Novel (2-amino-4-arylimidazolyl)propanoic acids and pyrrolo[1,2-c]imidazoles via the domino reactions of 2-amino-4-arylimidazoles with carbonyl and methylene active compounds

• Victoria V. Lipson,
• Tetiana L. Pavlovska,
• Nataliya V. Svetlichnaya,
• Anna A. Poryvai,
• Nikolay Yu. Gorobets,
• Erik V. Van der Eycken,
• Irina S. Konovalova,
• Svetlana V. Shiskina,
• Alexander V. Borisov,
• Vladimir I. Musatov and
• Alexander V. Mazepa

Beilstein J. Org. Chem. 2019, 15, 1032–1045, doi:10.3762/bjoc.15.101

• signals of the ABX protons of the propionyl fragment – СНХ at 4.60–4.30 ppm and СН2АВ at 3.00–2.60 ppm. Finally, the structure of acids 11 was confirmed by X-ray diffraction data of the sample compound 11b (Figure 4). Compound 11b was found to be a zwitterion and exists as monohydrate in the crystal phase

• 1.332(2) Å, the C1–N3 bond length is 1.337(3) Å and the N1–C1 bond length is 1.340(2) Å) allows to describe the zwitterion as superposition of three forms with different location of the positive charge (Scheme 3). Literatur data concerning pyrrolo[1,2-c]imidazol-5-ones is quite limited and the known 6,7

Selective formation of a zwitterion adduct and bicarbonate salt in the efficient CO₂ fixation by N-benzyl cyclic guanidine under dry and wet conditions

• Yoshiaki Yoshida,
• Naoto Aoyagi and
• Takeshi Endo

Beilstein J. Org. Chem. 2018, 14, 2204–2211, doi:10.3762/bjoc.14.194

• . In addition, the zwitterion adduct 2 and bicarbonate salt 3 were selectively prepared from 1 under dry (in anhydrous CH3CN) and wet (in CH3CN containing an equimolar amount of water for 1) conditions, respectively. Both compounds 2 and 3 were isolated as white solids and their structures were

• characterized in detail by elemental analysis, FTIR-ATR, solid-state NMR, TGA, and DFT calculation. These analytical results obviously revealed the formation of a zwitterion adduct and bicarbonate salt from N-benzyl cyclic guanidine and CO2. Especially, the zwitterion adduct of the monocyclic guanidine

• derivative and CO2 was isolated and characterized for the first time. Keywords: bicarbonate salt; carbon dioxide adsorption; cyclic guanidine; repeatable capture and release; zwitterion adduct; Introduction Recently, various reactions with CO2 as a cheap and green carbon reagent have been developed not

Phosphodiester models for cleavage of nucleic acids

• Satu Mikkola,
• Tuomas Lönnberg and
• Harri Lönnberg

Beilstein J. Org. Chem. 2018, 14, 803–837, doi:10.3762/bjoc.14.68

• , one order of magnitude faster than the cleavage of the zwitterion. This observation has led to the conclusion that the monoanion reacts through a minor tautomer having the 2´-OH deprotonated and the amino group protonated. The protonated amino group may facilitate the attack of the 2´-oxyanion by H

Rh(II)-mediated domino [4 + 1]-annulation of α-cyanothioacetamides using diazoesters: A new entry for the synthesis of multisubstituted thiophenes

• Jury J. Medvedev,
• Ilya V. Efimov,
• Yuri M. Shafran,
• Vitaliy V. Suslonov,
• Vasiliy A. Bakulev and
• Valerij A. Nikolaev

Beilstein J. Org. Chem. 2017, 13, 2569–2576, doi:10.3762/bjoc.13.253

• or 5. Principally, thiophenes 3 and 5 could be derived from the S-ylide B in a somewhat different way, as for instance: coordination E of cyano group in S-ylide with a rhodium catalyst [63] gives rise to zwitterion F with a negative charge located on the rhodium atom, followed by recovery of the

Dialkyl dicyanofumarates and dicyanomaleates as versatile building blocks for synthetic organic chemistry and mechanistic studies

