Nucleofugal behavior of a β-shielded α-cyanovinyl carbanion

• Rudolf Knorr and
• Barbara Schmidt

Beilstein J. Org. Chem. 2018, 14, 3018–3024, doi:10.3762/bjoc.14.281

• performed with methyllithium or methylmagnesium bromide and gas-volumetric control of the liberated methane (ca. 25 mL/mmol at 22 °C). All 1H and 13C NMR shifts δ were referenced with internal Me4Si. NMR abbreviations were as follows: d = doublet, m = multiplet, q = quartet, quat = quaternary, s = singlet

Generation of 1,2-oxathiolium ions from (arysulfonyl)- and (arylsulfinyl)allenes in Brønsted acids. NMR and DFT study of these cations and their reactions

• Stanislav V. Lozovskiy,
• Alexander Yu. Ivanov,
• Olesya V. Khoroshilova and
• Aleksander V. Vasilyev

Beilstein J. Org. Chem. 2018, 14, 2897–2906, doi:10.3762/bjoc.14.268

• large positive charge in cations A, B. For dication Bh, different signals were detected for quaternary carbons C5 and C5', and vinyl carbons C4 and C4', etc., that, probably, indicates formation of two diastereomers (one meso-form and one pair of enantiomers) due to the stereogenic sulfur centers. In

The influence of the cationic carbenes on the initiation kinetics of ruthenium-based metathesis catalysts; a DFT study

• Magdalena Jawiczuk,
• Angelika Janaszkiewicz and
• Bartosz Trzaskowski

Beilstein J. Org. Chem. 2018, 14, 2872–2880, doi:10.3762/bjoc.14.266

• stable in water and, therefore, environmentally-friendly. The idea of incorporating a quaternary ammonium moiety into the imidazole part of the carbene was later expanded by several other groups, including a number of new water-soluble catalysts synthesized by Skowerski et al. [23][24]. In the meantime

• computational accuracy of our protocol. To justify the lack of influence of the position of the quaternary amine on the Gibbs free energies of initiation we decided to perform a detailed analysis of partial charges of these systems, as well as complexes 1–3-GrI (Table 5). Interestingly both natural partial

• catalysts synthesized up to date the rational design of new catalysts remains a non-trivial task. To gain general insight into the structure–activity relationship for this class of compounds we computationally investigated three different carbenes bearing a formal +1 charge, in form of quaternary amine, and

Transition metal-free oxidative and deoxygenative C–H/C–Li cross-couplings of 2H-imidazole 1-oxides with carboranyl lithium as an efficient synthetic approach to azaheterocyclic carboranes

• Lidia A. Smyshliaeva,
• Mikhail V. Varaksin,
• Pavel A. Slepukhin,
• Oleg N. Chupakhin and
• Valery N. Charushin

Beilstein J. Org. Chem. 2018, 14, 2618–2626, doi:10.3762/bjoc.14.240

• resonances of 2H-imidazole methyl (δ 24.06 ppm) and ethyl (δ 6.74 and 31.12 ppm) groups. In addition, the interaction observed in the HMBC spectra of quaternary carbons with protons of methyl and ethyl groups through the long-range constants allows the signal at δ 103.85 ppm in the 13C NMR spectra of 5d to

Synthesis of cis-hydrindan-2,4-diones bearing an all-carbon quaternary center by a Danheiser annulation

• Gisela V. Saborit,
• Carlos Cativiela,
• Ana I. Jiménez,
• Josep Bonjoch and
• Ben Bradshaw

Beilstein J. Org. Chem. 2018, 14, 2597–2601, doi:10.3762/bjoc.14.237

• relative configuration of the major epimer of 8 (Figure 3) was established on the basis of a cross peak in the NOESY spectrum that correlated the methyl group at C3 with a methylene proton adjacent to the quaternary carbon of the side chain at C3a. The configuration at C3, adjacent to a carbonyl group, is

Synthesis of 3-aminocoumarin-N-benzylpyridinium conjugates with nanomolar inhibitory activity against acetylcholinesterase

