i-Pr2NMgCl·LiCl Enables the Synthesis of Ketones by Direct Addition of Grignard Reagents to Carboxylate Anions

Regioselective synthesis of N-containing polycyclic compounds via radical annulation cyclization of 1,7-dienes with aldehydes

A convenient method for oxidant-promoted radical cascade acylation or decarbonylative alkylation of 1,7-dienes with aldehydes has been established. This method allows for the rapid construction of N-containing polycyclic skeletons in a highly regio- and stereoselective manner. This transformation provides a simple and efficient method for the preparation of a range of tetrahydro-6H-indeno[2,1-c]quinolinone derivatives by sequential formation of three new carbon-carbon bonds. Additionally, this radical cascade cyclization can selectively convert aldehydes into aroyl/primary aliphatic acyl radicals and secondary or tertiary alkyl radicals.

D. dos Santos AC, Kohlhepp SV, Mendoza A. Direct Addition of Grignard Reagents to Aliphatic Carboxylic Acids Enabled by Bulky turbo ‐Organomagnesium Anilides

The synthesis of ketones through addition of organometallic reagents to aliphatic carboxylic acids is a straightforward strategy that is limited to organolithium reagents. More desirable Grignard reagents can be activated and controlled with a bulky aniline‐derived turbo‐Hauser base. This operationally simple procedure allows the straightforward preparation of a variety of aliphatic and perfluoroalkyl ketones alike from functionalized alkyl, aryl and heteroaryl Grignard reagents.

Copper-Free Alternatives to Access Ketone Building Blocks from Grignard Reagents

Grignard reactions are an efficient way to form carbon-carbon bonds with widespread applications in large-scale processes. Classically, the electrophiles of choice to form ketones from Grignard reagents are acid chlorides. The reactions are typically catalyzed by additives such as CuCl to increase selectivity and yields. This work was focused on the use of acetic anhydride as an alternative to acetic chloride in the synthesis of 4-fluoro-2-(trifluoromethyl)acetophenone (3), a useful intermediate for the synthesis of active agricultural ingredients. The use of acetic anhydride as an electrophile not only equals but also surpasses acetic chloride in yield and selectivity, while also being more tolerable toward higher reaction temperatures. Furthermore, the reaction was performed in the absence of any additive, making it a highly attractive process for large-scale production. Computational mechanistic studies suggest that this advantageous behavior can be ascribed to the superior complexation of carboxylic acid anhydrides in the transition state.

Mechanochemical Grignard Reactions with Gaseous CO2 and Sodium Methyl Carbonate

A one-pot three-step protocol for the preparation of Grignard reagents from organobromides in a ball mill and their subsequent reactions with gaseous carbon dioxide (CO 2 ) or sodium methyl carbonate providing aryl and alkyl carboxylic acids in up to 82% yield is reported. Noteworthy are the short reaction times and the significantly reduced solvent amounts [2.0 equiv. for liquid assisted grinding (LAG) conditions]. Unexpectedly, aryl bromides with methoxy substituents lead to symmetric ketones as major products.

Deoxygenative Functionalizations of Aldehydes, Ketones and Carboxylic Acids

Conversion of carbonyl compounds, including aldehydes, ketones and carboxylic acids, into functionalized alkanes via deoxygenation would be highly desirable from a sustainability perspective and very enabling in chemical synthesis. This review covers the recent methodology development in carbonyl and carboxyl deoxygenative functionalizations, highlighting some typical and significant contributions in this field. These advances will be categorized based on types of bond formation, and in each part, selected examples will be discussed from their generalized mechanistic perspectives. Four summarized reactivity modes of aldehydes and ketones during the deoxygenation, namely, bis-electrophile, carbenoid, bis-nucleophile and alkyl radical, are presented, while the carboxylic acids are deoxygenated mainly via activated carbonyl or acetal intermediates.

Development of Trifluoromethanesulfonic Acid-Immobilized Nitrogen-Doped Carbon-Incarcerated Niobia Nanoparticle Catalysts for Friedel-Crafts Acylation

Heterogeneous trifluoromethanesulfonic acid-immobilized nitrogen-doped carbon-incarcerated niobia nanoparticle catalysts (NCI-Nb-TfOH) that show excellent catalytic performance with low niobium loading (1 mol %) in Friedel-Crafts acylation have been developed. These catalysts exhibit higher activity and higher tolerance to catalytic poisons compared with the previously reported TfOH-treated NCI-Ti catalysts, leading to a broader substrate scope. The catalysts were characterized via spectroscopic and microscopic studies.

