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Herein, we describe a DABCO-catalyzed [4 + 2] annulation between 5-methylenehex-2-ynedioates and electron-deficient olefins to afford functionalized cyclohexadienes in good yields under mild conditions. The use of β- and ε-carbons of the substrates for C-C bond formation is distinct from previous reports showing a substrate-controlled divergent reactivity. The annulation is believed to proceed in domino cyclization initiated by a cross Rauhut-Currier reaction.

As the changes of biomarkers directly reflect the occurrence of degenerative diseases, accurate detection of biomarkers is of great significance for disease diagnosis and control. However, single index detection has high uncertainties to accurately reflect the pathological characteristics because of the complexity of the human internal environment and the extremely trace concentration of indicators. To this end, a method for simultaneous detection of dual-biomarkers based on anti-interference magnetic molecularly imprinted polymers (D-mag-MIPs) is thereby proposed, and successfully applied in human urine analysis for the detection of Parkinson's disease bio-indicators 4-dihydroxyphenylacetic acid (DOPAC) and dopamine (DA). In this work, carboxyl functionalized ferric oxide served as a magnetic core, laying a solid foundation for batch detection. Hyperbranched polyethylenimine, whose abundant amino groups can provide multiple interaction forces to templates with high affinity, is employed as a functional monomer. Relative to single-template MIPs, D-mag-MIPs achieve the detection of dual bio-indicators in a one-time test, reducing the false positive result probability and enhancing the detection accuracy. The proposed methodology has been evaluated to exhibit good anti-interference, satisfactory precision, low detection limits, wide linear ranges and fast batch detection for DA and DOPAC. This work thus offers an alternative and efficient pathway for convenient batch detection of dual bio-indicators from biofluids at once.

A highly efficient cascade cyclization of phenidones and enynones has been developed via a Ru(II)-catalyzed C-H activation initiated indole formation/Diels-Alder reaction/iminium ion cyclization sequence, which afforded hexacyclic indolines as single diastereomer in good to excellent yields with a broad substrate scope under mild conditions. The reaction features the simultaneous generation of five new chemical bonds and four new rings in one pot, providing a rapid and concise approach toward polycyclic indoline alkaloids and their analogues.

Herein we describe a phosphine-catalyzed internal redox [4 + 2] annulation of 1,4-enynoates with electron-deficient alkenes, in which the γ- and φ-C(sp3)-H of the enynoates are formally oxidized for the annulation while the alkynyl moiety is converted to an alkene. The reaction offers an efficient synthesis of highly functionalized cyclohexenes in moderate to good yields with exclusive regioselectivity and high diastereoselectivity under mild conditions.

We herein report a phosphine-catalyzed (3 + 2) annulation of cyclopropenones with a wide variety of electrophilic π systems, including aldehydes, ketoesters, imines, isocyanates, and carbodiimides, offering products of butenolides, butyrolactams, maleimides, and iminomaleimides, respectively, in high yields with broad substrate scope. An α-ketenyl phosphorous ylide is validated as the key intermediate, which undergoes preferential catalytic cyclization with aldehydes rather than stoichiometric Wittig olefinations. This phosphine-catalyzed activation of cyclopropenones thus supplies a versatile C3 synthon for formal cycloadditon reactions.

How to control the stability of oil-in-water (O/W) emulsions is one of the main topics for scientists working in colloidal systems. Recently, carbon dots (CDs) have received great interest as smart materials because of their excellent physicochemical properties and versatile applications. Herein, for the first time, advanced and switchable O/W emulsions are presented that are stabilized by the synergistic effect of cationic surfactant cetyltrimethylammonium bromide CTAB (emulsifier) and similarly charged CDs (stabilizer). In the formulated emulsion, the cationic surfactant molecules are adsorbed at the oil and water interface to decrease the interfacial tension and enrich the drops with a positive charge to ensure intensive electrostatic repulsions among them. On the contrary, cationic CDs are distributed in the water phase among the droplets to reduce the water secretion and prevent flocculation and droplet coalescence. The stabilizing effect is found to be universal for emulsions of a range of oil phases. Furthermore, the formulated emulsion is found to be switchable between "stable" and "unstable" modes by adding an equivalent of anionic surfactant sodium dodecyl benzene sulphonate (SDBS). The stabilized and switchable O/W emulsions are believed to have wide practical applications in water purification, pharmaceuticals, protein recognition, as well as catalysis.

A rhodium-catalyzed diastereoselective formal [5 + 2] annulation of indoles with cyclohexadienone-containing 1,6-enynes has been established via indole 2,3-difunctionalization. The reaction, probably proceeding through tandem indole C2-H alkenylation and intramolecular Friedel-Crafts alkylation relay, provides rapid construction of indole-fused oxepines in good to excellent yields with a broad substrate scope. This method also features concomitant construction of cis-hydrobenzo[b] oxepine scaffolds, a core unit found in numerous natural products of important biological activities.

