Ortho-ester-substituted diaryliodonium salts enabled regioselective arylocyclization of naphthols toward 3,4-benzocoumarins

• Ke Jiang,
• Cheng Pan,
• Limin Wang,
• Hao-Yang Wang and
• Jianwei Han

Beilstein J. Org. Chem. 2024, 20, 841–851, doi:10.3762/bjoc.20.76

• -trifluoroborate-substituted diaryliodonium salts furnished iodonium zwitterions as bifunctional reagents [22][23][24][25]. Additionally, ortho-trifluoromethanesulfonate, N-sulfonyl, or tosylmethylene-substituted diaryliodonium salts can undergo intramolecular aryl migrations [26][27][28]. More recently, we

Using the phospha-Michael reaction for making phosphonium phenolate zwitterions

• Matthias R. Steiner,
• Max Schmallegger,
• Larissa Donner,
• Johann A. Hlina,
• Christoph Marschner,
• Judith Baumgartner and
• Christian Slugovc

Beilstein J. Org. Chem. 2024, 20, 41–51, doi:10.3762/bjoc.20.6

• phenolate zwitterions at room temperature. Nine different zwitterions were synthesized and fully characterized. Zwitterions with the poor Michael acceptors methyl methacrylate and methyl crotonate formed, but could not be isolated in pure form. The solid-state structures of two phosphonium phenolate

• regarded as stable phosphonium enolate zwitterions. The first zwitterions of this type were published in 1955 [31], but the first crystal structure of a phosphonium enolate zwitterion was reported only in 2007 by Zhu et al., who synthesized the compound via a three-component coupling between an

• alkylphosphine, an aldehyde and an alkyne [32]. Another example resulting from phosphine addition to α,β-unsaturated aldehydes was published shortly afterwards [33]. Phosphonium carboxylate zwitterions have been obtained by the reaction of phosphines with acrylic acid [8] and ortho-carboxylated arylphosphines

Aldiminium and 1,2,3-triazolium dithiocarboxylate zwitterions derived from cyclic (alkyl)(amino) and mesoionic carbenes

• Nedra Touj,
• François Mazars,
• Guillermo Zaragoza and
• Lionel Delaude

Beilstein J. Org. Chem. 2023, 19, 1947–1956, doi:10.3762/bjoc.19.145

• , MIC·CS2, and NHC·CS2 zwitterions displayed similar electronic properties and featured the same bite angle. Yet, their steric properties are liable to ample modifications by varying the exact nature of their cationic heterocycle and its substituents. Keywords: betaines; carbenes; ligand effects; nitrogen

• heterocycles; zwitterions; Introduction Following the seminal discovery from the group of Arduengo, who isolated and fully characterized 1,3-di(1-adamantyl)imidazol-2-ylidene in 1991 [1], stable divalent carbon species have evolved from fleeting intermediates to ubiquitous catalysts, ligands, and reagents in

• -dithiocarboxylate zwitterions (Figure 2) [30][31][32][33][34][35][36][37][38][39][40][41][42][43]. These 1,1-dithiolate inner salts strongly bind main group elements and transition metals through various coordination modes. Indeed, we and others have already reported the synthesis of diverse metallic complexes

Decarboxylative 1,3-dipolar cycloaddition of amino acids for the synthesis of heterocyclic compounds

• Xiaofeng Zhang,
• Xiaoming Ma and
• Wei Zhang

Beilstein J. Org. Chem. 2023, 19, 1677–1693, doi:10.3762/bjoc.19.123

• : A1-type AMYs can be generated from the condensation of aldehydes with α- and N-dialkylglycine esters, A2-type AMYs are derived from α-alkylglycine esters, A3-type AMYs are derived from N-alkylglycine esters, and A4-type AMYs are derived from glycine esters. Stabilized zwitterions A1–A4 have the

Electron-rich triarylphosphines as nucleophilic catalysts for oxa-Michael reactions

• Susanne M. Fischer,
• Simon Renner,
• A. Daniel Boese and
• Christian Slugovc

Beilstein J. Org. Chem. 2021, 17, 1689–1697, doi:10.3762/bjoc.17.117

• (MMTPP), −87.9 kJ/mol (TMTPP), and −74.5 kJ/mol (PMe3) in favor of the educts acrylonitrile and phosphine. Accordingly, the zwitterion formed from PMe3 is in relation the most stable and the zwitterion formed from TPP the most unstable one within the series. The stability trend of the zwitterions based

• ). Right: Relative stabilities of the zwitterions formed upon reaction of Michael acceptors 1–3 with the phosphines (the cartoon shows the structures of the educts acrylonitrile and TMTPP (left, behind the chart) and the corresponding zwitterion (right, above), optimized at the B3LYP/def2-TZVPPD level of

1,5-Phosphonium betaines from N-triflylpropiolamides, triphenylphosphane, and active methylene compounds

