Quantification of the nucleophilic reactivity of nicotine

Rate and equilibrium constants of the reactions of nicotine and structurally related compounds with benzhydrylium ions have been determined UV-Vis spectroscopically using stopped-flow and laser-flash techniques. The pyridine nitrogen of nicotine was identified as the site of thermodynamically and kinetically controlled attack. Quantum chemical calculations showed that the introduction of a pyrid-3-yl moiety into the 2-position of N-methylpyrrolidine (to give nicotine) reduces the Lewis basicity of the pyrrolidine ring by 24kJmol(-1), whereas the analogous introduction of a phenyl ring decreases this quantity by only 11kJmol(-1)

Ammonium Pertechnetate in Mixtures of Trifluoromethanesulfonic Acid and Trifluoromethanesulfonic Anhydride

Ammonium pertechnetate reacts in mixtures of trifluoromethanesulfonic anhydride and trifluoromethanesulfonic acid under final formation of ammonium pentakis(trifluoromethanesulfonato)oxidotechnetate(V), (NH$_{4}$)$_{2}$ [TcO(OTf) $_{5}$]. The reaction proceeds only at exact concentrations and under the exclusion of air and moisture via pertechnetyl trifluoromethanesulfonate, [TcO$_{3}$(OTf)], and intermediate Tc$^{VI}$ species. $^{99}$Tc nuclear magnetic resonance (NMR) has been used to study the Tc$^{VII}$ compound and electron paramagnetic resonance (EPR), $^{99}$Tc NMR and X-ray absorption near-edge structure (XANES) experiments indicate the presence of the reduced technetium species. In moist air, (NH$_{4}$)2[TcO(OTf)5] slowly hydrolyses under formation of the tetrameric oxidotechnetate(V) (NH$_{4}$)$_{4}$ [{TcO(TcO$_{4}$)$_{4}$}$_{4}$] ⋅10 H$_{2}$O. Single-crystal X-ray crystallography was used to determine the solid-state structures. Additionally, UV/Vis absorption and IR spectra as well as quantum chemical calculations confirm the identity of the species

Iodine-Catalyzed Carbonyl-Alkyne Metathesis Reactions

The reaction between aldehydes or ketones and alkynes –the carbonyl-alkyne metathesis– constitutes a very useful strategy for the synthesis of ,-unsaturated carbonyls. We now demonstrate that iodine is a highly efficient catalyst for both the intra- and intermolecular metathesis reaction in very small concentrations (0.1–1 mol%). Our protocol outperforms other catalytic systems, is operationally very simple, cheap, metal-free, and tolerates a large variety of functional groups (e.g., –CN, –CO2Me, –Br, –OH) at very low catalyst loadings. We can furthermore show that iodine-catalyzed carbonyl-alkyne metatheses can be combined with other iodine-catalyzed reactions in one-pot procedures to afford larger and more complex molecular structures. Finally, our mechanistic studies indicate that the iodonium ion is the active catalyst under the reaction conditions

sigma-Hole Interactions in Catalysis

Noncovalent interactions like halogen, chalcogen, and pnictogen bonding are known for a very long time. During the last decade, these interactions have found different applications in catalysis. These forces are often called sigma-hole interactions which can be explained by the anisotropic distribution of the electron density around these atoms. In this MiniReview, we will present recent applications of halogen, chalcogen, and pnictogen bonding in catalysis and discuss experimental and computational investigations to gain more insights into the underlying mechanisms

Milestones of the 1,3‐Dipolar Cycloaddition

The concept of 1,3‐dipolar cycloadditions was presented by Rolf Huisgen 60 years ago. Previously unknown reactive intermediates, for example azomethine ylides, were introduced to organic chemistry and the (3+2) cycloadditions of 1,3‐dipoles to multiple‐bond systems (Huisgen reaction) developed into one of the most versatile synthetic methods in heterocyclic chemistry. In this Review, we present the history of this research area, highlight important older reports, and describe the evolution and further development of the concept. The most important mechanistic and synthetic results are discussed. Quantum‐mechanical calculations support the concerted mechanism always favored by R. Huisgen; however, in extreme cases intermediates may be involved. The impact of 1,3‐dipolar cycloadditions on the click chemistry concept of K. B. Sharpless will also be discussed

The Huisgen Reaction: Milestones of the 1,3-Dipolar Cycloaddition

The concept of 1,3-dipolar cycloadditions was presented by Rolf Huisgen 60 years ago. Previously unknown reactive intermediates, for example azomethine ylides, were introduced to organic chemistry and the (3+2) cycloadditions of 1,3-dipoles to multiple-bond systems (Huisgen reaction) developed into one of the most versatile synthetic methods in heterocyclic chemistry. In this Review, we present the history of this research area, highlight important older reports, and describe the evolution and further development of the concept. The most important mechanistic and synthetic results are discussed. Quantum-mechanical calculations support the concerted mechanism always favored by R. Huisgen; however, in extreme cases intermediates may be involved. The impact of 1,3-dipolar cycloadditions on the click chemistry concept of K. B. Sharpless will also be discussed

Radical addition of ketones and cyanide to olefins via acid catalyzed formation of intermediate alkenyl peroxides

A Bronsted acid catalyzed method was developed for the synthesis of.-cyanoketones from sulfonyl cyanides, olefins and ketones. The reaction is believed to proceed via intermediate formation of alkenyl peroxides by condensation of ketones with tert-butylhydroperoxide. These unstable compounds decompose by homolytic O-O bond cleavage, generating ketone-derived radicals which add to the olefins and generate the final products after reaction with the sulfonyl cyanide, thereby forming two new C-C bonds. A range of different ketones and olefins can be used, including steroidal ketones and simple alkyl olefins. The products can be further transformed to substituted lactones and piperidines, including a tetracyclic one. This reaction can thus be utilized to gain access to complex molecules from simple starting materials in only a few synthetic steps