Sensitive Functional Groups Research Articles

Ylide‐Functionalized Diisopropyl Phosphine (prYPhos): A Ligand for Selective Suzuki‐Miyaura Couplings of Aryl Chlorides

AbstractThe ylide‐functionalized diisopropyl phosphine (prYPhos) promotes Pd‐catalyzed Suzuki‐Miyaura couplings of aryl chlorides and bromides with arylboronic acids. Using Pd2(dba)3/prYPhos as the catalyst and K2CO3 as the base, various (hetero)biaryls were synthesized in 45–98% yields at mild reaction conditions, tolerating sensitive functional groups and steric hindrance. The electron rich, sterically demanding ligand induces a high selectivity for halides versus triflate. Chloroaryl triflates were selectively coupled at the chloride, leaving inherently more reactive triflate groups in place.magnified image

A cationic iridium(III) complex containing a thiosemicarbazide unit: Synthesis and application for turn-on chemiluminescent detection of Hg2+

A novel cationic iridium(III) complex [(ppy)2Ir(bPCPC)]PF6 (ppy: 2-phenylpyridine; bPCPC: 2-([2,2′-bipyridine]-4-carbonyl)-N-phenylhydrazinecarbothioamide) containing a thiosemicarbazide unit was designed and synthesized. The thiosemicarbazide unit was a sensitive functional group to Hg2+, when it reacted with Hg2+, it was desulphurized and thus led to the formation of 1,3,4-oxadiazole, [(ppy)2Ir(bPCPC)]PF6 resultantly was used as a “turn-on” chemodosimeter for luminescent detection of Hg2+ in DMF/PBS buffer solution at pH = 7–11. Except for Ag+, recognition capability of [(ppy)2Ir(bPCPC)]PF6 to Hg2+ was not interfered by other common metal ions (Co2+, Li+, Zn2+, Pb2+, K+, Al3+, Na+, Mn2+, Cu2+, Fe2+, Fe3+, Cr3+, Ba2+, Mg2+, Ni2+ and Ca2+). The detection limit was 1.83 × 10−9 mol∙L−1 (0.37 ppb), which indicated the complex was a highly sensitive chemiluminescent detection reagent of Hg2+.

Iridium-Catalyzed Direct Reductive Amination of Ketones and Secondary Amines: Breaking the Aliphatic Wall.

Direct reductive amination (DRA) is a ubiquitous reaction in organic chemistry. This transformation between a carbonyl group and an amine is most often achieved by using a super stoichiometric amount of hazardous hydride reagents, thus being incompatible with many sensitive functional groups. DRA could also be achieved by means of chemo- or biocatalysis, thereby attracting the interest of industry as well as academic laboratories due to the virtually perfect atom economy. Although DRAs are well-established for substrate pairs such as aldehydes with either 1° or 2° amines as well as ketones with 1° amines, the current methodologies are limited in the case of ketones with 2° amines. Herein, we present a general DRA protocol that overcomes this major limitation by means of iridium catalysis. The applicability of the methodology is demonstrated by accessing an unprecedented range of biologically relevant tertiary amines starting from both aliphatic ketones and aliphatic amines. The choice of a disphosphane ligand (Josiphos A or Xantphos) is essential for the success of the transformation.

Difluoromethylarylation of Alkynes from [Bis(difluoroacetoxy)iodo]benzene: Access to CF2H-Containing Dibenzazepines.

A photoinduced radical difluoromethylarylation via tandem addition-cyclization of alkynes with easily available [bis(difluoroacetoxy)iodo]benzene is accomplished, providing a straightforward and practical route for the construction of difluoromethylated dibenzazepines. Various sensitive functional groups can be compatible under photoinduced conditions. Mechanism investigation reveals that this transformation is initiated by the addition of alkyne with difluoromethyl radical, generated in situ from [bis(difluoroacetoxy)iodo]benzene.

Acceptorless dehydrogenation of primary alcohols to carboxylic acids by self-supported NHC-Ru single-site catalysts

The acceptorless dehydrogenation of diverse aromatic and aliphatic primary alcohols to corresponding carboxylic acids has been accomplished by self-supported NHC-Ru single-site catalysts under mild reaction conditions. Besides broad substrates with excellent activity, selectivity and good tolerance to sensitive functional groups, the solid single-site catalyst could be recovered and reused for more than 20 runs without deactivation. Remarkably, up to 1.8 × 104 turnover numbers could be achieved by this newly developed sustainable protocol in gram scale at low catalyst loading, highlighting its potential in industry.

