resulting in a yellowish oil. This was purified by column chromatography using hexane/ethyl acetate, 4:1, v/v as eluent. The product, phenol tert-butyl (4-chloro-2-hydroxyphenyl)carbamate, was used directly in the next step. (2) tert-Butyl (4-chloro-2-hydroxyphenyl)carbamate (2 mmol, 500 mg) was dissolved

• brown oil. This was poured into water and extracted three times with DCM. The organic fractions were collected and evaporated under reduced pressure. The product, tert-butyl (4-chloro-2-methoxyphenyl)carbamate, was used directly in the next step. (3) tert-Butyl (4-chloro-2-methoxyphenyl)carbamate (400

A review of asymmetric synthetic organic electrochemistry and electrocatalysis: concepts, applications, recent developments and future directions

• Munmun Ghosh,
• Valmik S. Shinde and
• Magnus Rueping

Beilstein J. Org. Chem. 2019, 15, 2710–2746, doi:10.3762/bjoc.15.264

• mepivacaine (197a) [107]. The key steps in the synthesis involved the initial anodic oxidation of cyclic N-carbamate 194 bearing an 8-phenylmenthyl group as a chiral auxiliary which generates in situ N-acyliminium ion 195 and this 195 upon reaction with nucleophilic CN− in presence of catalytic TMSOTf and β

AgNTf₂-catalyzed formal [3 + 2] cycloaddition of ynamides with unprotected isoxazol-5-amines: efficient access to functionalized 5-amino-1H-pyrrole-3-carboxamide derivatives

• Ziping Cao,
• Jiekun Zhu,
• Li Liu,
• Yuanling Pang,
• Laijin Tian,
• Xuejun Sun and
• Xin Meng

Beilstein J. Org. Chem. 2019, 15, 2623–2630, doi:10.3762/bjoc.15.255

• 10ka–na were obtained in 50–98% yields. In addition, the Ts protecting group could be changed for other sulfonyl groups such as Ms (10na, 98%), o-Ns (10oa, 99%) and p-Ns (10pa, 99%), while the cyclic carbamate-derived ynamides such as 4q are no good substrates, leading to the formation of a complex

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

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

• protections, which contained a tertiary butyl carbamate moiety, were not completely stable under the acidic conditions needed for de-tritylation in each synthetic cycle. Once the protection was lost, in the coupling step, incoming phosphoramidites would react with the free amino groups, and branched ODNs

Diaminoterephthalate–α-lipoic acid conjugates with fluorinated residues

• Leon Buschbeck,
• Aleksandra Markovic,
• Gunther Wittstock and
• Jens Christoffers

Beilstein J. Org. Chem. 2019, 15, 981–991, doi:10.3762/bjoc.15.96

• α-lipoic acid (ALA) residue. Furthermore, a fluorine-substituted moiety bound to DAT shall facilitate detection by XPS. Results and Discussion Synthesis. The preparation of DAT–ALA conjugate 3 with a fluorinated residue started from mono-carbamate-protected diethyl DAT 1 (Scheme 1). Compound 1 was

• in [44], TFA (3 mL) was added dropwise to a cooled (ice-water bath) solution of carbamate 2 (0.402 mmol, 205 mg) in CH2Cl2 (3 mL). The mixture was stirred for 19 h at ambient temperature and then poured into saturated aqueous NaHCO3 solution (50 mL). After stirring for 5 min at ambient temperature

• -(trifluoromethyl)benzylamino]terephthalate (8): Under exclusion of air and moisture, morpholine (1.17 mmol, 102 mg, 5.0 equiv) was added to a solution of carbamate 6 (0.234 mmol, 129 mg, 1.0 equiv) in abs. CH2Cl2 (3 mL). The mixture was degassed (three cycles of freeze, pump and thaw). Then Pd(PPh3)4 (12 µmol, 14

New α- and β-cyclodextrin derivatives with cinchona alkaloids used in asymmetric organocatalytic reactions

