B(C 6 F 5 ) 3 ‐Catalyzed Hydroarylation of Terminal Alkynes with Phenols

A selective photoinduced radical O-alkenylation of phenols and naphthols with terminal alkynes

The visible light-promoted O-alkenylation of phenols and naphthols with terminal alkynes is achieved using 2,4,6-tris(4-fluorophenyl)pyrylium tetrafluoroborate (T(p-F)PPT) as a photocatalyst at room temperature without the need of any external ligand or additive. Apart from its excellent functional group tolerance, the protocol described herein represents an appealing alternative strategy to classical transition-metal catalysed hydroarylation reactions. Mechanistic investigations revealed that the reaction involves a radical pathway. The utility of the hydroarylated products for the synthesis of fused benzofurans via a one-pot annulation was also demonstrated. Herein, we report the first intermolecular radical hydroarylation of alkynes.

Csp2-H functionalization of phenols: an effective access route to valuable materials via Csp2-C bond formation

In the vast majority of top-selling pharmaceutical and industrial products, phenolic structural motifs are highly prevalent. Non-functionalized simple phenols serve as building blocks in the synthesis of value-added chemicals. It is worth mentioning that lignin, being the largest renewable biomass source of aromatic building blocks in nature, mainly consists of phenolic units, which enable the production of structurally diverse phenols. Given their remarkable applicability in the chemical value chain, many efforts have been devoted to increasing the molecular complexity of the phenolic scaffold. Among the key techniques, direct functionalization of Csp2-H is a powerful tool, enabling the construction of new Csp2-C bonds in an economical and atomic manner. Herein we present and summarize the large plethora of direct Csp2-H functionalization methods that enables scaffold diversification of simple, unprotected phenols, leading to the formation of new Csp2-C bonds. In this review article, we intend to summarize the contributions that appeared in the literature mainly in the last 5 years dealing with the functionalization of unprotected phenols, both catalytic and non-catalytic. Our goal is to highlight the key findings and the ongoing challenges in the stimulating and growing research dedicated to the development of new protocols for the valorization of phenols.

H2 O ⋅ B(C6 F5 )3 -Catalyzed para-Alkylation of Anilines with Alkenes Applied to Late-Stage Functionalization of Non-Steroidal Anti-Inflammatory Drugs

Anilines are core motifs in a variety of important molecules including medicines, materials and agrochemicals. We report a straightforward procedure that allows access to new chemical space of anilines via their para-C-H alkylation. The method utilizes commercially available catalytic H2 O ⋅ B(C6 F5 )3 and is highly selective for para-C-alkylation (over N-alkylation and ortho-C-alkylation) of anilines, with a wide scope in both the aniline substrates and alkene coupling partners. Readily available alkenes are used, and include new classes of alkene for the first time. The mild reaction conditions have allowed the procedure to be applied to the late-stage-functionalization of non-steroidal anti-inflammatory drugs (NSAIDs), including fenamic acids and diclofenac. The formed novel NSAID derivatives display improved anti-inflammatory properties over the parent NSAID structure.

Atom-economic and stereoselective catalytic synthesis of fully substituted enol esters/carbonates of amides in acyclic systems enabled by boron Lewis acid catalysis

Carboacyloxylation of internal alkynes is emerging as a powerful and straightforward strategy for enol ester synthesis. However, the reported examples come with limitations, including the utilization of noble metal catalysts, the control of regio- and Z/E selectivity, and an application in the synthesis of enol carbonates. Herein, a boron Lewis acid-catalyzed intermolecular carboacyloxylation of ynamides with esters to access fully substituted acyclic enol esters in high yield with generally high Z/E selectivity (up to >96 : 4) is reported. Most importantly, readily available allylic carbonates are also compatible with this difunctionalization reaction, representing an atom-economic, catalytic and stereoselective protocol for the construction of acyclic β,β-disubstituted enol carbonates of amides for the first time. The application of the carboacyloxylation products to decarboxylative allylations provided a ready access to enantioenriched α-quaternary amides. Moreover, experimental studies and theoretical calculations were performed to illustrate the reaction mechanism and rationalize the stereochemistry.

Recent Advances in Regioselective C-H Bond Functionalization of Free Phenols

Phenols are important readily available synthetic building blocks and starting materials for organic synthetic transformations, which are widely found in agrochemicals, pharmaceuticals, and functional materials. The C-H functionalization of free phenols has proven to be an extremely useful tool in organic synthesis, which provides efficient increases in phenol molecular complexity. Therefore, approaches to functionalizing existing C-H bonds of free phenols have continuously attracted the attention of organic chemists. In this review, we summarize the current knowledge and recent advances in ortho-, meta-, and para-selective C-H functionalization of free phenols in the last five years.

Lewis Acid-Catalyzed Remote Site-Selective Ring Deconstruction of Cyclobuteno[a]naphthalene-4-ones to Access Unsymmetric 1,1-Diarylated Olefins

A catalytic site-selective ring deconstruction of cyclobuteno[a]naphthalene-4-ones with alcohols is reported, enabling the direct production of a wide range of unsymmetric 1,1-diarylated olefins with good yields and complete regioselectivity. The late-stage application of these resulting terminal olefins demonstrates great possibilities to apply this strategy to complex molecules. The protocol features good functional group compatibility, broad substrate scope, and controllable site selectivity.

Boron Lewis Acid Catalyzed Intermolecular trans-Hydroarylation of Ynamides with Hydroxyarenes

An atom-economic protocol for the efficient and highly chemo- and stereoselective trans-hydroarylation of ynamides with hydroxyarenes catalyzed by B(C₆F₅)₃ has been developed. Use of readily available starting materials, low catalyst loading, mild reaction conditions, a broad substrate scope, ease of scale-up, and versatile functionalizations of the enamide products make this approach very practical and attractive.

Hydroboration reactions using transition metal borane and borate complexes: an overview

In recent years, the chemistry of transition metal borane and borate complexes has advanced fast with reasonable growth. Frequent utilisation of these complexes in hydrofunctionalisation reactions is one of the key driving forces for their development. As a result, the important role of borate complexes in the hydroboration/hydrosilylation/hydroamination of unsaturated organic species has been successfully demonstrated together with the isolation of many different boron-containing transition metal complexes such as borataallyl, vinylborane, silyl complexes featuring the known bonding modes of boron. Both the uncatalysed and catalysed hydroboration reactions using the transition metal borane/borate complexes are known, which show these complexes' huge potential. Careful investigation and fine-tuning of the electronic and steric properties of the borane/borate ligands has facilitated the synthesis of these transition metal complexes which are convenient for use in the hydroboration reactions. Furthermore, the systematic development of this field has established the connection between the structure and reactivity of these complexes and their utilisation in hydroboration reactions. This Frontier sheds light on the recent developments that have been made with hydroboration reactions using transition metal borane/borate complexes. Also, in this Frontier we have provided meaningful synthetic methods to make new boron-containing transition metal complexes together with mechanistic insights for some of these reactions.