Palladium‐Catalyzed Tail‐to‐Tail Reductive Dimerization of Terminal Alkynes to 2,3‐Dibranched Butadienes

AbstractThe palladium‐catalyzed tail‐to‐tail reductive dimerization of terminal alkynes is described for the first time. Aromatic terminal alkynes bearing diverse and sensitive functional groups as well as aliphatic terminal alkynes are efficiently transformed to 2,3‐dibranched butadienes. The key to achieve a selective tail‐to‐tail reductive dimerization reaction is to control appropriately the acidity of the reaction solution, which is accomplished by a combined use of pivalic acid and para‐toluenesulfonic acid. The tail‐to‐tail reductive dimerization reaction is proposed to proceed via a cationic alkenyl palladium intermediate under acidic conditions.

Palladium-Catalyzed Tail-to-Tail Reductive Dimerization of Terminal Alkynes to 2,3-Dibranched Butadienes.

The palladium-catalyzed tail-to-tail reductive dimerization of terminal alkynes is described for the first time. Aromatic terminal alkynes bearing diverse and sensitive functional groups as well as aliphatic terminal alkynes are efficiently transformed to 2,3-dibranched butadienes. The key to achieve a selective tail-to-tail reductive dimerization reaction is to control appropriately the acidity of the reaction solution, which is accomplished by a combined use of pivalic acid and para-toluenesulfonic acid. The tail-to-tail reductive dimerization reaction is proposed to proceed via a cationic alkenyl palladium intermediate under acidic conditions.

C2-Selective, Functional-Group-Divergent Amination of Pyrimidines by Enthalpy-Controlled Nucleophilic Functionalization.

Synthesis of heteroaryl amines has been an important topic in organic chemistry because of their importance in small-molecule discovery. In particular, 2-aminopyrimidines represent a highly privileged structural motif that is prevalent in bioactive molecules, but a general strategy to introduce the pyrimidine C2-N bonds via direct functionalization is elusive. Here we describe a synthetic platform for site-selective C-H functionalization that affords pyrimidinyl iminium salt intermediates, which then can be transformed into various amine products in situ. Mechanism-based reagent design allowed for the C2-selective amination of pyrimidines, opening the new scope of site-selective heteroaryl C-H functionalization. Our method is compatible with a broad range of pyrimidines with sensitive functional groups and can access complex aminopyrimidines with high selectivity.

Facile synthesis of N-doped graphene encapsulated Ni@N/C catalyst and its catalysis for highly selective semi-hydrogenation of alkynes

Although precious transition metals such as palladium, platinum, and iridium are widely used in hydrogenation reactions, the earth-abundant transition metal-catalyzed highly selective semi-hydrogenation of terminal alkynes to terminal alkenes remains poorly developed and a challenge. Herein we demonstrate the excellent selective, cost-effective semi-hydrogenation of terminal alkynes via a novel graphene encapsulated Ni@N/C catalyst. The graphene layer encapsulated nano-catalyst Ni@N/C could significantly avoid metal leaching and improve the stability of the catalyst. The strong interaction of nitrogen with the Ni nanoparticles regulates the activity of Ni towards selective semi-hydrogenation of terminal alkynes. Substrates having un-functionalized as well as functionalized substituents, and substrates having sensitive functional groups (olefins, ketones) which pose a challenge to hydrogenate, were semi-hydrogenated with excellent conversion (up to 99%) and selectivity (up to 99%) under optimized reaction conditions.

Metal-Free, Rapid, and Highly Chemoselective Reduction of Aromatic Nitro Compounds at Room Temperature.

In this study, we developed a metal-free and highly chemoselective method for the reduction of aromatic nitro compounds. This reduction was performed using tetrahydroxydiboron [B2(OH)4] as the reductant and 4,4'-bipyridine as the organocatalyst and could be completed within 5 min at room temperature. Under optimal conditions, nitroarenes with sensitive functional groups, such as vinyl, ethynyl, carbonyl, and halogen, were converted into the corresponding anilines with excellent selectivity while avoiding the undesirable reduction of the sensitive functional groups.

