Light-Driven Three-Component Carbonylation of Aryl Halides Using Abundant Metal Carbonyl

Carbonyl compounds are widely found in various pharmaceutical intermediates and synthetic precursors. Herein we report a simple light-driven three-component aryl halide process for synthesizing a variety of carbonylation products, utilizing Co2(CO)8 as an abundant solid carbonyl source, in good to excellent yields. The products can easily be subjected to further functionalization in synthesis. Mechanism studies indicated that this reaction is enabled by aryl radical generation and the subsequent CO insertion, alkene insertion, and protonation process.

Enantioselective Potassium-Catalyzed Wittig Olefinations

We report asymmetric potassium-isothiourea-boronate-catalyzed Wittig olefinations of 4-substituted cyclohexanones with non-stabilized phosphorus ylides to afford highly enantioenriched axially chiral alkenes. The optimal catalyst features an unusual macrocyclic amide-potassium-boronate chelate. Kinetic and spectroscopic analyses are consistent with a Lewis acid mechanism for the catalytic olefination that results in the formation of the oxaphosphetane adduct under cryogenic conditions. Thermal fragmentation of the oxaphosphetane to the alkene product occurs after the reaction is complete. Computational studies indicate that cycloaddition proceeds via a stepwise mechanism involving enantiodetermining polar 1,2-addition to afford an intermediate potassium betaine complex.

Reactivity and Stability of (Hetero)Benzylic Alkenes via the Wittig Olefination Reaction

Wittig olefination at hetero-benzylic positions for electron-deficient and electron-rich heterocycles has been studied. The electronic effects of some commonly used protective groups associated with the N-heterocycles were also investigated for alkenes obtained in the context of the widely employed Wittig olefination reaction. It was observed that hetero-benzylic positions of the pyridine, thiophene and furan derivatives were stable after Wittig olefination. Similarly, electron-withdrawing groups (EWGs) attached to N-heterocycles (indole and pyrrole derivatives) directly enhanced the stability of the benzylic position during and after Wittig olefination, resulting in the formation of stable alkenes. Conversely, electron-donating group (EDG)-associated N-heterocycles boosted the reactivity of benzylic alkene, leading to lower yields or decomposition of the olefination products.

A Triphenylphosphine-Based Microporous Polymer for a Wittig Reaction Cycle in the Solid State

The Wittig reaction is a key step in industrial processes to synthesise large quantities of vitamin A and various other important chemicals that are used in daily life. This article presents a pathway to achieve the Wittig reaction in a solid network. A highly porous triphenylphosphine-based polymer was applied as a solid Wittig reagent that undergoes, in a multi-step cycle, in total six post-synthetic modifications. This allowed for regeneration of the solid Wittig reagent and reuse for the same reaction cycle. Of particular industrial relevance is that the newly developed material also enables a simple way of separating the product by filtration. Therefore, additional costly and difficult separation and purification steps are no longer needed.

Wittig and Wittig-Horner Reactions under Sonication Conditions

Carbonyl olefinations are among the most important organic syntheses that form C=C bonds, as they usually have high yields and in addition offer excellent stereoselectivity. Due to these advantages, carbonyl olefinations have important pharmaceutical and industrial applications. These reactions contain an additional step of an α-functionalized carbanion to an aldehyde or ketone to produce alkenes, but syntheses performed using metal carbene complexes are also known. The Wittig reaction is an example of carbonyl olefination, one of the best ways to synthesize alkenes. This involves the chemical reaction between an aldehyde or ketone with a so-called Wittig reagent, for instance phosphonium ylide. Triphenylphosphine-derived ylides and trialkylphosphine-derived ylides are the most common phosphorous compounds used as Wittig reagents. The Wittig reaction is commonly involved in the synthesis of novel anti-cancer and anti-viral compounds. In recent decades, the use of ultrasound on the Wittig reaction (and on different modified Wittig syntheses, such as the Wittig-Horner reaction or the aza-Wittig method) has been studied as a green synthesis. In addition to the advantage of green synthesis, the use of ultrasounds in general also improved the yield and reduced the reaction time. All of these chemical syntheses conducted under ultrasound will be described further in the present review.

