LongLarf

Dearomative cycloaddition reactions represent an ideal means of converting flat arenes into three-dimensional architectures of increasing interest in medicinal chemistry. Quinolines, isoquinolines, and quinazolines, despite containing latent diene and alkene subunits, are scarcely applied in cycloaddition reactions because of the inherent low reactivity of aromatic systems and selectivity challenges. Here, we disclose an energy transfer–mediated, highly regio- and diastereoselective intermolecular [4 + 2] dearomative cycloaddition reaction of these bicyclic azaarenes with a plethora of electronically diverse alkenes. This approach bypasses the general reactivity and selectivity issues, thereby providing various bridged polycycles that previously have been inaccessible or required elaborate synthetic efforts. Computational studies with density functional theory elucidate the mechanism and origins of the observed regio- and diastereoselectivities.

Publication date: 4 June 2021

Source: Tetrahedron, Volume 89

Author(s): Noboru Hayama, Yusuke Kobayashi, Yoshiji Takemoto

Synlett
DOI: 10.1055/a-1390-9065

Photoredox catalysis has proven to be a powerful tool in synthetic organic chemistry. The rational design of photosensitizers with improved photocatalytic performance constitutes a major advancement in photoredox organic transformations. This review summarizes the fundamental ground-state and excited-state photophysical and electrochemical attributes of molecular photosensitizers, which are important determinants of their photocatalytic reactivity.
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Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart, Germany

Article in Thieme eJournals:
Table of contents  |  Abstract  |  Full text

Publication date: 8 April 2021

Source: Chem, Volume 7, Issue 4

Author(s): Marius D.R. Lutz, Valentina C.M. Gasser, Bill Morandi

The hydrogenation of secondary carboxylic acid amides by combined phosphane oxide and frustrated Lewis pair catalysis is described. The reaction proceeds under mild conditions and displays excellent functional group tolerance. Kinetic and quantum-chemical experiments support the autoinduced catalytic cycle with chloride as active Lewis base for the hydrogen activation.

Abstract

The metal-free catalytic hydrogenation of secondary carboxylic acid amides is developed. The reduction is realized by two new catalytic reactions. First, the amide is converted into the imidoyl chloride by triphosgene (CO(OCCl₃)₂) using novel phosphorus(V) catalysts. Second, the in situ generated imidoyl chlorides are hydrogenated in high yields by an FLP-catalyst. Mechanistic and quantum mechanical calculations support an autoinduced catalytic cycle for the hydrogenation with chloride acting as unusual Lewis base for FLP-mediated H₂-activation.

Porous ionic liquids based on the ZIF-8 metal–organic framework and on phosphonium acetate or levulinate salts were prepared. These show an increased capacity to absorb carbon dioxide at low pressures. Porous suspensions based on phosphonium levulinate ionic liquid absorb reversibly 103 % more carbon dioxide per mass than pure ZIF-8 at 1 bar and 303 K.

Abstract

Porous ionic liquids are non-volatile, versatile materials that associate porosity and fluidity. New porous ionic liquids, based on the ZIF-8 metal–organic framework and on phosphonium acetate or levulinate salts, were prepared and show an increased capacity to absorb carbon dioxide at low pressures. Porous suspensions based on phosphonium levulinate ionic liquid absorb reversibly 103 % more carbon dioxide per mass than pure ZIF-8 at 1 bar and 303 K. We show how the rational combination of MOFs with ionic liquids can greatly enhance low pressure CO₂ absorption, paving the way towards a new generation of high-performance, readily available liquid materials for effective low pressure carbon capture.

Prepare for trouble—and make it double: A organoselenium-catalysed, regiospecific para-hydroxylation starting from N-aryl hydroxamic acids through double [2,3]-sigmatropic rearrangement to form para-aminophenols was developed. This operationally easy reaction delivers useful para-aminophenol building blocks on small and large scales and its mechanism is supported through quantum chemical calculations as well as labeling experiments.

Abstract

A selenium-catalysed para-hydroxylation of N-aryl-hydroxamic acids is reported. Mechanistically, the reaction comprises an N−O bond cleavage and consecutive selenium-induced [2,3]-rearrangement to deliver para-hydroxyaniline derivatives. The mechanism is studied through both ¹⁸O-crossover experiments as well as quantum chemical calculations. This redox-neutral transformation provides an unconventional synthetic approach to para-aminophenols.