Mechanistic studies of the solvolysis of alkanesulfonyl and arenesulfonyl halides

• Malcolm J. D’Souza and
• Dennis N. Kevill

Beilstein J. Org. Chem. 2022, 18, 120–132, doi:10.3762/bjoc.18.13

• values are from [56] and [62]. Organic reactions where the breaking of a C–X bond involves the formation of a high energy ion-pair intermediate. The chemical structures for the 1-adamantyl substrate, 2-adamantyl substrate, and the S-methyldibenzothiophenium ion (MeDBTh+). In the 1- and 2-substituted

Nucleofugal behavior of a β-shielded α-cyanovinyl carbanion

• Rudolf Knorr and
• Barbara Schmidt

Beilstein J. Org. Chem. 2018, 14, 3018–3024, doi:10.3762/bjoc.14.281

• ). Preparation and cleavage of the adduct 18 of fluoren-9-one (15). Proton transfer from dicyclopropyl ketone (19) to 2Li. Metal-free release of the carbanion unit in 25 and its seizure by t-BuCH=O (→ 7); Bu = n-butyl. Supporting Information Supporting Information File 336: Ion-pair intermediate through

Stereochemical outcomes of C–F activation reactions of benzyl fluoride

• Neil S. Keddie,
• Pier Alexandre Champagne,
• Justine Desroches,
• Jean-François Paquin and
• David O'Hagan

Beilstein J. Org. Chem. 2018, 14, 106–113, doi:10.3762/bjoc.14.6

• (C) ion pairs. The partial racemization observed in Table 3 suggests that the solvent-separated ion-pair intermediate (C) is most likely the reactive species, as it would naturally lead to a partial racemization of the substrate stereocenter. When the activator was changed from HFIP to a mixed system

Strategies toward protecting group-free glycosylation through selective activation of the anomeric center

• A. Michael Downey and
• Michal Hocek

Beilstein J. Org. Chem. 2017, 13, 1239–1279, doi:10.3762/bjoc.13.123

• worked well with not only simple aliphatic and phenolic alcohols but also with amino acids and steroid alcohols (Figure 1). The authors posit that the stereoselectivity can be rationalized by an oxycarbenium/BF3-coordinated 3-bromo-2-pyridyloxy ion-pair intermediate that is displaced by the alcohol in an

Microsolvation and sp²-stereoinversion of monomeric α-(2,6-di-tert-butylphenyl)vinyllithium as measured by NMR

• Rudolf Knorr,
• Monika Knittl and
• Eva C. Rossmann

Beilstein J. Org. Chem. 2014, 10, 2521–2530, doi:10.3762/bjoc.10.263

• pair intermediate; monomeric alkenyllithiums; pseudoactivation parameters; sp2-stereoinversion mechanism; THF catalysis; Introduction Organolithium compounds tend to aggregate in solution unless the structure of their carbanionic part favors the nonaggregated (monomeric) species [2]. For example

• with the transient immobilization of one additional THF ligand, followed by stereoinversion of the quasi-sp2-hybridized carbanionic center in cooperation with a “conducted tour” migration of Li+(THF)4 along the α-aryl group within the solvent-separated ion pair. Keywords: 13C,6Li NMR coupling; ion

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

• from a surrounding water molecule to form Me(H)C(OH)-NH3+ and a remaining OH− anion in the surrounding. They form an ion pair 3 [Me(H)C(OH)-NH3+ and OH−]. Next, the hydroxide ion catches a proton from HCN through the transition state TS3/4 to afford a more stable ion-pair intermediate 4 [Me(H)C(OH)-NH3

• approach of CN− to 4 concomitantly take place with a Walden inversion. The transition state TS4/8 was successfully located; see Figure 1. However, this pathway needs a large energy barrier of 58.8 = [+51.3 − (−7.5)] kcal/mol, indicating that it is difficult to occur. Starting from the ion-pair intermediate