• Vito A. Fiore,
• Chiara Freisler and
• Gerhard Maas

Beilstein J. Org. Chem. 2019, 15, 2603–2611, doi:10.3762/bjoc.15.253

• -Michael reaction; propiolamides; Introduction Beside the well-known phosphonium ylides (Wittig ylides, methylenephosphoranes), various other types of zwitterions containing a tetravalent phosphonium moiety (phosphonium betaines) exist. They are often considered as reaction intermediates, but reports on

• propadienones. The presentation of 1,5-zwitterions 3 with the negative charge residing on a carbon atom is more or less a formal one. The structural and spectroscopic data (vide infra) support the view that the mesomeric enolate structure 3’ (see Scheme 3) significantly contributes to the bonding state and that

• an even wider delocalization of the negative charge, represented by formula 3”, does occur. Therefore, these zwitterions are better described as 1-phosphonium-5-oxabetaines than -5-carbabetaines. Furthermore, they represent a novel type of phosphonium enolate betaines and may be considered as

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

• leading to zwitterronic intermediates 8 and 8’. This would result in an increase of conformational flexibility thereby facilitating the nucleophilic displacement of the ammonium by the phosphinite through transition states TS1 and TS2 (SN2-type process), respectively. Oxaphospholanium zwitterions 9 and 9

Adhesion, forces and the stability of interfaces

• Robin Guttmann,
• Johannes Hoja,
• Christoph Lechner,
• Reinhard J. Maurer and
• Alexander F. Sax

Beilstein J. Org. Chem. 2019, 15, 106–129, doi:10.3762/bjoc.15.12

• ., when a large n-alkane changes from the linear to the hairpin structure; non-covalent interaction, on the other hand, does not exclude creation and stabilization of cation–anion pairs or zwitterions and their stabilization by Coulomb interaction. Weak molecular interaction is certainly the best term for

Oligonucleotide analogues with cationic backbone linkages

• Melissa Meng and
• Christian Ducho

Beilstein J. Org. Chem. 2018, 14, 1293–1308, doi:10.3762/bjoc.14.111

• motifs, and nucleosyl amino acid (NAA)-derived modifications. The synthesis and properties of the corresponding oligonucleotide analogues are described. Keywords: backbone modifications; cations; DNA; oligonucleotides; zwitterions; Introduction Oligonucleotides have the unique ability to bind

Conformational study of L-methionine and L-cysteine derivatives through quantum chemical calculations and ³J_HH coupling constant analyses

• Weslley G. D. P. Silva,
• Carolyne B. Braga and
• Roberto Rittner

Beilstein J. Org. Chem. 2017, 13, 925–937, doi:10.3762/bjoc.13.94

• challenging for chemists and physicists due to the particular amino acid properties, such as high melting points, low vapor pressures and the occurrence of zwitterions in solution. Nevertheless, taking into account the recent experimental and theoretical developments, studies dealing with amino acids have

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

• case of similar thiocarbonyl S-isopropanides, the intermediate zwitterions, formed in the course of the attempted [3 + 2]-cycloaddition with electron-deficient ethenes, undergo 1,3-electrocyclization yielding mixtures of stereoisomeric cyclopropanes in addition to the expected 5-membered thiolanes

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

• connected by a –N= bridge, and thus has a structural analogy to the colored product Ruhemann´s purple obtained by the ninhydrin reaction with amino acids. A plausible reaction mechanism that involves zwitterions, a Strecker degradation of an intermediate imine and water-catalyzed tautomerizations was

• structure of such zwitterions, decarboxylation occurs instead. Thus, we do not find a transition state, and the activation barrier approaches zero. Experimentally, Strecker degradations are not instantaneous, which means that there must exist at least a small barrier somewhere in the reaction sequence. One

• 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

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

• -substituted oxindole catalyzed by chiral amino acid-derived organophosphine catalysts, in which the zwitterions in situ generated from the phosphine and azodicarboxylates serve as highly efficient catalysts [44] (Scheme 1). Results and Discussion Initially, the reaction between 3-phenyloxindole 1a and DEAD

Efficient synthetic protocols for the preparation of common N-heterocyclic carbene precursors

• Morgan Hans,
• Jan Lorkowski,
• Albert Demonceau and
• Lionel Delaude

Beilstein J. Org. Chem. 2015, 11, 2318–2325, doi:10.3762/bjoc.11.252

• serves de facto as a carbene source for most catalytic and synthetic purposes. Alternative methods to generate NHCs without the intervention of a base, which might lead to unwanted side-reactions, include the facile cleavage of NHC·CO2 zwitterions (Scheme 1, path B) [31][32][33][34][35], the thermolysis

• tetrafluoroborate without any apparent complication [59]. We have further optimized this procedure on the occasion of a mechanistic study of the Staudinger reaction catalyzed by NHC·ketene zwitterions (Scheme 5) [60]. Synthesis of 1,3-dimesitylimidazolinium chloride The “saturated” analogue of the IMes carbene, 1,3

Convenient preparation of high molecular weight poly(dimethylsiloxane) using thermally latent NHC-catalysis: a structure-activity correlation