• Nisachon Khunnawutmanotham,
• Cherdchai Laongthipparos,
• Patchreenart Saparpakorn,
• Nitirat Chimnoi and
• Supanna Techasakul

Beilstein J. Org. Chem. 2018, 14, 2545–2552, doi:10.3762/bjoc.14.231

• domains. A catalytic triad (CT) that comprises Ser203, His447, and Glu334 residues is responsible for hydrolyzing the ester bond of ACh [20]. The CAS, which is responsible for the binding of the quaternary ammonium moiety of choline, consists of Trp86, Tyr133, Tyr337, and Phe338 [21]. The acyl pocket

Calixazulenes: azulene-based calixarene analogues – an overview and recent supramolecular complexation studies

• Paris E. Georghiou,
• Shofiur Rahman,
• Abdullah Alodhayb,
• Hidetaka Nishimura,
• Jaehyun Lee,
• Atsushi Wakamiya and
• Lawrence T. Scott

Beilstein J. Org. Chem. 2018, 14, 2488–2494, doi:10.3762/bjoc.14.225

• . Table 1 also shows the average values of the calculated distances between the quaternary nitrogen atom and the “deepest” carbon atoms (i.e., C-1) in each of the azulenes in the calix[4]azulene bowls. A small trend can be discerned for the halide salt complexes which is opposite to the trend in the

• measured apparent binding constants. For the tetrafluoroborate salts, however, the trend of the corresponding average quaternary nitrogen-to-carbon distances are in the opposite direction, which is consistent with the increasing sizes of the alkyl groups n-Bu > Et > Me. Clearly, the BF4 salts show less

Non-metal-templated approaches to bis(borane) derivatives of macrocyclic dibridgehead diphosphines via alkene metathesis

• Tobias Fiedler,
• Michał Barbasiewicz,
• Michael Stollenz and
• John A. Gladysz

Beilstein J. Org. Chem. 2018, 14, 2354–2365, doi:10.3762/bjoc.14.211

• dialkyl effect associated with the quaternary centers [52]. Finally, it should be noted that a number of alkene containing phosphine boranes have been employed in metathesis reactions [53][54]. In particular, the tetraalkenyl diphosphine diborane 19·2BH3 in Scheme 10 represents a downsized version of 11

A novel and practical asymmetric synthesis of eptazocine hydrobromide

• Ruipeng Li,
• Zhenren Liu,
• Liang Chen,
• Jing Pan,
• Kuaile Lin and
• Weicheng Zhou

Beilstein J. Org. Chem. 2018, 14, 2340–2347, doi:10.3762/bjoc.14.209

• and methallyl iodide [10]. However, these methods were undermined by expensive reagents, poor yields, harsh reaction conditions, or complex synthetic procedures. Phase-transfer asymmetric catalysis using cinchona alkaloid-derived quaternary ammonium salts is a practical method in organic synthesis [11

Synthesis of spirocyclic scaffolds using hypervalent iodine reagents

• Fateh V. Singh,
• Priyanka B. Kole,
• Saeesh R. Mangaonkar and
• Samata E. Shetgaonkar

Beilstein J. Org. Chem. 2018, 14, 1778–1805, doi:10.3762/bjoc.14.152

• TAN1251A, TAN1251C and TAN1251D [86]. Wardrop and Burge [87] reported a iodine(III)-mediated oxidative spirocyclization of hydroxamates 50. The azaspirans 51 containing quaternary carbon centers were synthesized in good to excellent yields on treating substrates 50 with PIFA (31) in dichloromethane

Design, synthesis and structure of novel G-2 melamine-based dendrimers incorporating 4-(n-octyloxy)aniline as a peripheral unit

• Cristina Morar,
• Pedro Lameiras,
• Attila Bende,
• Gabriel Katona,
• Emese Gál and
• Mircea Darabantu