Light-Driven Carbene Catalysis for the Synthesis of Aliphatic and α-Amino Ketones

Single-electron N-heterocyclic carbene (NHC) catalysis has gained attention recently for the synthesis of C-C bonds. Guided by density functional theory and mechanistic analyses, we report the light-driven synthesis of aliphatic and α-amino ketones using single-electron NHC operators. Computational and experimental results reveal that the reactivity of the key radical intermediate is substrate-dependent and can be modulated through steric and electronic parameters of the NHC. Catalyst potential is harnessed in the visible-light driven generation of an acyl azolium radical species that undergoes selective coupling with various radical partners to afford diverse ketone products. This methodology is showcased in the direct late-stage functionalization of amino acids and pharmaceutical compounds, highlighting the utility of single-electron NHC operators.

N-Hydroxyphthalimidyl diazoacetate (NHPI-DA): a modular methylene linchpin for the C-H alkylation of indoles

Despite the extensive studies on the reactions between conventional diazocompounds and indoles, these are still limited by the independent synthesis of the carbene precursors, the specific catalysts, and the required multi-step manipulation of the products. In this work, we explore redox-active carbenes in the expedited and divergent synthesis of functionalized indoles. NHPI-DA displays unusual efficiency and selectivity to yield insertion products that can be swiftly elaborated into boron and carbon substituents that are particularly problematic in carbene-mediated reactions.

Computational and Experimental Study of Turbo-Organomagnesium Amide Reagents: Cubane Aggregates as Reactive Intermediates in Pummerer Coupling

The dynamic equilibria of organomagnesium reagents are known to be very complex, and the relative reactivity of their components is poorly understood. Herein, a combination of DFT calculations and kinetic experiments is employed to investigate the detailed reaction mechanism of the Pummerer coupling between sulfoxides and turbo-organomagnesium amides. Among the various aggregates studied, unprecedented heterometallic open cubane structures are demonstrated to yield favorable barriers through a concerted anion-anion coupling/ S-O cleavage step. Beyond a structural curiosity, these results introduce open cubane organometallics as key reactive intermediates in turbo-organomagnesium amide mixtures.

A Fast and General Route to Ketones from Amides and Organolithium Compounds under Aerobic Conditions: Synthetic and Mechanistic Aspects

We report that the nucleophilic acyl substitution reaction of aliphatic and (hetero)aromatic amides by organolithium reagents proceeds quickly (20 s reaction time), efficiently, and chemoselectively with a broad substrate scope in the environmentally responsible cyclopentyl methyl ether, at ambient temperature and under air, to provide ketones in up to 93 % yield with an effective suppression of the notorious over-addition reaction. Detailed DFT calculations and NMR investigations support the experimental results. The described methodology was proven to be amenable to scale-up and recyclability protocols. Contrasting classical procedures carried out under inert atmospheres, this work lays the foundation for a profound paradigm shift of the reactivity of carboxylic acid amides with organolithiums, with ketones being straightforwardly obtained by simply combining the reagents under aerobic conditions and with no need of using previously modified or pre-activated amides, as recommended.

Decarboxylative Alkyl Coupling Promoted by NADH and Blue Light

Photoexcited dihydronicotinamides like NADH and analogues have been found to generate alkyl radicals upon reductive decarboxylation of redox-active esters without auxiliary photocatalysts. This principle allowed aliphatic photocoupling between redox-active carboxylate derivatives and electron-poor olefins, displaying surprising water and air-tolerance and unusually high coupling rates in dilute conditions. The orthogonality of the reaction in the presence of other carboxylic acids and its utility in the functionalization of DNA is presented, notably using visible light in combination with NADH, the ubiquitous reductant of life.

Mg3N2-assisted one-pot synthesis of 1,3-disubstituted imidazo[1,5-a]pyridine

A novel Mg₃N₂-assisted one-pot annulation strategy has been developed via cyclo-condensation reaction of 2-pyridyl ketones with alkyl glyoxylates or aldehydes, allowing the formation of imidazo[1,5-a]pyridines exclusively with an exellent yield.