• Iveta Chena Tichá,
• Simona Hybelbauerová and
• Jindřich Jindřich

Beilstein J. Org. Chem. 2019, 15, 830–839, doi:10.3762/bjoc.15.80

• –Hillman and aldol-type reactions, we focused on their application in the decarboxylative asymmetric allylic amination (AAA) [38] of MBH carbamate 12 affording the product 13 with enantiomeric excesses of up to 75% (Scheme 4). However, compared with the published procedure [38] (up to 97% ee, aromatic

• the decarboxylative asymmetric allylic amination of a Morita–Baylis–Hillman carbamate (10 mol % of catalyst, up to 75% ee, up to 76% isolated yield). We believe that these new CD derivatives comprising cinchona alkaloids will be suitable catalysts of other asymmetric reactions using them under green

• -N3-β-CD (7) and propargylated cinchona alkaloids 3a–d. Synthesis of difunctionalized α-CD 11 with quinine moieties. AAA reaction of MBH carbamate 12 catalyzed by the prepared CD derivatives 4a–d, 5a–d, 8a–d, 9a–d, 11. Optimized conditions of the CuAAC click reactions of non-methylated azido-CDs with

A diastereoselective approach to axially chiral biaryls via electrochemically enabled cyclization cascade

• Hong Yan,
• Zhong-Yi Mao,
• Zhong-Wei Hou,
• Jinshuai Song and
• Hai-Chao Xu

Beilstein J. Org. Chem. 2019, 15, 795–800, doi:10.3762/bjoc.15.76

• imidazopyridine-containing biaryls via central-to-axial chirality transfer (Scheme 1). Results and Discussion The substituents on the phenyl ring (R1) and at the propargylic position (R2) of carbamate 2 were varied to study their effects on the diastereoselectivity (Table 1). The electrolysis was conducted under

• Et4NBF4 (1 equiv) as the supporting electrolyte. These investigations indicated that bulky tertiary groups at both R1 and R2 positions were needed to ensure efficient chirality transfer. Hence, carbamate 2a (Table 1, entry 1) bearing a t-Bu group at R1 and R2 positions, respectively, reacted to give

• the electrosynthesis was investigated by varying the peripheral substituents of the carbamate substrate 2 (Scheme 2). The pyridyl ring could be substituted at positions 4, 5 and 6 with a range of substituents with diverse electronic properties such as OMe (3e), Br (3f), CF3 (3g), CN (3h), Cl (3i), and

Cyclopropene derivatives of aminosugars for metabolic glycoengineering

• Jessica Hassenrück and
• Valentin Wittmann

Beilstein J. Org. Chem. 2019, 15, 584–601, doi:10.3762/bjoc.15.54

• and their suitability for MGE. Three mannosamine derivatives in which the cyclopropene moiety is attached to the sugar by either an amide or a carbamate linkage and that differ by the presence or absence of a stabilizing methyl group at the double bond have been examined. We determined their DAinv

• conditions. From these experiments, it became obvious that N-(cycloprop-2-en-1-ylcarbonyl)-modified (Cp-modified) mannosamine has the highest metabolic acceptance. However, carbamate-linked N-(2-methylcycloprop-2-en-1-ylmethyloxycarbonyl)-modified (Cyoc-modified) mannosamine despite its lower metabolic

• amide [18], carbamate [19], or most recently a urea linkage [20] have been reported. Terminal alkenes are small which is beneficial for being accepted by the enzymes involved in glycan biosynthesis. However, they react only slowly in the DAinv reaction [20]. In contrast, ring-strained alkenes, such as

LCST phase behavior of benzo-21-crown-7 with different alkyl chains

• Yan Deng,
• Xing Li,
• Qiao Zhang,
• Zheng Luo,
• Chengyou Han and
• Shengyi Dong

Beilstein J. Org. Chem. 2019, 15, 437–444, doi:10.3762/bjoc.15.38

• and molecular structures. Results and Discussion Two series of B21C7s, comprising carbamate-based linkers 3a–e and urea-based linkers 5a–e, were designed and synthesized, as shown in Scheme 1 and Scheme 2. All structures were confirmed by NMR spectroscopy and high-resolution mass spectrometry (details

• between the amine groups and isocyanate units (yields, 44.6–76.5%), or between hydroxy groups and isocyanate units (yields, 57.4–84.9%), respectively. We also investigated the role of linkages in LCST behavior by the introduction of urea-based and carbamate-based linkers. The water solubility of the

