The chemistry of amine radical cations produced by visible light photoredox catalysis

• Jie Hu,
• Jiang Wang,
• Theresa H. Nguyen and
• Nan Zheng

Beilstein J. Org. Chem. 2013, 9, 1977–2001, doi:10.3762/bjoc.9.234

• . In 2011, Rueping and coworkers described a dual catalytic system combining photoredox and Lewis base catalysis for the functionalization of C–H bonds α to the nitrogen atom of N-aryltetrahydroisoquinoline 13 (Scheme 8) [65]. In the presence of a Lewis base, a ketone is converted to enamine

• nucleophile 28 in situ, which is then added to photogenically formed iminium ion 27 to yield the Mannich product 23. The Mannich reaction was sluggish without the Lewis base, and a side reaction, formation of the oxidized isoquinoline, became significant. The choice of Lewis base was found to be also crucial

• . Oxidative functionalization of N-aryltetrahydroisoquinolines using Eosin Y. Synthetic and mechanistic studies of Eosin Y-catalyzed aza-Henry reaction. Oxidative functionalization of N-aryltetrahydroisoquinolines using RB and GO. Merging Ru-based photoredox catalysis and Lewis base catalysis for the Mannich

Asymmetric allylic alkylation of Morita–Baylis–Hillman carbonates with α-fluoro-β-keto esters

• Lin Yan,
• Zhiqiang Han,
• Bo Zhu,
• Caiyun Yang,
• Choon-Hong Tan and
• Zhiyong Jiang

Beilstein J. Org. Chem. 2013, 9, 1853–1857, doi:10.3762/bjoc.9.216

• introduction of fluorine atoms in molecules has become one of the most exciting and intense research areas in the recent years. Lewis base-catalyzed asymmetric allylic alkylations (AAA) of Morita–Baylis–Hillman (MBH) adducts [5][6], such as acetates and carbonates, have become an attractive option to access

• Lewis base catalysts (Table 1). First, the reaction was conducted in the presence of quinine at 50 °C in dichloroethane (DCE) as the solvent (Table 1, entry 1). The desired adduct 3aa was obtained in 53% yield with poor enantio- and diastereoselectivity. Cinchonine provided similarly poor results (Table

Organocatalyzed enantioselective desymmetrization of aziridines and epoxides

• Ping-An Wang

Beilstein J. Org. Chem. 2013, 9, 1677–1695, doi:10.3762/bjoc.9.192

• -opening product 28 was produced in 94% yield and 91% ee. Therefore, calcium and magnesium phosphate salts of OC-21 proved to be the true catalysts in these processes. The author suggested that these metal phosphates may be generated through the purification of OC-21 on silica gel column. A dual Lewis-base

Organocatalytic asymmetric selenofunctionalization of tryptamine for the synthesis of hexahydropyrrolo[2,3-b]indole derivatives

• Qiang Wei,
• Ya-Yi Wang,
• Yu-Liu Du and
• Liu-Zhu Gong

Beilstein J. Org. Chem. 2013, 9, 1559–1564, doi:10.3762/bjoc.9.177

• . So far, in addition to the chiral-substrate-induced strategy [16], chiral selenylating agents [17][18][19][20][21][22][23][24] are commonly designed for asymmetric selenofunctionalization of carbon–carbon double bonds. In 2010, Denmark and co-workers reported a Lewis base catalyzed asymmetric

• ]. These leading findings indicate that either Lewis base or Brønsted acid shows catalytic activity for the selenofunctionalization reaction. Since chiral phosphoric acids have been shown to be Brønsted acid/Lewis base bifunctional organocatalysts [29][30][31][32][33], we ask whether the chiral BINOL-based

Copper(II)-salt-promoted oxidative ring-opening reactions of bicyclic cyclopropanol derivatives via radical pathways

• Eietsu Hasegawa,
• Minami Tateyama,
• Ryosuke Nagumo,
• Eiji Tayama and
• Hajime Iwamoto