Beilstein J. Org. Chem. 2018, 14, 1704–1722, doi:10.3762/bjoc.14.145

• amides [64], no such vicinal effect created by a quaternary EWG of type >Nsp3H2+ [63] was detected in the piperazine P-1 linker of compounds 7b, 8 and 9, even in the case of the strongest proton donor, the trimesic acid (pKa = 3.12, 3.89 and 4.70). In addition, only in G-1 amino-dendron D-N

  NH the 1H

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

• provided the optimal reaction outcome. However, they also encountered a problem: the reduced solubility of substrate in the solvent system resulted in lower yields. They therefore examined mixed nitrile solvents again, and eventually found that a quaternary solvent mixture composed of 6:1:1:1 CH2Cl2

A conformationally adaptive macrocycle: conformational complexity and host–guest chemistry of zorb[4]arene

• Liu-Pan Yang,
• Song-Bo Lu,
• Arto Valkonen,
• Fangfang Pan,
• Kari Rissanen and
• Wei Jiang

Beilstein J. Org. Chem. 2018, 14, 1570–1577, doi:10.3762/bjoc.14.134

• wide range of organic cations [32]. ZB4 is also a conformationally adaptive macrocycle. We wondered whether ZB4 has a wide guest binding scope. It was reported that quaternary ammonium-based organic cations (1+–3+) can be hosted by zorb[4]arenes [37][38]. Quaternary ammonium cations 4+ and 5+ and other

• types of organic cations hosted by TA4 (6+–10+) were tested with ZB4. Most of these guests can indeed be complexed. But there are some exceptions. Changing the core quaternary ammonium structure of 3+ completely shuts down the binding, because no obvious complexation-induced shifts were detected in the

• 1:1 mixture of ZB4 with 4+ or 5+ (Figures S1 and S2 in Supporting Information File 1). This indicates the importance of the core quaternary ammonium ions in the host−guest complexation. All other guests can be encapsulated in the cavity of ZB4, and significant chemical shifts on both the guests and

Hyper-reticulated calixarene polymers: a new example of entirely synthetic nanosponge materials

• Alberto Spinella,
• Marco Russo,
• Antonella Di Vincenzo,
• Delia Chillura Martino and
• Paolo Lo Meo

Beilstein J. Org. Chem. 2018, 14, 1498–1507, doi:10.3762/bjoc.14.127

• constituted by the superimposition of different peaks. This can be cumulatively attributed to the C atoms of the tert-butyl groups (both primary and quaternary), the methylene linkers of the calixarene scaffold and, for CaNS1–CaNS3, to the secondary C atoms of the -R- moiety of linker (i.e., the methylene

• quaternary C atoms, respectively. All the spectra also show two other main signals at ca. 51 ± 3 ppm and 67.1 ± 0.2 ppm. The first one can be attributed to the methylene C atoms directly bound to the N1 atom of the triazole ring; its actual position varies significantly depending on the structure of the

Two new 2-alkylquinolones, inhibitory to the fish skin ulcer pathogen Tenacibaculum maritimum, produced by a rhizobacterium of the genus Burkholderia sp.

• Dandan Li,
• Naoya Oku,
• Atsumi Hasada,
• Masafumi Shimizu and
• Yasuhiro Igarashi

Beilstein J. Org. Chem. 2018, 14, 1446–1451, doi:10.3762/bjoc.14.122

• /22.6, and 1.30/31.7), and a methyl (δH/δC 0.89/14.1) group, leaving one carbonyl (δC 179.0) and three aromatic resonances (δC 149.9, 139.4, and 125.3) as quaternary carbons (Table 1). Because these structural elements accounted for six out of eight degrees of unsaturation, the remaining two degrees

Enantioselective phase-transfer catalyzed alkylation of 1-methyl-7-methoxy-2-tetralone: an effective route to dezocine