Recent Advances in Alkenyl sp2 C-H and C-F Bond Functionalizations: Scope, Mechanism, and Applications

Alkenes and their derivatives are featured widely in a variety of natural products, pharmaceuticals, and advanced materials. Significant efforts have been made toward the development of new and practical methods to access this important class of compounds by selectively activating the alkenyl C(sp²)-H bonds in recent years. In this comprehensive review, we describe the state-of-the-art strategies for the direct functionalization of alkenyl sp² C-H and C-F bonds until June 2022. Moreover, metal-free, photoredox, and electrochemical strategies are also covered. For clarity, this review has been divided into two parts; the first part focuses on currently available alkenyl sp² C-H functionalization methods using different alkene derivatives as the starting materials, and the second part describes the alkenyl sp² C-F bond functionalization using easily accessible gem-difluoroalkenes as the starting material. This review includes the scope, limitations, mechanistic studies, stereoselective control (using directing groups as well as metal-migration strategies), and their applications to complex molecule synthesis where appropriate. Overall, this comprehensive review aims to document the considerable advancements, current status, and emerging work by critically summarizing the contributions of researchers working in this fascinating area and is expected to stimulate novel, innovative, and broadly applicable strategies for alkenyl sp² C-H and C-F bond functionalizations in the coming years.

Structure and inhibition mechanism of some synthetic compounds and phenolic derivatives as tyrosinase inhibitors: review and new insight

Safety concerns are the primary consideration to identify and detection of enzyme inhibitors. In this regard, safe and potent tyrosinase inhibitors play important role in enhancing nutritional quality, health promotion and also prevent further damages. The present review focuses on the recent and efficient tyrosinase inhibitors discovered from both synthetic sources and synthesized phenolic compounds, including flavonoid, carvacrol, thymol, cinnamic acid and resorcinol derivatives. The inhibitory activity of these compounds was analyzed according to chemical structure, IC₅₀, K_i and their binding energy. Further, inhibition mechanism and the biological effects of some these inhibitors with potential application in food, agricultural, cosmetic and pharmaceutical industries were briefly discussed. Molecular docking procedure was performed on some derivatives and demonstrated favorable binding affinity with amino acid residues of mushroom tyrosinase (PDB ID: 2Y9X). The information offered showed that the substitution pattern of hydroxyl groups at the phenyl ring is an important factor of tyrosinase inhibitory activity. The results confirmed that understanding structural modification of inhibitors is a key role in finding novel and efficacious tyrosinase inhibitors.Communicated by Ramaswamy H. Sarma.

Rhodium-catalysed direct formylmethylation using vinylene carbonate and sequential dehydrogenative esterification

A rhodium-catalysed direct formylmethylation adopting vinylene carbonate as an ethynol equivalent is reported. The developed catalytic system is further utilised for the oxidant-free production of esters with the liberation of hydrogen gas. Some control experiments are conducted to elucidate the reaction mechanism.

One-Step Synthesis of Triphenylphosphonium Salts from (Het)arylmethyl Alcohols

Two approaches for the synthesis of substituted phosphonium salts from easily available benzyl alcohols and their heterocyclic analogs have been developed. The developed protocols are complementary: the direct mixing of alcohol, trimethylsilyl bromide, and triphenylphosphine in 1,4-dioxane followed by heating at 80 °C was found to be more efficient for acid-sensitive substrates, such as salicyl or furfuryl alcohols as well as secondary benzyl alcohols, while a one-pot procedure including sequential addition of trimethylsilyl bromide and triphenylphosphine gave higher yields for benzyl alcohols bearing electroneutral or electron-withdrawing substituents.

Unusual Application for Phosphonium Salts and Phosphoranes: Synthesis of Chalcogenides

A novel strategy for the synthesis of sulfides and selenides from phosphonium salts and thio- or selenesulfonates, commercially available compounds, is described. When phosphoranes were used in the reaction, different products were obtained. The methodology does not require the use of metals, reactive species, or anhydrous conditions to be performed.