• ethers with urea-based linkers show higher water solubility (5a–e), compared to crown ethers with carbamate-based linkers (3a–e). As amide groups are more hydrophilic compared with ester groups, it is reasonable that 5a–e show stronger hydration effects and exhibit a larger water-accessible surface area

Tandem copper and photoredox catalysis in photocatalytic alkene difunctionalization reactions

• Nicholas L. Reed,
• Madeline I. Herman,
• Vladimir P. Miltchev and
• Tehshik P. Yoon

Beilstein J. Org. Chem. 2019, 15, 351–356, doi:10.3762/bjoc.15.30

• describe a method for alkene oxyamination and diamination that utilizes simple carbamate and urea groups as nucleophilic heteroatom donors. This method uses a tandem copper–photoredox catalyst system that is operationally convenient. The identity of the terminal oxidant is critical in these studies. Ag(I

• of carbamate 1 (Table 1), a reaction we had previously studied under stoichiometric Cu(II) conditions and found to proceed in good yield using 2.5 mol % 2,4,6-triphenylpyrylium tetrafluoroborate (TPPT, 3) as a photocatalyst and 1.2 equiv of Cu(TFA)2 as a stoichiometric oxidant. We lowered the loading

• tether (15) did not adversely affect the reaction. Intermolecular oxyamination of styrenes is also feasible using these conditions. While simple styrenes polymerize rapidly under these conditions, a range of β-substituted styrenes undergo smooth oxyamination using tert-butyl carbamate as the nucleophilic

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

• -disubstitution at C3 on the three-membered ring. Alcohol 25 was readily converted to carbamate 26 by reaction with trichloroacetyl isocyanate followed by cleavage of the trichloroacetyl group by alkaline hydrolysis. Dehydration of carbamate 26 was achieved by treatment with trifluoroacetic anhydride in the

• at 40 °C but could be accelerated by addition of Ti(OiPr)4 (10 mol %) to deliver the corresponding N-Boc- carbamate 36 (81%). The condensation of isocyanate 28 with N-Boc-glycine in the presence of DMAP (Goldschmidt–Wick coupling) [57] provided amide 37 in 70% yield (Scheme 16) [53]. The examination

• ) arising from the [3,3]-sigmatropic rearrangement of cyclopropenylcarbinyl cyanates could also be derivatized into trifluoroacetamides. This transformation was discovered fortuitously when carbamate 49 was treated with an excess of trifluoroacetic anhydride (2 equiv) in the presence of Et3N (3 equiv) to

Silanediol versus chlorosilanol: hydrolyses and hydrogen-bonding catalyses with fenchole-based silanes

• Falco Fox,
• Jörg M. Neudörfl and
• Bernd Goldfuss

Beilstein J. Org. Chem. 2019, 15, 167–186, doi:10.3762/bjoc.15.17

• ion catalyses The N-acyl Mannich reaction of isochinolin (16), which is activated with 2,2,2-trichloroethoxycarbonyl chloride (17, TrocCl) to carbamate 10, and different silyl ketene acetals 11a–d yielding product 12 (Scheme 6) [45][47], is studied. Mattson et al. proposed a mechanism where the

Stereodivergent approach in the protected glycal synthesis of L-vancosamine, L-saccharosamine, L-daunosamine and L-ristosamine involving a ring-closing metathesis step

• Pierre-Antoine Nocquet,
• Aurélie Macé,
• Frédéric Legros,
• Jacques Lebreton,
• Gilles Dujardin,
• Sylvain Collet,
• Arnaud Martel,
• Bertrand Carboni and
• François Carreaux

Beilstein J. Org. Chem. 2018, 14, 2949–2955, doi:10.3762/bjoc.14.274

• speculated that the cyclic vinyl ether derivative I, with the prerequisite configuration of all stereogenic centers of the carbamate-protected glycal of L-vancosamine 1, could be obtained from the alcohol derivative II using an O-vinylation–ring-closing metathesis sequence (Figure 3). Afterwards, the