• Grzegorz Mlostoń and
• Heinz Heimgartner

Beilstein J. Org. Chem. 2017, 13, 2235–2251, doi:10.3762/bjoc.13.221

• converts into the orthoester 10 via insertion into the C–O bond. The reaction mechanism for the formation of 8 and 9 comprises the initial attack of the nucleophilic carbene onto the electron-deficient C atom of E-1b to give an intermediate zwitterion 11. The latter undergoes two competitive reactions. The

• first one is the ring closure leading to 9, and the second one involves the addition of a second carbene followed by ring closure to yield 8. The reaction with Z-1b led to the same set of products with trans-orientation of the substituents in 8 indicating the appearance of an intermediate zwitterion 11

• mechanistic explanation of this cyclopropanation reaction is based on the assumption that the intermediate zwitterion 18a undergoes either a 1,3- or 1,5-electrocyclization leading to 15 or thiolanes 19a. The experiments with both isomers of 1b showed that the reactions proceeded non-stereospecifically and

Dimerization reactions of aryl selenophen-2-yl-substituted thiocarbonyl S-methanides as diradical processes: a computational study

• Michael L. McKee,
• Grzegorz Mlostoń,
• Katarzyna Urbaniak and
• Heinz Heimgartner

Beilstein J. Org. Chem. 2017, 13, 410–416, doi:10.3762/bjoc.13.44

• with solvation effects (assuming ∆H(solv) = ∆G(solv)) to obtain enthalpies at 298 K in THF (Equation 1). The calculated entropy was used to determine the –T∆S term to form free energies at 298 K in THF (Equation 2). Structures of the reactive intermediates as a diradical 6 or a zwitterion 7 in the

Decarboxylative and dehydrative coupling of dienoic acids and pentadienyl alcohols to form 1,3,6,8-tetraenes

• Ghina’a I. Abu Deiab,
• Mohammed H. Al-Huniti,
• I. F. Dempsey Hyatt,
• Emma E. Nagy,
• Kristen E. Gettys,
• Sommayah S. Sayed,
• Christine M. Joliat,
• Paige E. Daniel,
• Rupa M. Vummalaneni,
• Andrew T. Morehead Jr,
• Andrew L. Sargent and
• Mitchell P. Croatt

Beilstein J. Org. Chem. 2017, 13, 384–392, doi:10.3762/bjoc.13.41

• . Pathway B involves a Morita–Baylis–Hillman type process. The role of water would be to hydrogen bond to the carboxylate to make the system more electrophilic (B). This would accelerate the addition of the phosphine to generate zwitterion C [58]. Preliminary modeling for this ion indicates that both the

Catalytic Wittig and aza-Wittig reactions

• Zhiqi Lao and
• Patrick H. Toy

Beilstein J. Org. Chem. 2016, 12, 2577–2587, doi:10.3762/bjoc.12.253

• products 32 catalyzed by tributylphosphine (33, 0.05 equivalents) (Scheme 9) [26]. In these transformations the initial reaction between 31 and 33 generated zwitterion 34, that underwent internal proton transfer to generate ylide 35. This in turn reacted with aldehyde 6 to form 32 and phenylsilane was used

Strecker degradation of amino acids promoted by a camphor-derived sulfonamide

• M. Fernanda N. N. Carvalho,
• M. João Ferreira,
• Ana S. O. Knittel,
• Maria da Conceição Oliveira,
• João Costa Pessoa,
• Rudolf Herrmann and
• Gabriele Wagner

Beilstein J. Org. Chem. 2016, 12, 732–744, doi:10.3762/bjoc.12.73

• may expect such a barrier in the tautomerization (probably catalyzed by water) which forms the zwitterion by proton migration from the neutral imine. The experimental results on Strecker degradation have been summarized in a rule that says that the most efficient promoters have a structure of the type

• is interrupted as in the zwitterion 4. The latter would represent the intermediate if a hydride shift occurred in the imine before the decarboxylation step (Figure 7, upper row). In contrast, the zwitterions 5 and 6 readily lose CO2 upon geometry optimization, since the negative charge is efficiently

• compounds as well as carboxylate anions. This is different in the ninhydrin reaction where the corresponding anions lose CO2 upon attempted geometry optimization. Decarboxylation of the imines of the oxoimine 1 only occurs when a zwitterion is formed by proton transfer to one of the two nitrogen atoms. This

