On the Mechanism of the Dyotropic Expansion of Hydrindanes into Decalins

A combined computational/experimental approach has revealed key mechanistic aspects in a recently reported dyotropic expansion of hydrindanes into decalins. While computer simulations had already anticipated the need for acid catalysis...

Metal-free, visible-light induced enantioselective three-component dicarbofunctionalization and oxytrifluoromethylation of enamines via chiral phosphoric acid catalysis

Using diverse carbon-centered radical precursors and electron-rich (hetero)aromatics and alcohols as nucleophiles, a visible-light driven chiral phosphoric acid (CPA) catalyzed asymmetric intermolecular, three-component radical-initiated dicarbofunctionalization and oxytrifluoromethylation of enamines was...

Concomitant Functionalization of Two Different Ketones by Merging Brønsted Acid Catalysis and Radical Relay Coupling

In previous literature, incorporation of functional groups at the α-position of unactivated carbonyl compounds was mainly restricted to one kind of corresponding precursors. Herein, we report the concomitant functionalization of...

Boron-Based Lewis Acid Catalysis: Challenges and Perspectives

In the last two decades, boron-based catalysis has been gaining increasing traction in the field of organic synthesis. The use of halogenated triarylboranes as main group Lewis acid catalysts is an attractive strategy. It has been applied in a growing number of transformations over the years, where they may perform comparably or even better than the gold standard catalysts. This review discusses methods of borane synthesis and cutting-edge boron-based Lewis acid catalysis, focusing especially on tris(pentafluorophenyl)-borane [B(C6F5)3], and other halogenated triarylboranes, highlighting how boron Lewis acids employed as catalysts can unlock a plethora of unprecedented chemical transformations or improve the efficiency of existing reactions.

Acid-Catalyzed Esterification of Betaines: Theoretical Exploration of the Impact of the Carbon Chain Length on the Reaction Mechanism

Betaine derivatives, especially esters, are compounds of interest for the development of a more sustainable fine chemistry, as they are widely available from biomass and currently produced as side-products from various industries (among which, sugar production). In this publication, we studied the impact of carbon chain length on three considered reaction mechanisms for the esterification of (CH3)3N(CH2)nCO2 betaine (n = 1, 2, 3) with glycerol under acid catalysis. DFT calculations show that the mechanism proposed by Bachmann–Frapper et al. may also be active here, but it can interestingly be seen as an avatar of the former proposition by Watson. Conversely, Ingold’s proposition is in this case too energetically prevented. Overall, lower activation barriers and higher reaction exergonicity are reported, suggesting esterification of longer carbon-chain based betaines is more readily achieved.

Synergistic Brønsted/Lewis Acid Catalyzed Aromatic Alkylation with Unactivated Tertiary Alcohols or Di-tert-Butylperoxide to Synthesize Quaternary Carbon Centers

Dual Brønsted/Lewis acid catalysis involving environmentally benign, readily accessible protic acid and iron promotes site-selective tert-butylation of electron-rich arenes using di-tert-butylperoxide. This transformation inspired the development of a synergistic Brønsted/Lewis acid catalyzed aromatic alkylation that fills a gap in the Friedel–Crafts reaction literature by employing unactivated tertiary alcohols as alkylating agents, leading to new quaternary carbon centers. Corroborated by DFT calculations, the Lewis acid serves a role in enhancing the acidity of the Brønsted acid. The use of non-allylic, non-benzylic, and non-propargylic tertiary alcohols represents an underexplored area in Friedel–Crafts reactivity.

Access to chiral 1-aminoindene derivatives by asymmetric Brønsted acid catalysis

Asymmetric organocatalysis is emerging as an elegant tool for accelerating chemical reactions and creating specific types of molecules. Chiral Brønsted acid catalysis is an important area of organocatalysis. Recently we described a chiral Brønsted acid (N-triflyl phosphoramide) catalyzed intramolecular iminium ion cyclization reaction of 2-alkenylbenzaldimines for the synthesis of chiral 1-aminoindenes and tetracyclic 1-aminoindanes in good yields and high enantioselectivities. The obtained 1-aminoindene can be utilized as useful synthetic intermediate for synthesis of (S)-rasagiline, an effective drug for the symptomatic treatment of Parkinson's disease. And the obtained tetracyclic 1-aminoindanes are the skeleton of homoisoflavanoid natural products such as brazilin.