• Ruipeng Li,
• Zhenren Liu,
• Liang Chen,
• Jing Pan and
• Weicheng Zhou

Beilstein J. Org. Chem. 2018, 14, 1421–1427, doi:10.3762/bjoc.14.119

• separated by two times of resolution with L-tartaric acid and D-tartaric acid (Scheme 1). Phase-transfer asymmetric catalysis with cinchona alkaloid-derived quaternary ammonium compounds has become one of the topics in stereoselective synthesis in both industry and academia [6][7][8][9]. It was reported [10

• to make the process efficient. Results and Discussion A series of the quaternary ammonium bromides from cinchonidine or quinine as phase-transfer catalysts was prepared (Scheme 2). Cinchonidine was reacted with the benzyl bromides (R1Br) in THF to obtain catalysts C1–C11 [13]. And then C7 reacted

• in C7 was crucial to guarantee the stereoselectivity. Meanwhile, the good catalysis was maintained with both dihydrocinchonidine-derived C14 and dehydro compound C15. Finally, the quaternary ammonium group from quinine was examined (Table 1, entries 16 and 17), and C16 and C17 gave the result

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

• -opening reaction. Review Phase-transfer catalysis For the past three decades, asymmetric phase-transfer catalysis utilizing chiral quaternary ammonium salts has attracted great interest as a synthetic strategy since it provides quick access to a large number of enantiopure compounds employing only

• catalytic amounts of chiral phase-transfer agents [32][33][34]. Although the literature contains examples of calixarene derivatives used as phase-transfer catalysts (PTCs) [35], the first asymmetric quaternary ammonium salts derived from cinchona alkaloids based on the calixarene skeleton were prepared by

• chiral calix[4]arenes (±)-1 and (±)-2 containing a quaternary ammonium moiety together with a hydroxymethyl and diarylmethanol moiety in an optically pure form, respectively (Figure 1) [37]. In order to see the beneficial effect of the diarylmethanol structure in this catalysts, they were applied to the

Synthesis of chiral 3-substituted 3-amino-2-oxindoles through enantioselective catalytic nucleophilic additions to isatin imines

• Hélène Pellissier

Beilstein J. Org. Chem. 2018, 14, 1349–1369, doi:10.3762/bjoc.14.114

• organocatalyzed methodologies [10][13]. The simplest method to prepare chiral quaternary 3-amino-2-oxindoles is based on enantioselective catalytic nucleophilic additions to isatin imines. This is not only because of the easy access to isatin imines, but also by the possibility of using a wide range of

A survey of chiral hypervalent iodine reagents in asymmetric synthesis

• Soumen Ghosh,
• Suman Pradhan and
• Indranil Chatterjee

Beilstein J. Org. Chem. 2018, 14, 1244–1262, doi:10.3762/bjoc.14.107

• -symmetric I(III) reagent 8b was used to obtain high enantioselectivity. Ishihara et al. appealingly reported an oxidative cycloetherification of ketophenols 92 in the presence of an in situ generated chiral quaternary ammonium (hypo)iodite salt 94, with hydrogen peroxide as an oxidant to deliver chiral

• -oxytosylation of carbonyls. Asymmetric α-oxygenation and α-amination of carbonyls reported by Wirth et al. Asymmetric α-functionalization of ketophenols using chiral quaternary ammonium (hypo)iodite salt reported by Ishihara et al. Oxidative Intramolecular coupling by Gong et al. α-Sulfonyl and α-phosphoryl

Hypervalent iodine(III)-mediated decarboxylative acetoxylation at tertiary and benzylic carbon centers

• Kensuke Kiyokawa,
• Daichi Okumatsu and
• Satoshi Minakata

Beilstein J. Org. Chem. 2018, 14, 1046–1050, doi:10.3762/bjoc.14.92

• I2 in a CH2Cl2/AcOH mixed solvent is reported. The reaction was successfully applied to two types of carboxylic acids containing an α-quaternary and a benzylic carbon center under mild reaction conditions. The resulting acetates were readily converted into the corresponding alcohols by hydrolysis

• applications have not been explored. We recently reported on the decarboxylative Ritter-type amination of carboxylic acids containing an α-quaternary carbon center using a combination of PhI(OAc)2 and I2 to produce the corresponding α-tertiary amine derivatives (Scheme 1) [25]. Mechanistic investigations