Asymmetric α-amination of 3-substituted oxindoles using chiral bifunctional phosphine catalysts

• Qiao-Wen Jin,
• Zhuo Chai,
• You-Ming Huang,
• Gang Zou and
• Gang Zhao

Beilstein J. Org. Chem. 2016, 12, 725–731, doi:10.3762/bjoc.12.72

• novel amino acid-derived chiral bifunctional organophosphine catalysts, which have successfully applied to catalyze various asymmetric reactions [40][41]. As a general concept, a tertiary phosphine adds to an electrophilic reactant to form a zwitterion which serves as either a nucleophile or a Bronsted

• base to participate in the catalytic cycle. In 2015, we reported a novel asymmetric dual-reagent catalysis strategy based on these chiral phosphine catalysts [42], in which the zwitterion in situ generated from the chiral phosphine and methyl acrylate acted as an efficient catalyst for the asymmetric

• absolute configurations of other adducts 3b–t were assigned by analogy. To get some insight into this reaction, 31P NMR of the mixture of 4d (0.5 mol %) and 2a (0.12 mmol) in CD2Cl2 was monitored, followed by the addition of 1a (0.1 mmol) in to the mixture (Figure 1). The formation of zwitterion

Recent advances in N-heterocyclic carbene (NHC)-catalysed benzoin reactions

• Rajeev S. Menon,
• Akkattu T. Biju and
• Vijay Nair

Beilstein J. Org. Chem. 2016, 12, 444–461, doi:10.3762/bjoc.12.47

• . Breslow postulated in 1958 a mechanistic rationale for the thiazolium salt-catalysed benzoin reaction [3]. He depicted the catalytically active species as a thiazolium zwitterion (the resonance structure of an NHC) and proposed that the reaction proceeds via an enaminol intermediate. The latter is now

Fe(II)/Et₃N-Relay-catalyzed domino reaction of isoxazoles with imidazolium salts in the synthesis of methyl 4-imidazolylpyrrole-2-carboxylates, its ylide and betaine derivatives

• Ekaterina E. Galenko,
• Olesya A. Tomashenko,
• Alexander F. Khlebnikov,
• Mikhail S. Novikov and
• Taras L. Panikorovskii

Beilstein J. Org. Chem. 2015, 11, 1732–1740, doi:10.3762/bjoc.11.189

• carbenes 3 are more thermodynamically stable than the corresponding ylides 2. However, as one can expect, the solvent stabilizes the zwitterion species much better than the uncharged ones. According to the DFT calculations in solution the equilibrium is shifted to the ylide side and the higher the polarity

Chiral phosphines in nucleophilic organocatalysis

• Yumei Xiao,
• Zhanhu Sun,
• Hongchao Guo and
• Ohyun Kwon

Beilstein J. Org. Chem. 2014, 10, 2089–2121, doi:10.3762/bjoc.10.218

• phosphine, the β-phosphonium dienolate zwitterion becomes protonated at its α-carbon atom, resulting in the formation of vinylphosphonium species and anionic nucleophiles. The nucleophile anion then undergoes γ-umpolung addition to the γ-carbon atom of the vinylphosphonium species, producing a phosphonium

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

• ground state biradicaloid or zwitterion is the product determining step. In both cases, the aromaticity of both rings is lost upon formation of the Favorskii cyclopropanone intermediates 38 and 41. However, this rationale also falls short because the reactions of the similar biradicaloid or zwitterion

• are known to undergo nucleophilic substitution and not reduction to the methyl ketone products 6, 12 or 15 [38][39]. Substitution by solvent would trap the intermediate biradicaloid (or zwitterion) to form, in the case of 2,6-HNA, the α-methoxy ketone 42, which was not detected among the photoproducts

Proton transfers in the Strecker reaction revealed by DFT calculations

• Shinichi Yamabe,
• Guixiang Zeng,
• Wei Guan and
• Shigeyoshi Sakaki

Beilstein J. Org. Chem. 2014, 10, 1765–1774, doi:10.3762/bjoc.10.184

• OH2 addition to afford a zwitterion compound MeC(NH2)H-C(OH)(O−)-NH3+ 15. The ΔE≠ and ΔE values of the H2O addition step relative to the energy of 13 are 30.5 and 25.8 kcal/mol, respectively. After that, the NH3 moiety is ready to dissociate from 15 to produce the product (R)-alanine 16 with a ΔE