• diastereoisomer, the carbamate-protected 3-aminoglycal of L-saccharosamine 2, employing the (S)-(−)-methyl lactate as common starting material. The efficiency and generality of this methodology was also demonstrated by a new synthesis of C-3 unbranched amino glycals, L-daunosamine 3 and L-ristosamine 4

• synthesis of the carbamate-protected glycal of L-vancosamine 1 and L-saccharosamine 2 were prepared in two steps by treatment of alcohols with the trichloroacetyl isocyanate reagent (TCA-NCO) followed by basic hydrolysis. The spectroscopic properties of carbamates 17 were identical to those reported in the

Ring-opening metathesis of some strained bicyclic systems; stereocontrolled access to diolefinated saturated heterocycles with multiple stereogenic centers

• Zsanett Benke,
• Melinda Nonn,
• Márton Kardos,
• Santos Fustero and
• Loránd Kiss

Beilstein J. Org. Chem. 2018, 14, 2698–2707, doi:10.3762/bjoc.14.247

• gel (n-hexane/EtOAc). Characterization of the synthesized substances tert-Butyl ((S*)-1-((3R*,5S*)-2-oxo-5-vinyltetrahydrofuran-3-yl)allyl)carbamate ((±)-5). Yellow oil; yield 25%; Rf 0.70 (n-hexane/EtOAc 2:1); 1H NMR (CDCl3, 400 MHz) δ 1.41 (s, 9H, t-Bu), 1.82–1.88 (m, 1H, CH2), 2.40–2.47 (m, 1H

• C14H21NO4: C, 62.90; H, 7.92; N, 5.24; found, C, 62.55; H, 7.58; N, 4.89. tert-Butyl ((R*)-1-((3R*,5S*)-2-oxo-5-vinyltetrahydrofuran-3-yl)allyl)carbamate ((±)-6). Yellow oil; yield 36%; Rf 0.72 (n-hexane/EtOAc 2:1); 1H NMR (CDCl3, 400 MHz) δ 1.47 (s, 9H, t-Bu), 1.94–1.99 (m, 1H, CH2), 2.46–2.51 (m, 1H, CH2

• ]; anal. calcd for C14H21NO4: C, 62.90; H, 7.92; N, 5.24; found, C, 62.59; H, 8.30; N, 4.87. tert-Butyl ((2S*,3R*,4R*)-4-allyl-5-oxo-2-vinyltetrahydrofuran-3-yl)carbamate ((±)-10). Yellow oil; yield 35%; Rf 0.70 (n-hexane/EtOAc 2:1); 1H NMR (CDCl3, 400 MHz) δ 1.48 (s, 9H, t-Bu), 2.42–2.49 (m, 1H, CH2

Cobalt- and rhodium-catalyzed carboxylation using carbon dioxide as the C1 source

• Tetsuaki Fujihara and
• Yasushi Tsuji

Beilstein J. Org. Chem. 2018, 14, 2435–2460, doi:10.3762/bjoc.14.221

• coumarin derivatives were obtained in moderate-to-good yields. Notably, ketone (24e), ester (24d) moieties were tolerated in the reaction. In addition, 2-quinolones (24f and 24g) were obtained using alkynes bearing a Boc protected carbamate in place of the MOM protected ether. Scheme 23 shows a plausible

Synthesis of 1,4-imino-L-lyxitols modified at C-5 and their evaluation as inhibitors of GH38 α-mannosidases

• Maroš Bella,
• Sergej Šesták,
• Ján Moncoľ,
• Miroslav Koóš and
• Monika Poláková

Beilstein J. Org. Chem. 2018, 14, 2156–2162, doi:10.3762/bjoc.14.189

• attempts resulted in either no reaction or formation of an unstable mesylate. For this reason, the inversion of configuration was performed by the activation of the hydroxy group in 18 with triflic anhydride in the presence of pyridine at 0 °C to form carbamate 20 in 72% yield (Scheme 4). The structure and

• absolute configuration of carbamate 20 was confirmed by single-crystal X-ray analysis (Figure 2) [36]. Basic hydrolysis of carbamate 20 with 10% NaOH in refluxing EtOH provided aminoalcohol 21 which was subsequently N-benzylated with the corresponding benzyl bromides to yield pyrrolidines 22. Final