Divergent cyanoalkylation/cyanoalkylsulfonylation of enamides under organophotoredox catalytic conditions.

An organophotoredox-catalyzed divergent cyanoalkylation/cyanoalkylsulfonylation of enamides in a highly regio- and stereoselective manner has been reported. In this mild and efficient protocol, cyclobutanone oxime esters serve as a cyanoalkylating source and inexpensive K2S2O5 serves as an SO2 surrogate. Broad substrate scope, compatibility of various sensitive functional groups and further functional group transformation are the highlights of this method.

Sustainable and fast synthesis of functionalized quinoxalines promoted by natural deep eutectic solvents (NADESs)

A NADES, choline chloride/water, allows a high yielding preparation of pure quinoxalines embedding acid sensitive and other functional groups at room temperature in a very short reaction time.

Scalable selective electrochemical oxidation of sulfides to sulfoxides

An electrochemical protocol for the selective oxidation of sulfides to sulfoxides has been developed in which NaCl plays a dual role: (1) as an electrolyte for the electrochemical transformations and (2) as a redox mediator to avoid oxidation of sensitive functional groups.

Analysing ecological carrying capacity of bivalve aquaculture within the Yellow River Estuary ecoregion through mass-balance modelling

As the largest aquaculture producer in the world, China is facing the challenge of maintaining sustainability while continuing to develop the aquaculture industry to meet socio-economic needs. Models of trophic structure and energy flow can be used to analyse ecological carrying capacity in order to determine whether a large and rapidly increasing aquaculture industry potentially puts sustainable development at risk. The Yellow River Estuary ecoregion in Shandong Province, China, is an ecologically important region, with extensive bivalve aquaculture that is increasing rapidly at an overall growth rate of 4% annually during recent decades. A trophic mass-balance model was used to analyse the ecological carrying capacity of bivalve aquaculture in this ecoregion. The biomass of cultured bivalves is currently 13.3 t km-2 and could be increased to 62.0 t km-2 without exceeding the ecological carrying capacity. Zooplankton are a key factor limiting the ecological carrying capacity and represent a sensitive functional group within the food web system in this ecoregion. At the ecological carrying capacity of cultured bivalves in the Yellow River Estuary ecoregion, harvests would amount to 353.2 t km-2 yr-1 or a total of 4.2 million t yr-1 in this region. If the current average rate of growth in aquaculture in China is maintained, under cautious development, the biomass of cultured bivalves would reach half of the estimated ecological carrying capacity (31.0 t km-2) after 20 yr. This implies that there is capacity for sustainable development of bivalve aquaculture under current environmental conditions.

Photomediated reductive coupling of nitroarenes with aldehydes for amide synthesis.

In view of the widespread significance of amide functional groups in organic synthesis and pharmaceutical studies, an efficient and practical synthetic protocol that avoids the use of stoichiometric activating reagents or metallic reductants is highly desirable. A straight-forward pathway to access amides from abundant chemical feedstock would offer a strategic advantage in the synthesis of complex amides. We herein disclose a direct reductive amidation reaction using readily available aldehydes and nitroarenes enabled by photo-mediated hydrogen atom transfer catalysis. It avoids the use of metallic reductants and production of toxic chemical waste. While aldehydes represent a classic class of electrophilic synthons, the corresponding nucleophilic acyl radicals could be directly accessed by photo hydrogen atom transfer catalysis, enabling polarity inversion. Our method provides an orthogonal strategy to conventional amide couplings, tolerating nucleophilic substituents such as free alcohols and sensitive functional groups to amines such as carbonyl or formyl groups. The synthetic utilization of this reductive amidation is demonstrated by the late-stage modification of complex biologically active molecules and direct access of drug molecules leflunomide and lidocaine.

Photochemical C-H arylation of heteroarenes for DNA-encoded library synthesis.

DNA-encoded library (DEL) technology has emerged as a time- and cost-efficient technique for the identification of therapeutic candidates in the pharmaceutical industry. Although several reaction classes have been successfully validated in DEL environments, there remains a paucity of DNA-compatible reactions that harness building blocks (BBs) from readily available substructures bearing multifunctional handles for further library diversification under mild, dilute, and aqueous conditions. In this study, the direct C–H carbofunctionalization of medicinally-relevant heteroarenes can be accomplished via the photoreduction of DNA-conjugated (hetero)aryl halides to deliver reactive aryl radical intermediates in a regulated fashion within minutes of blue light illumination. A broad array of electron-rich and electron-poor heteroarene scaffolds undergo transformation in the presence of sensitive functional groups.