A promising cellulose-based polyzwitterion with pH-sensitive charges

• Thomas Elschner and
• Thomas Heinze

Beilstein J. Org. Chem. 2014, 10, 1549–1556, doi:10.3762/bjoc.10.159

• of novel polyzwitterions based on cellulose carbamate with carboxylic- and primary amino groups is discussed. Starting from cellulose carbonate, the fully protected zwitterion is efficiently synthesized that could be converted into the polyanion, polycation, and polyzwitterion via the orthogonal

Preparation of phosphines through C–P bond formation

• Iris Wauters,
• Wouter Debrouwer and
• Christian V. Stevens

Beilstein J. Org. Chem. 2014, 10, 1064–1096, doi:10.3762/bjoc.10.106

• giving a platinum–phosphido complex. Subsequent nucleophilic attack on a Michael acceptor alkene was suggested to lead to a zwitterion intermediate. Addition of a protic additive was beneficial for the selectivity and reaction rate [95]. Several chiral cyclic phosphines were acquired via the lanthanide

Regioselective S_N2' Mitsunobu reaction of Morita–Baylis–Hillman alcohols: A facile and stereoselective synthesis of α-alkylidene-β-hydrazino acid derivatives

• Silong Xu,
• Jian Shang,
• Junjie Zhang and
• Yuhai Tang

Beilstein J. Org. Chem. 2014, 10, 990–995, doi:10.3762/bjoc.10.98

• azodicarboxylates 2 generates the Huisgen zwitterion intermediate 8 [37][38]. Subsequent proton transfer and phosphonium migration between 8 and the MBH alcohol 1 produce an oxophosphonium intermediate 9 and a hydrazine anionic species 10 [36]. Finally, an expedient SN2' attack of species 10 on 9, probably

One-pot three-component synthesis and photophysical characteristics of novel triene merocyanines

• Christian Muschelknautz,
• Robin Visse,
• Jan Nordmann and
• Thomas J. J. Müller

Beilstein J. Org. Chem. 2014, 10, 599–612, doi:10.3762/bjoc.10.51

• minute electronic distributions in the zwitterionic key intermediate, which is controlled in the allenyl enolate moiety by the indolyl nitrogen substituent R1 and by the fragment X on the iminium part, which participates in the stabilization on that side of the zwitterion. The former hypothesis is

• the outcome of the sequence. The latter hypothesis of the iminium-ion stabilization obviously influences the lifetime of the zwitterion 13. Furthermore the enamine formed by deprotonation of 9 is a S,N-ketene acetal, which is significantly more nucleophilic than Fischer’s base (7). The higher

• reactivity of the latter enamine and the higher thermodynamic stability of the iminium intermediate both account for a stepwise pathway that proceeds via the intermediacy of zwitterion 13. Therefore, if intermediate 13 is long lived enough to undergo the prototropy the merocyanines 10 will be the obvious

Recent applications of the divinylcyclopropane–cycloheptadiene rearrangement in organic synthesis

• Sebastian Krüger and
• Tanja Gaich

Beilstein J. Org. Chem. 2014, 10, 163–193, doi:10.3762/bjoc.10.14

• formation between vinyl-diazo compound 317 and imine 318 has been found by Doyle [224][225][226]. Rearrangement occurred smoothly to give desired dihydroazepine 320. Note that the authors suggest a transition state including an opened aziridine zwitterion. Alternatively, a cyclopropylamine can be used in an

Organobase-catalyzed three-component reactions for the synthesis of 4H-2-aminopyrans, condensed pyrans and polysubstituted benzenes

• Moustafa Sherief Moustafa,
• Saleh Mohammed Al-Mousawi,
• Maghraby Ali Selim,
• Ahmed Mohamed Mosallam and
• Mohamed Hilmy Elnagdi

Beilstein J. Org. Chem. 2014, 10, 141–149, doi:10.3762/bjoc.10.11

• produce zwitterion 35a. Reaction of 35a or its protonated form with malononitrile, which is likely generated by hydrolysis of 7a, then forms 36a that cyclizes and aromatizes by loss of HCN to yield 37a. This sequence is closely related to the one described above for the formation of benzoic acid