Beilstein J. Org. Chem. 2013, 9, 1397–1406, doi:10.3762/bjoc.9.156

• initially to produce Lewis base–acid complex 7, followed by inner-sphere ET involving elimination of CuOAc and AcOH, which gives cyclopropoxy radical 8. Either external or internal bond cleavage of 8 generates the respective primary alkyl radical 9 or tertiary alkyl radical 10. An equilibrium

• copper(II) salts it is possible to control the reaction pathways followed by radical and ionic intermediates derived from the initially formed Lewis base–acid complexes if the radicals and ions are capable of undergoing different rearrangement reactions. Experimental General: NMR spectra were recorded in

Metal–ligand multiple bonds as frustrated Lewis pairs for C–H functionalization

• Matthew T. Whited

Beilstein J. Org. Chem. 2012, 8, 1554–1563, doi:10.3762/bjoc.8.177

• functionalization schemes. Review Metal–ligand multiple bonds as FLPs Electronic basis for FLP behavior of metal–ligand multiple bonds As mentioned above, most FLPs rely on steric encumbrance to minimize the interaction between an electron-rich Lewis base and an electron-poor Lewis acid. The weakly interacting acid

• –base pair is then capable of activating various substrates by synergistically polarizing bonds, often in a concerted fashion [6][11][12][13][14]. The reaction is favorable, because the small-molecule substrates facilitate a shift in electron density away from the electron-rich Lewis base and toward the

• observed reactivity. M═E FLPs with π-acidic ligands The reverse situation with respect to the metal-based FLPs described above is one in which a coordinatively unsaturated metal acts as a Lewis base and a relatively electropositive π-acidic ligand acts as a Lewis acid. We might expect this situation to be

A quantitative approach to nucleophilic organocatalysis

• Herbert Mayr,
• Sami Lakhdar,
• Biplab Maji and
• Armin R. Ofial

Beilstein J. Org. Chem. 2012, 8, 1458–1478, doi:10.3762/bjoc.8.166

• the formation of the Lewis acid–Lewis base adduct with 18g is 160 times smaller for DABCO (38) than for DMAP (39), i.e., DABCO (38) is a significantly weaker Lewis base than DMAP (39). We have previously discussed that it is the higher reorganization energy for the reaction of DMAP (39) that is

Cation affinity numbers of Lewis bases

• Christoph Lindner,
• Raman Tandon,
• Boris Maryasin,
• Evgeny Larionov and
• Hendrik Zipse

Beilstein J. Org. Chem. 2012, 8, 1406–1442, doi:10.3762/bjoc.8.163

• towards model cations has been quantified. The range of model cations includes the methyl cation as the smallest carbon-centered electrophile, the benzhydryl and trityl cations as models for electrophilic substrates encountered in Lewis base-catalyzed synthetic procedures, and the acetyl cation as a

• substrate model for acyl-transfer reactions. Affinities towards these cationic electrophiles are complemented by data for Lewis-base addition to Michael acceptors as prototypical neutral electrophiles. Keywords: ab initio; cation affinity; Lewis basicity; organocatalysis; proton affinity; Introduction

• -catalyzed processes, affinity data towards carbon electrophiles have only recently been adopted as tools for the assessment of Lewis base reactivity [4]. This is mainly due to the scarcity of accurate experimentally measured or theoretically calculated data. The performance of various theoretical methods to

Organocatalysis

• Benjamin List

Beilstein J. Org. Chem. 2012, 8, 1358–1359, doi:10.3762/bjoc.8.156

• -molecular-weight organic compounds, in which a metal is not part of the active principle. Organocatalysts donate or remove electrons or protons as their activation mode, hence defining four distinct subareas: Lewis base and Lewis acid catalysis on the one hand, and Brønsted base and Brønsted acid catalysis

Organocatalytic asymmetric allylic amination of Morita–Baylis–Hillman carbonates of isatins

• Hang Zhang,
• Shan-Jun Zhang,
• Qing-Qing Zhou,
• Lin Dong and
• Ying-Chun Chen