• Stefan Naumann,
• Johannes Klein,
• Dongren Wang and
• Michael R. Buchmeiser

Beilstein J. Org. Chem. 2015, 11, 2261–2266, doi:10.3762/bjoc.11.246

• 7-iPr-CO2 and 6-Cy-CO2 could be connected to a low initiation efficiency and consequently low ratio of propagating zwitterions to monomer, resulting in high-molecular weight polymers. In contrast, a sterically uncongested, highly nucleophilic NHC as liberated from 5Me-Me-CO2 (Table 1, entry 12) is

Synthesis of tripodal catecholates and their immobilization on zinc oxide nanoparticles

• Franziska Klitsche,
• Julian Ramcke,
• Julia Migenda,
• Andreas Hensel,
• Tobias Vossmeyer,
• Horst Weller,
• Silvia Gross and
• Wolfgang Maison

Beilstein J. Org. Chem. 2015, 11, 678–686, doi:10.3762/bjoc.11.77

• derivatives bearing an additional effector moiety may be used to generate stable particles with tailored properties, good solubility and biocompatibility. Suitable effectors in this context are PEG [31][32][33], zwitterions [34][35] or polyglycerols [36][37] which, when immobilized on NPs, may be used to tune

NAA-modified DNA oligonucleotides with zwitterionic backbones: stereoselective synthesis of A–T phosphoramidite building blocks

• Boris Schmidtgall,
• Claudia Höbartner and
• Christian Ducho

Beilstein J. Org. Chem. 2015, 11, 50–60, doi:10.3762/bjoc.11.8

• to further establish the NAA-linkage as a useful addition to the existing 'toolbox' of backbone modifications for the design of bioactive oligonucleotide analogues. Keywords: backbone modifications; DNA; nucleic acids; oligonucleotides; stereoselective synthesis; zwitterions; Introduction

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

• summarized splendidly in several reviews, we do not cover these transformations, except for selected examples related to other reactions. Review 1 Chiral phosphine catalysts Nucleophilic phosphine catalysis often involves the formation of Lewis adducts, namely phosphonium (di)enolate zwitterions, as reaction

Pyrrolidine nucleotide analogs with a tunable conformation

• Lenka Poštová Slavětínská,
• Dominik Rejman and
• Radek Pohl

Beilstein J. Org. Chem. 2014, 10, 1967–1980, doi:10.3762/bjoc.10.205

• the compounds exist as zwitterions with a hydrogen bond between the negatively charged phosphonate moiety and the positively charged pyrrolidine nitrogen atom in the range of pD 3–9. The pD titration experiments have also revealed the deuteration/dedeuteration of adenine and thymine nucleobases. In

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

• . While polyzwitterions based on N-functionalized chitosan [14][15] or 6-desoxy-6-aminocelluloses [16] are composed like synthetic polybetaines, a few cellulose-based zwitterions are described where the isoelectric point and the properties in solution could be tuned by varying the substitution pattern [17

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

• product. Therefore, the local charge density in 13 is most crucial for the bifurcation and, hence, for the product formation. For scrutinizing this rationale we computed the electrostatic charges on the atoms 1–7 of the allenyl enolate moiety of model zwitterions 16, which only differ by the N-substituent

Synthesis of five- and six-membered cyclic organic peroxides: Key transformations into peroxide ring-retaining products

• Alexander O. Terent'ev,
• Dmitry A. Borisov,
• Vera A. Vil’ and
• Valery M. Dembitsky

Beilstein J. Org. Chem. 2014, 10, 34–114, doi:10.3762/bjoc.10.6

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

• where ternary adduct 12a,b is formed. Consistent with the presence of these zwitterions, the related open-chain adduct 13 was a minor product obtained from the reaction of Z-diene 1b and β-nitrostyrene in dichloromethane solution. Nitronic ester structure determination Structure assignments for nitronic

• nitronic esters 2 and 3 was also examined. Starting with either nitronic ester 2 or nitronic ester 3 resulted in a final 60:40 ratio of 2,3, respectively, after only 20 minutes. Bond scission to give zwitterions is thought to lead to isomerization in these reactions. These zwitterion intermediates are

• the analogous cyclo zwitterion 15, structurally identical with 11b. Interestingly, these cyclo zwitterions should be capable of closing in multiple ways, either to give nitronic esters or to give isomeric nitro compounds. Nitronic ester 5 was first converted to a mixture of 5 and 6 and eventually in

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

• 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

Polar reactions of acyclic conjugated bisallenes

• Reiner Stamm and
• Henning Hopf

Beilstein J. Org. Chem. 2013, 9, 36–48, doi:10.3762/bjoc.9.5

• , which is in equilibrium with its conformational isomer 32. Ring-opening of these strained intermediates then provides the “stretched” and the “closed” zwitterions 33 and 34, respectively. Whereas the open form 33 is intercepted by the anion derived from the epoxidation reagent, m-chlorobenzoic acid