Metal-mediated aminocatalysis provides mild conditions: Enantioselective Michael addition mediated by primary amino catalysts and alkali-metal ions

• Matthias Leven,
• Jörg M. Neudörfl and
• Bernd Goldfuss

Beilstein J. Org. Chem. 2013, 9, 155–165, doi:10.3762/bjoc.9.18

• -hydroxycoumarin (1) to prochiral α,β-unsaturated ketones. Instead of acid additives, which sometimes lead to decomposition of sensitive components [18], alkali-metal ions are employed as very mild Lewis acids (Scheme 1). The activation of Michael acceptors by iminium ions enables asymmetric additions of 4

• seems to be clear that the zwitterionic chelate shown in Figure 1 is too inert to form imines with carbonylic compounds. The choice of alkali metal does not affect the ee very markedly and the ee’s obtained in Table 1 are in the moderate range (up to 47%). In order to elucidate if Lewis acid free imines

• could also react as Michael acceptors, experiments employing triethylammonium salts of the catalysts 5 and 7 (pH 9) were performed, and no conversions could be detected in all cases. Because lithium was identified as the most appropriate alkali-metal ion for application in the catalysis (Table 1), the

Low-generation dendrimers with a calixarene core and based on a chiral C₂-symmetric pyrrolidine as iminosugar mimics

• Marco Marradi,
• Stefano Cicchi,
• Francesco Sansone,
• Alessandro Casnati and
• Andrea Goti

Beilstein J. Org. Chem. 2012, 8, 951–957, doi:10.3762/bjoc.8.107

• of a considerable number of iminosugar-like moieties in a reduced volume and in a well-defined geometry. The inclusion of alkali-metal ions (sodium and potassium) in the polar cavity defined by the acetamide moieties at the lower rim of the calixarene was demonstrated, which allows also the

• water. The presence of acetamide moieties at the lower rim of the dendrimers 2 and 3 prompted us to explore the possibility to use alkali metal salts as allosteric effectors in the modulation of the shape and rigidity of the iminosugar presentation by the calixarene scaffold. A common way, in fact, used

• to rigidify the “mobile cone” structure of tetraalkoxycalix[4]arenes is to introduce strong donating groups, such as amide or ester [32][33], on the phenolic oxygen atoms and an alkali-metal ion. The cation, strongly coordinated by eight oxygen atoms in the polar region created at the lower rim

Discovery of practical production processes for arylsulfur pentafluorides and their higher homologues, bis- and tris(sulfur pentafluorides): Beginning of a new era of “super-trifluoromethyl” arene chemistry and its industry

• Teruo Umemoto,
• Lloyd M. Garrick and
• Norimichi Saito

Beilstein J. Org. Chem. 2012, 8, 461–471, doi:10.3762/bjoc.8.53

• an alkali metal fluoride, and (step 2) treatment of the resulting arylsulfur chlorotetrafluoride with a fluoride source, such as ZnF2, HF, and Sb(III/V) fluorides. The intermediate arylsulfur chlorotetrafluorides were isolated by distillation or recrystallization and characterized. The aspects of

Fifty years of oxacalix[3]arenes: A review

• Kevin Cottet,
• Paula M. Marcos and
• Peter J. Cragg

Beilstein J. Org. Chem. 2012, 8, 201–226, doi:10.3762/bjoc.8.22

• , derivatives containing carbonyl groups (ester, acid, amide and ketone) and heteroatoms, such as nitrogen and phosphorous, have been obtained. In 1993, Shinkai et al. [29] reported the synthesis of the first ethyl ester derivative 12a. In the belief that the alkali-metal template effect would lead

• -butyl ether 10 derivatives toward alkali-metal cations were estimated by extraction experiments from alkaline aqueous picrate solutions to CH2Cl2 [24], with the latter showing some preference for K+ (59% E) over Na+ (6%) and Cs+ (35%). Replacement of the alkyl groups by residues with additional binding

• was investigated by Masci in 1995 [54] who found that Kassoc values in CDCl3 were modest, ranging from 38 M−1 for N,N,N-trimethylanilinium to 90 M−1 for N,N-dimethylpyrrolidinium, but significantly greater than those of the dihomocalix[4]arene and tetrahomooxacalix[4]arene analogues. 4.1.2 Alkali

On the control of secondary carbanion structure utilising ligand effects during directed metallation

• Andrew E. H. Wheatley,
• Jonathan Clayden,
• Ian H. Hillier,
• Alison Campbell Smith,
• Mark A. Vincent,
• Laurence J. Taylor and
• Joanna Haywood

Beilstein J. Org. Chem. 2012, 8, 50–60, doi:10.3762/bjoc.8.5

• authenticated tertiary carbanions, significant similarities are seen insofar as the connectivity of the alkali metal is concerned when changing tridentate Lewis bases. Thus, whereas 6-Lil·PMDTA fails to show a Li–(α-C) interaction in the solid state, in Lil·DGME the corresponding distance (2.406(6) Å) suggests