Beilstein J. Org. Chem. 2012, 8, 1241–1245, doi:10.3762/bjoc.8.139

• investigation of a Lewis base catalyzed asymmetric allylic amination of Morita–Baylis–Hillman carbonates derived from isatins afforded an electrophilic pathway to access multifunctional oxindoles bearing a C3-quaternary stereocenter, provided with good to excellent enantioselectivity (up to 94% ee) and in high

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

• 10.3762/bjoc.8.5 Abstract N,N-Diisopropyl-2-propylbenzamide 6-H undergoes lateral deprotonation by t-BuLi in the presence of the Lewis base PMDTA (N,N,N′,N″,N″-pentamethyldiethylenetriamine) to give a benzyllithium 6-Lil·PMDTA that incorporates a trigonal planar secondary carbanion. In the solid state

• the planarity of the deprotonated carbon centre and the bonding pattern in the organic anion seen in the PMDTA complex are retained. DFT analysis corroborates both the short distance between aromatic ring and carbanion centre and the unperturbed nature of aromaticity in 6-Lil·L (L = Lewis base). The

• observation of two structure-types for the carbanion in solution is explained theoretically and by NMR spectroscopy in terms of cis and trans isomerism imparted by partial double bond character in the arene–(α-C) bond. Keywords: directed metallation; Lewis base; ligand effects; lithium; secondary carbanion

Sexithiophenes as efficient luminescence quenchers of quantum dots

• Christopher R. Mason,
• Yang Li,
• Paul O’Brien,
• Neil J. Findlay and
• Peter J. Skabara

Beilstein J. Org. Chem. 2011, 7, 1722–1731, doi:10.3762/bjoc.7.202

• represents molecules with (1a,b) and without (2a,b) a Lewis base functionality for quantum-dot surface coordination, with a view to determining whether structural complexity is required to achieve nanoparticle–sexithiophene electronic interactions. Results and Discussion Synthesis The preparation of

• ) core/shell quantum dots was conducted to determine the effect of the Lewis base group in sexithiophenes 1a and 1b. The quantum dot CdSe core was prepared by the method of Cumberland et al. [25], and the ZnS shell was added using the dithiocarbamate precursor Zn(S2CNMeHex)2 [26]. The resulting dots

• not be a result of Förster energy transfer. The effect of each of the corresponding sexithiophenes with or without a Lewis base group (1 or 2) was then studied by preparing separate stock solutions of quantum dots and sexithiophenes 1b or 2b, of known concentration. A fixed amount of quantum dot

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

• dialkyl(aryl) sodium zincate ((TMEDA)Na(o-C6H4-NMe2)t-BuZnt-Bu), reminiscent of the lithium congeners ((THF)3Li(o-C6H4-OMe)t-BuZnt-Bu) and ((PMDETA)Li(o-C6H4-OMe)t-BuZnt-Bu) prepared by co-complexation reactions of lithiated anisole with t-Bu2Zn and the relevant Lewis base [27]. The metallation

The allylic chalcogen effect in olefin metathesis

• Yuya A. Lin and
• Benjamin G. Davis

Beilstein J. Org. Chem. 2010, 6, 1219–1228, doi:10.3762/bjoc.6.140

• is likely due to the soft nature of sulfur as a Lewis base making it a better ligand for ruthenium than the oxygen atom in Hoveyda–Grubbs second-generation catalyst 4. It is currently unclear whether a similar effect would be observed for phosphine-containing metathesis catalysts such as 1a and 2. As

Kinetics and mechanism of vanadium catalysed asymmetric cyanohydrin synthesis in propylene carbonate

• Michael North and
• Marta Omedes-Pujol

Beilstein J. Org. Chem. 2010, 6, 1043–1055, doi:10.3762/bjoc.6.119

• that Lewis base catalysis made a much greater contribution to the overall catalytic activity of VO(salen)NCS in propylene carbonate than in dichloromethane. Keywords: cyanohydrin; Hammett; kinetics; propylene carbonate; vanadium; Introduction The last 15 years have witnessed an explosion of activity