Synthesis of 3-Aryl-ortho-carboranes with Sensitive Functional Groups.

A simple and efficient method was developed for the one-pot synthesis of 3-aryl derivatives of ortho-carborane with sensitive functional groups using 3-iodo-ortho-carborane and aryl zinc bromides that were generated in situ. A series of 3-aryl-ortho-carboranes, including those containing nitrile and ester groups, 3-RC6H4-1,2-C2B10H11 (R = p-Me, p-NMe2, p-OCH2OMe, p-OMe, o-CN, p-CN, o-COOEt, m-COOEt, p-COOEt) was synthesized using this approach. The solid-state structures of 3-RC6H4-1,2-C2B10H11 (R = p-OMe, o-CN, and p-CN) were determined by single crystal X-ray diffraction. The intramolecular hydrogen bonding involving the ortho-substituents of the aryl ring and the CH and BH groups of carborane was discussed.

In-situ facile synthesis novel N-doped thin graphene layer encapsulated Pd@N/C catalyst for semi-hydrogenation of alkynes

Transition metal-catalyzed semi-hydrogenation of alkynes has become one of the most popular methods for alkene synthesis. Specifically, the noble metal Pd, Rh, and Ru-based heterogeneous catalysts have been widely studied and utilized in both academia and industry. But the supported noble metal catalysts are generally suffering from leaching or aggregation during harsh reaction conditions, which resulting low catalytic reactivity and stability. Herein, we reported the facile synthesis of nitrogen doped graphene encapsulated Pd catalyst and its application in the chemo-selective semi-hydrogenation of alkynes. The graphene layer served as “bulletproof” over the active Pd Nano metal species, which was confirmed by X-ray and TEM analysis, enhanced the catalytic stability during the reaction conditions. The optimized prepared Pd@N/C catalyst showed excellent efficiency in semi-hydrogenation of phenylacetylene and other types of alkynes with un-functionalized or functionalized substituents, including the hydrogenation sensitive functional groups (NO2, ester, and halogen).

A Short Total Synthesis of Benzophenanthridine Alkaloids via a Rhodium(III)-Catalyzed C-H Ring-Opening Reaction.

The biologically important naturally available benzophenanthridines were prepared efficiently in three steps with overall good yields. A new synthetic methodology involving a rhodium(III) catalyzed redox-neutral ring-opening of 7-azabenzonorbornadienes with aromatic aldoximes is developed to synthesize the target molecules. The developed C-H ring-opening reaction is highly diastereoselective and compatible with various sensitive functional group substituted aromatic aldoximes as well as substituted 7-azabenzonorbornadienes. The ring-opening products were transformed into highly sensitive 13,14-dehydrobenzo phenanthridine derivatives by HCl hydrolysis. Subsequently, 13,14-dehydrobenzophenanthridines were converted into biologically important benzophenanthridine alkaloids in the presence of DDQ. A possible reaction mechanism was proposed for the C-H ring-opening reaction and supported by the deuterium labeling studies.

Development and Mechanistic Studies of the Iridium-Catalyzed C-H Alkenylation of Enamides with Vinyl Acetates: A Versatile Approach for Ketone Functionalization.

Ketone functionalization is a cornerstone of organic synthesis. Herein, we describe the development of an intermolecular C-H alkenylation of enamides with the feedstock chemical vinyl acetate to access diverse functionalized ketones. Enamides derived from various cyclic and acyclic ketones reacted efficiently, and a number of sensitive functional groups were tolerated. In this iridium-catalyzed transformation, two structurally and electronically similar alkenes-enamide and vinyl acetate-underwent selective cross-coupling through C-H activation. No reaction partner was used in large excess. The reaction is also pH- and redox-neutral with HOAc as the only stoichiometric by-product. Detailed experimental and computational studies revealed a reaction mechanism involving 1,2-Ir-C migratory insertion followed by syn-β-acetoxy elimination, which is different from that of previous vinyl acetate mediated C-H activation reactions. Finally, the alkenylation product can serve as a versatile intermediate to deliver a variety of structurally modified ketones.