• reaction, namely acetoxylation, via the oxidative displacement of an iodine atom of the in situ generated alkyl iodide by PhI(OAc)2 [26]. Herein, we report on the decarboxylative acetoxylation of carboxylic acids that contain an α-quaternary carbon center using PhI(OAc)2 and I2 in a CH2Cl2/AcOH mixed

Methyl isocyanide as a convertible functional group for the synthesis of spirocyclic oxindole γ-lactams via post-Ugi-4CR/transamidation/cyclization in a one-pot, three-step sequence

• Amarendar Reddy Maddirala and
• Peter R. Andreana

Beilstein J. Org. Chem. 2018, 14, 875–883, doi:10.3762/bjoc.14.74

• spiro[indoline-3,2'-pyrrolidine]-2,5'-diones, via a post-Ugi-domino transamidation/cyclization sequential process, has been achieved in three sequential steps utilizing a one-pot reaction protocol. The variation in carboxylic acid substrates allows for the generation of new chiral racemic quaternary

Bromide-assisted chemoselective Heck reaction of 3-bromoindazoles under high-speed ball-milling conditions: synthesis of axitinib

• Jingbo Yu,
• Zikun Hong,
• Xinjie Yang,
• Yu Jiang,
• Zhijiang Jiang and
• Weike Su

Beilstein J. Org. Chem. 2018, 14, 786–795, doi:10.3762/bjoc.14.66

• ]. Despite two proposals for the role of quaternary ammonium salts NR4+X−, (1) Pd(0) stablizer and (2) phase transfer were suggested [28][29][30], their effects and functions remain unrevealed. Hence, we want to get insight to the reaction pathway and the actual functions of NR4+X− for better inhibiting the

• , suggesting the bromide ion plays an important role in ameliorating the reaction selectivity (Table S1, entries 9–11). Further investigating the alkyl chain (R) of NR4+Br− showed that the medium-length butyl was most efficient (Table S1, entries 5–7). In order to see whether the quaternary ammonium salt had

Enantioselective dioxytosylation of styrenes using lactate-based chiral hypervalent iodine(III)

• Morifumi Fujita,
• Koki Miura and
• Takashi Sugimura

Beilstein J. Org. Chem. 2018, 14, 659–663, doi:10.3762/bjoc.14.53

• substituted styrenes. The phenonium cation intermediate I4 contains two reaction sites on the ethylene bridge. Electron donation due to the lone pair on the oxygen atom of the internal tosyloxy group may weaken the bond between the tosyloxy-bonded carbon and the quaternary carbon in I4. The reaction of

Mannich base-connected syntheses mediated by ortho-quinone methides

• Petra Barta,
• Ferenc Fülöp and
• István Szatmári

Beilstein J. Org. Chem. 2018, 14, 560–575, doi:10.3762/bjoc.14.43

• intermediate reacts with the nucleophile (dienophile) species in different reactions to form a wide range of heterocyclic compounds. Reactions with C=C dienophiles Reactions of o-QMs with different C=C dienophiles are listed in Table 3. Osyanin et al. reported the efficient reaction of quaternary ammonium salt

• Mannich bases with malononitrile catalysed by 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) [67]. It is known that the use of quaternary ammonium salts offers the easier removal of the amino residue and, therefore, trapping the transient electrophilic species at lower temperature. Carrying out the reactions in

Latest development in the synthesis of ursodeoxycholic acid (UDCA): a critical review

• Fabio Tonin and
• Isabel W. C. E. Arends

Beilstein J. Org. Chem. 2018, 14, 470–483, doi:10.3762/bjoc.14.33

• ), showing a molecular weight around 30 kDa and a homodimeric or homotetrameric quaternary structure. Reported 7α-HSDHs were isolated from both aerobic and anaerobic bacteria: the state of art, together with the cofactor dependence and the specific activities, are summarized in Table 2 [33][63][64][65][66