• Lewis base catalysis are known to be involved in the catalytic cycle, the latter possibly involving the isothiocyanate counterion [52]. Despite their many favourable properties, there is one drawback associated with catalysts 1 and 2; they exhibit highest activity and highest enantioselectivity in

• , which allow differences in the relative importance of Lewis acid and Lewis base catalysis between reactions carried out in dichloromethane and propylene carbonate to be elucidated. Results and Discussion Synthetic Studies Initially, the compatibility of catalysts 1 and 2 with propylene carbonate was

EPR and pulsed ENDOR study of intermediates from reactions of aromatic azides with group 13 metal trichlorides

• Giorgio Bencivenni,
• Riccardo Cesari,
• Daniele Nanni,
• Hassane El Mkami and
• John C. Walton

Beilstein J. Org. Chem. 2010, 6, 713–725, doi:10.3762/bjoc.6.84

• halide to the starting azide should produce the Lewis base–acid adduct 12 that could undergo reduction by ET from more azide to afford, after nitrogen loss, the metal-coordinated aminyl radical 13 together with the ArN3+• radical cation. Aminyl radical 13 could then abstract an H-atom from solvent RH (or

CAAC Boranes. Synthesis and characterization of cyclic (alkyl) (amino) carbene borane complexes from BF₃ and BH₃

• Julien Monot,
• Louis Fensterbank,
• Max Malacria,
• Emmanuel Lacôte,
• Steven J. Geib and
• Dennis P. Curran

Beilstein J. Org. Chem. 2010, 6, 709–712, doi:10.3762/bjoc.6.82

• formed in situ according to 1H and 11B NMR analysis, but did not survive the workup conditions. These results set the stage for further studies of the chemistry of CAAC boranes. Keywords: borane Lewis acid Lewis base complexes; carbene–borane complexes; cyclic (alkyl) (amino) carbenes; N-heterocyclic

• carbenes; stable carbenes; Introduction Lewis acid/Lewis base complexes of N-heterocyclic carbenes and boranes (NHC–boranes) are readily prepared from NHC’s and boranes by direct complexation [1][2][3][4]. Unlike many other classes of Lewis base complexes of boranes with neutral molecules (ethers

The subtle balance of weak supramolecular interactions: The hierarchy of halogen and hydrogen bonds in haloanilinium and halopyridinium salts

• Kari Raatikainen,
• Massimo Cametti and
• Kari Rissanen

Beilstein J. Org. Chem. 2010, 6, No. 4, doi:10.3762/bjoc.6.4

• (Lewis base, nucleophilic) [20]. According to this definition, halogen bonding covers a vast family of non-covalent interactions, and a very wide range of interaction energies [20]. Concurrently with the development of practical applications and experimental studies on halogen bonding systems

Diastereoselective functionalisation of benzo-annulated bicyclic sultams: Application for the synthesis of cis-2,4-diarylpyrrolidines

• Susan Kelleher,
• Pierre-Yves Quesne and
• Paul Evans

Beilstein J. Org. Chem. 2009, 5, No. 69, doi:10.3762/bjoc.5.69

• mechanism of stabilisation has been suggested in which one of the sulfonyl oxygen atoms may act as a Lewis base and in doing so stabilise the positive charge [22][23]. Inspection of the X-ray structure obtained for compounds 7a and 7b (not shown) indicates that this stabilisation mechanism may be possible

Continuous flow enantioselective arylation of aldehydes with ArZnEt using triarylboroxins as the ultimate source of aryl groups

• Julien Rolland,
• Xacobe C. Cambeiro,
• Carles Rodríguez-Escrich and
• Miquel A. Pericàs

Beilstein J. Org. Chem. 2009, 5, No. 56, doi:10.3762/bjoc.5.56

• Lewis base (O) and Lewis acid (B) character that could coordinate the reactant molecules (aldehyde and arylethylzinc) in an arrangement suitable for reaction. In this sense, it is noteworthy that when control experiments were done by using resin 2 under batch conditions with the Ph2Zn/Et2Zn combination