Novel Brønsted Acid Catalyzed C-C Bond Activation and α-Alkylation of Ketones.

A novel approach for the α-alkylation of ketones was developed using Brønsted acid-catalyzed C-C bond cleavage. Both aromatic and aliphatic ketones reacted smoothly with 2-substituted 1,3-diphenylpropane-1,3-diones to afford α-alkylation products with high yields and with excellent regioselectivity, in which the 1,3-dicarbonyl group acted as a leaving group in the presence of the catalyst TfOH. Mechanism experiments showed that the ß-C-C bond cleavage of diketone and the shift of the equilibrium towards the enol formation from ketone are driving forces that induce the desired products.

ORGANOMETALLIC GAS-PHASE ION CHEMISTRY AND CATALYSIS: INSIGHTS INTO THE USE OF METAL CATALYSTS TO PROMOTE SELECTIVITY IN THE REACTIONS OF CARBOXYLIC ACIDS AND THEIR DERIVATIVES.

Carboxylic acids are valuable organic substrates as they are widely available, easy to handle, and exhibit structural and functional variety. While they are used in many standard synthetic protocols, over the past two decades numerous studies have explored new modes of metal-mediated reactivity of carboxylic acids and their derivatives. Mass spectrometry-based studies can provide fundamental mechanistic insights into these new modes of reactivity. Here gas-phase models for the following catalytic transformations of carboxylic acids and their derivatives are reviewed: protodecarboxylation; dehydration; decarbonylation; reaction as coordinated bases in C-H bond activation; remote functionalization and decarboxylative C-C bond coupling. In each case the catalytic problem is defined, insights from gas-phase studies are highlighted, comparisons with condensed-phase systems are made and perspectives are reached. Finally, the potential role for mechanistic studies that integrate both gas- and condensed-phase studies is highlighted by recent studies on the discovery of new catalysts for the selective decomposition of formic acid and the invention of the new extrusion-insertion class of reactions for the synthesis of amides, thioamides, and amidines. © 2020 John Wiley & Sons Ltd. Mass Spec Rev.

Reversible C=C Bond Activation by an Intramolecularly Coordinated Antimony(I) Compound.

The reaction of N,C,N-chelated stibinidene ArSb (1) (Ar=C6 H3 -2,6-(CH=NtBu)2 ) with selected N-alkyl/aryl-maleimides RN(C(O)CH)2 (R=Me, tBu, Ph) gave the addition products with bridged bicyclic [2.2.1] structure containing an antimony atom at the bridgehead position, fused with a 6-membered benzene and a 5-membered N-alkyl/aryl-pyrrolidine ring. These compounds were completely characterized. More importantly, additional studies showed that these reactions are reversible in solution, thereby representing an unprecedented reversible activation of a C=C bond by an antimony(I) compound.

Observation of Spontaneous C=C Bond Breaking in the Reaction between Atomic Boron and Ethylene in Solid Neon.

A ground-state boron atom inserts into the C=C bond of ethylene to spontaneously form the allene-like compound H2 CBCH2 on annealing in solid neon. This compound can further isomerize to the propyne-like HCBCH3 isomer under UV light excitation. The observation of this unique spontaneous C=C bond insertion reaction is consistent with theoretical predictions that the reaction is thermodynamically exothermic and kinetically facile. This work demonstrates that the stronger C=C bond, rather than the less inert C-H bond, can be broken to form organoboron species from the reaction of a boron atom with ethylene even at cryogenic temperatures.

Radical α-C-H Cyclobutylation of Aniline Derivatives.

A catalytic system has been developed for the direct alkylation of α-C-H bonds of aniline derivatives with strained C-C σ-bonds. This method operates through a photoredox mechanism in which oxidative formation of aminoalkyl radical intermediates enables addition to a bicyclobutane derivative, giving rise to α-cyclobutyl N-alkylaniline products. This mild system proceeds through a redox- and proton-neutral mechanism and is operational for a range of substituted arylamine derivatives.

A QM/MM study on ethene and benzene oxidation using silica-supported chromium trioxide.

Oxidation of ethene and benzene by chromium oxide (CrO3) supported on silica (SiO2) was investigated by employing hybrid quantum mechanics/molecular mechanics (QM/MM) model calculations. Various mechanistic possibilities, such as C-H or C=C bond activation of hydrocarbons, were investigated in detail for the reaction of ethene and benzene with CrO3 grafted on a silica surface. While activation of the C-H bond leads to the formation of alcohol, epoxide is obtained via C=C bond activation. The complete reaction routes for the formation of each product were traced and found to be exothermic. Thermochemical analysis were performed to predict temperature conditions for the reaction to be feasible in a forward direction. The study provides conclusive evidence to aid experimentalists for further research on oxidation of hydrocarbons using silica-supported metal oxides. Graphical abstract Oxidation of ethene and benzene using silica-supported chromium trioxide.