PEG-embedded KBr₃: A recyclable catalyst for multicomponent coupling reaction for the efficient synthesis of functionalized piperidines

• Sanny Verma,
• Suman L. Jain and
• Bir Sain

Beilstein J. Org. Chem. 2011, 7, 1334–1341, doi:10.3762/bjoc.7.157

• alkali metal cations, as shown in Scheme 1. The developed catalyst 3 was readily prepared by the mixing of equimolar amounts of PEG400 (1) and KBr to give [K+PEG]Br− 2, which on subsequent reaction with Br2 resulted in a dark orange-red colored viscous liquid (see Experimental). The liquid was dried

Combined directed ortho-zincation and palladium-catalyzed strategies: Synthesis of 4,n-dimethoxy-substituted benzo[b]furans

• Verónica Guilarte,
• M. Pilar Castroviejo,
• Estela Álvarez and
• Roberto Sanz

Beilstein J. Org. Chem. 2011, 7, 1255–1260, doi:10.3762/bjoc.7.146

• compounds and different directing groups have been used to facilitate the deprotonation reaction [1][2][3][4][5]. Various strong bases such as alkyl lithiums and their derivatives (for instance, TMEDA-activated complexes [6] and heavier alkali metal tert-butoxide-complexed alkyl lithium reagents, known as

• ), the introduction in the last years of new organometallic “ate” complexes [8][9], which combine an alkali metal with either magnesium, zinc, aluminium, or copper, has allowed more selective metallation reactions. The milder reaction conditions required make these deprotonation reactions tolerant to the

• , as well as of meta-functionalized haloaromatics. In particular, the alkali metal mediated zincation reactions have turned out to be very useful processes and the structures and reaction pathways of TMP-zincates (TMP = 2,2,6,6-tetramethylpiperidine) have been studied in detail [15][16][17][18][19]. On

Meta-metallation of N,N-dimethylaniline: Contrasting direct sodium-mediated zincation with indirect sodiation-dialkylzinc co-complexation

• David R. Armstrong,
• Liam Balloch,
• Eva Hevia,
• Alan R. Kennedy,
• Robert E. Mulvey,
• Charles T. O'Hara and
• Stuart D. Robertson

Beilstein J. Org. Chem. 2011, 7, 1234–1248, doi:10.3762/bjoc.7.144

• -) metallation was favoured by direct sodium-mediated zincation. Keywords: alkali metal; crystal structure; isomerisation; metallation; zincation; Introduction While the metallation reaction remains an essential tool for constructing substituted aromatic compounds [1][2], the quest for new improved reagents

• typically at ambient temperature [11] and on the multi-gram scale with metallation rates comparable to those obtained for small scale processes [12]. Alkali metal zincates have also been given consideration, principally two-component dialkyl-amido zincates MZn(NR2)R′2. The reagent “(LiZn(TMP)(t-Bu)2

• enabled such reagents to perform special metallation reactions that cannot be reproduced by either of the single-metal components that constitute the mixed-metal reagent. While the alkali metal component is essential for the synergic metallation to follow its course, it is the less electropositive zinc

Intramolecular hydroxycarbene C–H-insertion: The curious case of (o-methoxyphenyl)hydroxycarbene

• Dennis Gerbig,
• David Ley,
• Hans Peter Reisenauer and
• Peter R. Schreiner

Beilstein J. Org. Chem. 2010, 6, 1061–1069, doi:10.3762/bjoc.6.121

• was computed to be 262 kcal mol–1, which is comparable to those of alkali metal hydroxides, this seems a viable possibility. Conclusion The formation of a 2,3-dihydrobenzofuran derivative from carbene 5 in the gas phase is the first C–H insertion reaction observed for a hydroxycarbene derivative

Molecular recognition of organic ammonium ions in solution using synthetic receptors

• Andreas Späth and
• Burkhard König

Beilstein J. Org. Chem. 2010, 6, No. 32, doi:10.3762/bjoc.6.32

Synthesis and properties of calix[4]arene telluropodant ethers as Ag⁺ selective sensors and Ag⁺, Hg²⁺ extractants

• Yang Lu,
• Yuanyuan Li,
• Song He,
• Yan Lu,
• Changying Liu,
• Xianshun Zeng and
• Langxing Chen

Beilstein J. Org. Chem. 2009, 5, No. 59, doi:10.3762/bjoc.5.59

• selectivity coefficients for Ag+ cations were investigated against alkali metal, alkaline-earth metal, lead, ammonium ions and some transition metal ions using the fixed interference method (FIM) [54][55]. Firstly, the response characteristics of Ag+-ISEs based on different ionophores were tested. It was