Less reactive dipoles of diazodicarbonyl compounds in reaction with cycloaliphatic thioketones – First evidence for the 1,3-oxathiole–thiocarbonyl ylide interconversion

• Valerij A. Nikolaev,
• Alexey V. Ivanov,
• Ludmila L. Rodina and
• Grzegorz Mlostoń

Beilstein J. Org. Chem. 2013, 9, 2751–2761, doi:10.3762/bjoc.9.309

• spontaneous desulfurization and convert into tetrasubstituted alkenes [20]. 2) Pathway B assumes a stepwise cycloaddition of the diazo-1,3-dipole with the C=S bond leading to the initial formation of the diazonium zwitterion 11. This step is followed either by the ring closure to give thiadiazoline 10 or by

• intermediate 1,3,4-thiadiazoline or a diazonium zwitterion. Next, electrocyclization of the transient thiocarbonyl ylide leads to spirocyclic 1,3-oxathioles in yields of up to 88%. In similar reactions of diazomalonate 2e, a competitive process of 1,3-dipolar electrocyclization is observed. It led to the

Diastereoselectivity in the Staudinger reaction of pentafluorosulfanylaldimines and ketimines

• Alexander Penger,
• Cortney N. von Hahmann,
• Alexander S. Filatov and
• John T. Welch

Beilstein J. Org. Chem. 2013, 9, 2675–2680, doi:10.3762/bjoc.9.303

• group as shown in A. Cornforth control of the ring closure step of the zwitterion (B in Scheme 4) where the SF5 would be antiperiplanar to the iminium ion would lead to the observed diastereoselectivity (Scheme 1). This finding is consistent with dipolar effects being most important in reactions with

Sequential Diels–Alder/[3,3]-sigmatropic rearrangement reactions of β-nitrostyrene with 3-methyl-1,3-pentadiene

• Peter A. Wade,
• Alma Pipic,
• Matthias Zeller and
• Panagiota Tsetsakos

Beilstein J. Org. Chem. 2013, 9, 2137–2146, doi:10.3762/bjoc.9.251

• intermediate. The initially isolated nitronic ester cycloadducts underwent tin(IV)-catalyzed interconversion, presumably via zwitterion intermediates. Cycloadducts derived from the reaction at the less substituted double bond of (E)-3-methyl-1,3-pentadiene underwent a [3,3]-sigmatropic rearrangement on heating

• conditions leading to loss of stereointegrity. However, a more likely explanation is that cycloaddition occurs by a stepwise process involving a tin(IV)-coordinated zwitterion intermediate. The reaction with pure Z-diene 1b gave significantly different results. Only four cycloadducts were obtained, all of

• nitroalkene Diels–Alder reactions have been proposed. Denmark et al. favor a stepwise process proceeding via a zwitterion intermediate [11][14]. Alkene stereointegrity is normally retained, presumably owing to a cyclic conformation dictated by charge interaction between the cation center and tin nitronate

Presence or absence of a novel charge-transfer complex in the base-catalyzed hydrolysis of N-ethylbenzamide or ethyl benzoate

• Shinichi Yamabe,
• Wei Guan and
• Shigeyoshi Sakaki

Beilstein J. Org. Chem. 2013, 9, 185–196, doi:10.3762/bjoc.9.22

• of the carbonyl 18O exchange and D2O solvent kinetic isotope effects [21][22][23][24][25]. They suggested intervention of a pair of a zwitterion and OH− as well as that of the anionic tetrahedral intermediate (Scheme 1). Although many theoretical studies of the basic amide hydrolysis have been

• reported so far [26][27][28][29][30][31][32][33][34][35][36][37], the presence or absence of the zwitterion has not been scrutinized. As for zwitterions of amino acids and peptides, the effect of the solvent on the structure and various spectra has been examined carefully [38][39][40][41][42][43][44][45

• ][46]. Explicit solvent models were reported to be necessary, and it was shown that the use of continuum solvent models is not adequate. For instance, Degtyarenko and co-workers demonstrated that 20 water molecules are needed to completely solvate the L-alanine zwitterion [46]. The average number of