Cationic cobalt-catalyzed [1,3]-rearrangement of N-alkoxycarbonyloxyanilines

• Itaru Nakamura,
• Mao Owada,
• Takeru Jo and
• Masahiro Terada

Beilstein J. Org. Chem. 2018, 14, 1972–1979, doi:10.3762/bjoc.14.172

• recovery of the starting material 1a (Table 2, entries 8–10). A protic solvent, such as methanol, was ineffective (Table 2, entry 11). Slight dilution of the reaction solution (0.25 M) improved the chemical yield (Table 2, entry 12). As mentioned previously [13], carbamate-type groups, such as

An amine protecting group deprotectable under nearly neutral oxidative conditions

• Shahien Shahsavari,
• Chase McNamara,
• Mark Sylvester,
• Emily Bromley,
• Savannah Joslin,
• Bao-Yuan Lu and
• Shiyue Fang

Beilstein J. Org. Chem. 2018, 14, 1750–1757, doi:10.3762/bjoc.14.149

• collection of transformations to be carried out on the protected substrates that are unattainable using any known protecting groups. Keywords: amine; carbamate; dM-Dmoc; oxidation; protecting group; Introduction In multistep organic synthesis, amino groups usually have to be protected [1]. Protecting

• carbamate and 6-nitroveratryl carbamate) [9][10] and fluoride (e.g., trimethylsilylethyloxycarbonyl (Teoc) group) [11][12]. The 1,3-dithian-2-ylmethoxycarbonyl (Dmoc) group first reported by Kunz and co-workers provides a different dimension of orthogonality of amine protection in terms of deprotection

• experimental section). The compound is stable, which allows easy purification and storage. However, we expected that it could react with amines under suitable conditions. Using benzylamine (3a) as the model substrate, we tested a variety of reaction conditions to form the dM-Dmoc protected carbamate 5a (see

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

• conjugation of the novel cryptophycin analogues across an appropriate linker to an antibody or peptide. Either a virtually uncleavable triazole (introduced by CuAAC) or scissile ester, carbonate, or carbamate moieties were taken into account. The synthesis of the modified unit B (Scheme 1) started with the

London dispersion as important factor for the stabilization of (Z)-azobenzenes in the presence of hydrogen bonding

• Andreas H. Heindl,
• Raffael C. Wende and
• Hermann A. Wegner

Beilstein J. Org. Chem. 2018, 14, 1238–1243, doi:10.3762/bjoc.14.106

• isomerization rates of several N-substituted 4,4′-bis(4-aminobenzyl)azobenzenes were measured. An intramolecular stabilization was observed and explained by the interplay of intramolecular amide and carbamate hydrogen bonds as well as London dispersion interactions. Whereas in toluene, 1,4-dioxane and tert

• amide [34]. This explains the highest stabilization of the trimethylhexanoylamide 4 (experimentally and computationally), followed by the tert-butylamide 5 and tert-butyl carbamate 6, which are almost equally stabilized. Nevertheless, hydrogen bonds are strongly dependent on the solvent system and

An overview of recent advances in duplex DNA recognition by small molecules

• Sayantan Bhaduri,
• Nihar Ranjan and
• Dev P. Arya

Beilstein J. Org. Chem. 2018, 14, 1051–1086, doi:10.3762/bjoc.14.93

On the design principles of peptide–drug conjugates for targeted drug delivery to the malignant tumor site

• Eirinaios I. Vrettos,
• Gábor Mező and
• Andreas G. Tzakos

Beilstein J. Org. Chem. 2018, 14, 930–954, doi:10.3762/bjoc.14.80

• unit (EHU; colored in green) and to a tumor-targeting element (i.e. tumor homing peptide; colored in black). The alcohol group at the opposite site can be connected via a carbonate ester/carbamate bond to the cytotoxic agent (colored in blue). The EHU is designed so as to be a substrate for proteases

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

• between heteroaryl bromides, chlorides or iodides and carbamate, sulfonamide or urea derivatives to be successfully realized in water using palladium-loaded TPGS-750-M (dl-α-tocopherol methoxypolyethylene glycol succinate) micelles (Scheme 1). Moreover, this micellar catalytic system allowed for catalyst