Construction of indeno[1,2-b]pyrroles via chemoselective N-acylation/cyclization/Wittig reaction sequence

An efficient protocol for the chemoselective construction of the indeno[1,2-b]pyrroles and rearranged indeno[1,2-b]pyrrole derivatives is reported via an N-acylation/cyclization/Wittig reaction. Extensive mechanistic investigations revealed that the initially formed crucial spiro-indene-1,2'-[1,3,4]oxadiazol intermediate further reacts with phosphine to generate betaine, thus predominately resulting in the aforementioned heteroarenes proceeding by a Wittig reaction.

The wavelength-regulated stereodivergent synthesis of (Z)- and (E)-1,4-enediones from phosphonium ylides

The wavelength-regulated, photoredox-catalyzed stereodivergent synthesis of (Z)- and (E)-1,4-enediones from phosphonium ylides is reported.

One-Pot, Tandem Wittig Hydrogenation: Formal C(sp3)-C(sp3) Bond Formation with Extensive Scope

A one-pot, tandem Wittig hydrogenation of aldehydes with stabilized ylides is reported, representing a formal C(sp³)-C(sp³) bond construction. The tandem reaction operates under mild conditions, is high yielding, and is broad in scope. Chemoselectivity for olefin reduction is observed, and the methodology is demonstrated in the synthesis of lapatinib analogues and a formal synthesis of (±)-cuspareine. Early insights suggest that the chemoselectivity observed in the reduction step is due to partial poisoning of the catalyst, after step one, thus adding to the power of the one-pot procedure.

Diversity-Oriented Synthesis of Spiropentadiene Pyrazolones and 1H-Oxepino[2,3-c]pyrazoles from Doubly Conjugated Pyrazolones via Intramolecular Wittig Reaction

An efficient method for the diversity-oriented synthesis of spiropentadiene pyrazolones and 1H-oxepino[2,3-c]pyrazoles is reported. The methodology attributes O-acylation of phosphorus zwitterions which were formed by a tandem phospha-1,6-addition of PBu₃ to α,β,γ,δ-unsaturated pyrazolones, further generating betaine intermediates that preferentially resulted in the aforementioned cyclic products in a diversity-oriented manner. The mechanistic investigations revealed that formation of the betaines is the key step to provide the products via an intramolecular Wittig reaction or an unprecedented δ-C-acylation/cyclization/Wittig reaction.

Post-Polymerization Modification of Ring Opening Metathesis Polymerization (ROMP)-Derived Materials Using Wittig Reactions

This communication describes our recent efforts to utilize Wittig olefination reactions for the post-polymerization modification of polynorbornene derivatives prepared through ring opening metathesis polymerization (ROMP). Polymerizing α-bromo ester-containing norbornenes provides polymers that can undergo facile substitution with triphenylphosphine. The resulting polymeric phosphonium salt is then deprotonated to form an ylide that undergoes reaction with various aryl aldehydes in a one-pot fashion to yield the respective cinnamates. These materials can undergo further modification through photo-induced [2 + 2] cycloaddition cross-linking reactions.

Silver catalyzed proto- and sila-Nakamura-type α-vinylation of silyl enol ethers with dichloroacetylene. Divergent formation of stereochemically pure tri- and tetrasubstituted olefins

The silver-catalyzed reaction of silyl enol ethers with dichloroacetylene (DCA) is described. When DCA was used as a solution in diethyl ether, we found that the silyl group was transferred to the vinyl group, resulting in stereochemically pure tetrasubstituted olefins. However, when DCA was used as a solution in the more polar acetonitrile, protonation was the major pathway, and trisubstituted olefins were the dominant products.

Recent advances in the annulation of Morita–Baylis–Hillman adducts

In this review, we summarize some of the most recent advances in the construction of cyclic compounds from the annulation of Morita–Baylis–Hillman (MBH) adducts, which have demonstrated their importance by possessing diverse functional groups.