Lewis Acid Catalyzed Inverse Electron-Demand Diels−Alder Reaction of 1,2-Diazines

Kessler, Simon N.; Wegner, Hermann A.

doi:10.1021/ol101701z

Cited by 104 publications

(72 citation statements)

References 47 publications

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“…The rigid geometry of phthalazine ( 7 ) and the defined position of the nitrogen atoms made it a perfect candidate for such an investigation. The bis‐borane scaffold 9,10‐dimethyl‐9,10‐dihydroboranthracene ( 10 ) was selected as the catalyst . It showed the desired performance in the computational screening and is synthetically easily accessible .…”

Section: Bidentate Lewis Acid Catalysis By the Activation Of The Starmentioning

confidence: 99%

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Bis‐Boron Compounds in Catalysis: Bidentate and Bifunctional Activation

Schweighauser

Wegner

2016

Chemistry A European J

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The development of metal-free catalysts as an alternative to the use of transition metals has gained tremendous interest in the past. In catalysis, Lewis acidity is one of the major principles used for the activation of organic compounds. Improving the reactivity and selectivity of Lewis acids by utilizing bidentate interactions was already proposed 50 years ago. Nevertheless, product inhibition due to strong binding has made applications of bidentate Lewis acids challenging for many years. Recently, bis-boron compounds have been found to be very effective and several applications in Diels-Alder reactions, carbon dioxide reduction, and ammonia-borane dehydrogenation were reported. All three transformations are enabled by the catalyst at different stages during the course of the reaction. These new and useful examples illustrate the great potential of the concept.

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Section: Bidentate Lewis Acid Catalysis By the Activation Of The Starmentioning

confidence: 99%

“… a) Computed HOMO and LUMO energies of phthalazine ( 7 ) and complex 11 (optimized on B3LYP/6‐31G*; orbital energies with HF/6‐31G*); b) X‐ray structure of complex 11 (reprinted with permission from ref. Copyright [2011] Wiley‐VCH Verlag GmbH & Co).…”

Section: Bidentate Lewis Acid Catalysis By the Activation Of The Starmentioning

confidence: 99%

Bis‐Boron Compounds in Catalysis: Bidentate and Bifunctional Activation

Schweighauser

Wegner

2016

Chemistry A European J

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“…[16] ing of the protons. [4] Another mechanistic possibility could be the complexation of the catalyst with the dienophile instead. All of the dienophiles discussed are also electron-rich and usually have heteroatoms that can form Lewis acidLewis base pairs.…”

Section: Mechanistic Investigationsmentioning

confidence: 99%

Bidentate Lewis Acids for the Activation of 1,2‐Diazines – A New Mode of Catalysis

2011

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Bidentate Lewis acids were applied as catalysts for the inverse‐electron‐demand Diels–Alder (IEDDA) reaction of 1,2‐diazines. The concept of catalysis is based on the coordination of the bidentate Lewis acid to both nitrogen atoms of the 1,2‐diazine moiety, thereby reducing the electron density and lowering the energy of the LUMO. This should, according to frontier molecular orbital (FMO) theory, facilitate the cycloaddition step. This new concept was successfully applied to a variety of dienophiles and substituted phthalazine substrates. Careful investigations of the mechanism led to the isolation and characterization of key intermediates; all of which support the presented catalytic cycle.

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“…Because of our success with the diboraanthracene scaffold as ac atalyst for the inverse-electron-demand Diels-Alder reaction, [20,21] we used 9,10-dichlorodiboraanthracene 1 for first experiments on the release of H 2 from AB.W ith its two Lewis acidic sites,ithas adefinite geometry and arather high Lewis acidity owing to the electron-withdrawing effect of the Cl substituents.When 1mol %of1 was added to asolution of AB in THF/diglyme (1:4) at 60 8 8C, vigorous evolution of gas was observed immediately (Scheme 1). Thesolvent mixture is ac ompromise between the solubilities of catalyst 1 and AB and as uitable boiling point to run the reaction for longer periods of time at the given temperature.T he 11 BNMR spectrum of the soluble materials displayed ad oublet at 30.5 ppm and ab road singlet at 25.5 ppm, [22] indicating that borazine and its BN-cross-linked oligomers (polyborazylene) were formed as the main by-products.…”

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confidence: 99%

Metal‐Free Ammonia–Borane Dehydrogenation Catalyzed by a Bis(borane) Lewis Acid

Schweighauser

Hausmann

et al. 2015

Angew Chem Int Ed

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The storage of energy in a safe and environmentally benign way is one of the main challenges of today's society. Ammonia-borane (AB=NH3 BH3 ) has been proposed as a possible candidate for the chemical storage of hydrogen. However, the efficient release of hydrogen is still an active field of research. Herein, we present a metal-free bis(borane) Lewis acid catalyst that promotes the evolution of up to 2.5 equivalents of H2 per AB molecule. The catalyst can be reused multiple times without loss of activity. The moderate temperature of 60 °C allows for controlling the supply of H2 on demand simply by heating and cooling. Mechanistic studies give preliminary insights into the kinetics and mechanism of the catalytic reaction.

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Lewis Acid Catalyzed Inverse Electron-Demand Diels−Alder Reaction of 1,2-Diazines

Abstract: A systematic approach toward Lewis acid catalyzed inverse electron-demand Diels-Alder (IEDDA) reactions of 1,2-diazines is described. The general concept is first investigated by DFT calculations, supported by spectroscopic data, and finally proven in the experiment.

Cited by 104 publications

References 47 publications

Bis‐Boron Compounds in Catalysis: Bidentate and Bifunctional Activation

Bis‐Boron Compounds in Catalysis: Bidentate and Bifunctional Activation

Bidentate Lewis Acids for the Activation of 1,2‐Diazines – A New Mode of Catalysis

Metal‐Free Ammonia–Borane Dehydrogenation Catalyzed by a Bis(borane) Lewis Acid

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