Atherton–Todd reaction: mechanism, scope and applications

• Stéphanie S. Le Corre,
• Mathieu Berchel,
• Hélène Couthon-Gourvès,
• Jean-Pierre Haelters and
• Paul-Alain Jaffrès

Beilstein J. Org. Chem. 2014, 10, 1166–1196, doi:10.3762/bjoc.10.117

• reactions as those reported above, phosphoramidates, prepared by AT reactions, can also act as an organocatalyst. Indeed, with the strongly polarized P–O bond on one hand, and the P–N or P–NH bond on the other hand phosphoramides are good Lewis bases [96][97][98]. Hexamethylphosphoric triamide (HMPA) (or

Garner’s aldehyde as a versatile intermediate in the synthesis of enantiopure natural products

• Mikko Passiniemi and
• Ari M.P. Koskinen

Beilstein J. Org. Chem. 2013, 9, 2641–2659, doi:10.3762/bjoc.9.300

• in the presence of 100 mol % of TiCl4 in THF gave a 5:1 (anti/syn) mixture of adducts 20 and 21. Tetrahydrofuran coordinates quite strongly to Lewis acids, which increases the electron density at the metal atom. This lowers the metal atom’s ability to coordinate to other Lewis bases, such as the

True and masked three-coordinate T-shaped platinum(II) intermediates

• Manuel A. Ortuño,
• Salvador Conejero and
• Agustí Lledós

Beilstein J. Org. Chem. 2013, 9, 1352–1382, doi:10.3762/bjoc.9.153

• allows the formation of an agostic contact. Treatment of A8 with Lewis bases also removes the agostic interaction, generating the adduct complex. Natural Bond Orbital (NBO) and Atoms In Molecules (AIM) calculations on complexes A1, A2b, A5b and A7 classified the Pt···H–C contacts as agostic interactions

Enantioselective reduction of ketoimines promoted by easily available (S)-proline derivatives

• Martina Bonsignore,
• Maurizio Benaglia,
• Laura Raimondi,
• Manuel Orlandi and
• Giuseppe Celentano

Beilstein J. Org. Chem. 2013, 9, 633–640, doi:10.3762/bjoc.9.71

• 10.3762/bjoc.9.71 Abstract The behavior of readily synthesized and even commercially available (S)-proline derivatives, was studied in the trichlorosilane-mediated reduction of ketoimines. A small library of structurally and electronically modified chiral Lewis bases was considered; such compounds were

• studies were also performed in order to elucidate the origin of the stereoselection. Keywords: chiral prolines; imine reduction; Lewis bases; organocatalysis; trichlorosilane; Introduction The reaction with stoichiometric amounts of trichlorosilane in the presence of a chiral catalyst is a well

• -established methodology to perform enantioselective reductions of carbon nitrogen double bonds [1]. In the past decade different classes of enantiomerically pure Lewis bases have been developed, including N-formyl derivatives, oxazolines, imidazole derivatives, sulfonamides and picolinamides [2][3]. Some of

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

• –200 kJ mol–1) Lewis bases. While structurally analogous imidazolylidenes and imidazolidinylidenes have comparable nucleophilicities and Lewis basicities, the corresponding deoxy Breslow intermediates differ dramatically in reactivity. The thousand-fold higher nucleophilicity of 2-benzylidene

• NHCs, 41, 42, and 43, react quantitatively with the quinone methide 18k, while none of the other Lewis bases, despite their similar nucleophilicities, gives an adduct. The resulting conclusion, that all NHCs are significantly stronger Lewis bases than PPh3 (10b), DMAP (39), and DABCO (38), is confirmed

• by quantum chemical calculations: The methyl cation affinities (MCAs) of the three carbenes 41–43 are 100–200 kJ mol–1 higher than those of the other Lewis bases in Figure 23 [96]. As the carbenes 41 and 42 have almost identical nucleophilicities and Lewis basicities, the question arose as to why

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

• Christoph Lindner Raman Tandon Boris Maryasin Evgeny Larionov Hendrik Zipse Department of Chemistry, Ludwigs-Maximilians-Universität München, Butenandstr. 5–13, D-81377 München, Germany 10.3762/bjoc.8.163 Abstract Using selected theoretical methods the affinity of a large range of Lewis bases

• Discussion Methyl cation affinities (MCA) The methyl cation (CH3+) is the smallest carbocation which is useful as a chemical probe for Lewis bases. The respective methyl cation affinity of a given Lewis base (LB) is obtained as the reaction enthalpy at 298.15 K and 1 bar pressure for the reaction shown in

• equation 1a for a neutral Lewis base and in equation 1b for an anionic base (Scheme 1). This definition is in analogy to that for proton affinities (PA) and implies large positive energies for most of the P- and N-based Lewis bases used in catalytic processes. Using pyridine (1) as an example for a weak

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

• presence of different Lewis bases. In contrast to previous work on carbanion formation in the presence of an aromatic N+O directing group, 6-Lil·L dissolves in hydrocarbon media to reveal two structures in solution. Based on previous work and new DFT studies, we ascribe these as being cis (minor) and trans

• between the identity and structure of the tridentate Lewis base and the propensity of the metal and deprotonated α-C centre to interact. In particular, tandem theoretical and NMR spectroscopic studies will seek to elucidate whether polydentate Lewis bases may exhibit dynamic and variable hapticity with

Chiral gold(I) vs chiral silver complexes as catalysts for the enantioselective synthesis of the second generation GSK-hepatitis C virus inhibitor

• María Martín-Rodríguez,
• Carmen Nájera,
• José M. Sansano,
• Abel de Cózar and
• Fernando P. Cossío

Beilstein J. Org. Chem. 2011, 7, 988–996, doi:10.3762/bjoc.7.111

• of the 1,3-DC employing chiral metallic Lewis bases arises from the blockage of one of the prochiral faces [40]. In this way, our results (in terms of DFT calculations) show that there is only one energetically accessible conformation due to the high substitution of the leucine-derived ylide (Figure

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

• established that the asymmetric addition of TMSCN to aldehydes can be catalysed by both Lewis acids and Lewis bases [1]. A Lewis acid catalyst activates the aldehyde by formation of an aldehyde-Lewis acid complex (e.g., 4) whilst a Lewis base catalyst activates the TMSCN through formation of a hypervalent