We herein report a phosphine-catalyzed (3 + 2) annulation of cyclopropenones with a wide variety of electrophilic π systems, including aldehydes, ketoesters, imines, isocyanates, and carbodiimides, offering products of butenolides, butyrolactams, maleimides, and iminomaleimides, respectively, in high yields with broad substrate scope. An α-ketenyl phosphorous ylide is validated as the key intermediate, which undergoes preferential catalytic cyclization with aldehydes rather than stoichiometric Wittig olefinations. This phosphine-catalyzed activation of cyclopropenones thus supplies a versatile C

An efficient Cp*RhIII-catalyzed formal C(sp3)–H activation/spiroannulation of alkylidene Meldrum’s acids with alkynes has been developed using catalytical Cu(OAc)2 and air as the oxidant. This reac...

An efficient regioselective and stereoselective cascade annulation of indoles with alkynediones has been demonstrated via a Cp*RhIII-catalyzed indole C2–H activation by using N-carboamide directing groups in good to excellent yields with a broad substrate scope, which further realized the C2 and C3 difunctionalization of indoles in one-pot. This methodology simultaneously provides a novel and straightforward approach to free (NH) tetrahydrocarbazoles with continuous quaternary carbons and pyridoindolones, which are valuable intermediates in total synthesis of the related indole alkaloids.

Strongly hydrogen-bonded compounds such as 1,3,5-triamino-2,4,6‑trinitrobenzene (TATB, an important insensitive high explosive) have excellent stability, but poor solubilities to limit their recrystallization, purification and recycling. In this study, core-shell clusters based on symmetrical tetra-n-alkylammonium [TTA]

A highly efficient Ru(II)-catalyzed regio- and stereospecific hydro-oxycarbonylation of unsymmetrical internal alkynes bearing a difunctional 2-pyridyloxy directing group with carboxylic acids has been developed, which provides allylic (

The reactivity of allylic phosphorus ylides generated in situ from alkoxycarbonylmethylenephosphoranes and propiolates is investigated toward isocyanates and aromatic aldehydes, which leads to one-pot multicomponent benzannulations for efficient synthesis of polysubstituted anilines and biaryls, respectively. The mechanism may involve a tandem [2+2] cycloaddition/fragmentation/Wittig/cyclization/elimination/aromatization sequence.

Cyclopropane is one of the most reactive functionalities owing to its intrinsic ring strain. Transition-metal catalysis and Lewis acid catalysis have been extensively used in ring openings of cyclopropanes; however, Lewis base-catalyzed activation of cyclopropanes remains largely unexplored. Upon nucleophilic attack with Lewis bases, cyclopropanes undergo ring cleavage in a manner known as homoconjugate addition to form zwitterionic intermediates, which have significant potential for reaction development but have garnered little attention. Here, we present a brief overview of this area, with an emphasis on our recent efforts on Lewis base-catalyzed rearrangement reactions of electron-deficient cyclopropanes using the homoconjugate addition process.1 Introduction2 DABCO-Catalyzed Cloke–Wilson Rearrangement of Cyclopropyl Ketones3 Hydroxylamine-Mediated Tandem Cloke–Wilson/Boulton–­Katritzky Reaction of Cyclopropyl Ketones4 Phosphine-Catalyzed Rearrangement of Vinylcyclopropyl Ketones To Form Cycloheptenones5 Phosphine-Catalyzed Rearrangement of Alkylidenecyclopropyl Ketones To Form Polysubstituted Furans and Dienones6 Conclusion and Outlook

We report a phosphine-catalyzed ring opening of electron-deficient alkylidenecyclopropanes (ACPs) to generate allylic phosphonium zwitterions that resemble the well-studied phosphine-allene adducts but exhibit distinct properties. The potent reactivity of these intermediates has been demonstrated in three types of substrate-controlled phosphine-catalyzed rearrangements of alkylidenecyclopropylketones, which chemoselectively afford tri- and tetrasubstituted furans, and trisubstituted dienones in good yields.

A three-component reaction between one molecule of phosphorus ylides (P-ylides) and two molecules of isocyanates for the rapid assembly of 2-amino-3-carboxylate-4-quinolones is described. The mechanism may involve the addition of a P-ylide to an isocyanate followed by 1,3-H shift to form a carbamoyl stabilized P-ylide. The intermediate then reacts with another aryl isocyanate via Wittig/ketenimine-ketene rearrangement/6π-electrocyclization/1,3-H shift to finally afford the 4-quinolones.

The copper-catalyzed cyclization of activated alkenes with cyclobutanone O-acyl oximes under redox-neutral conditions has been reported. This facile protocol provided an efficient approach to a variety of cyanoalkylated oxindoles and dihydroquinolin-2(1H)-ones with a broad substrate scope and excellent functional group tolerance. In this reaction, sequential C-C bond cleavage, radical addition, and cyclization processes were involved, wherein multiple bonds were constructed in a one-pot reaction. Mechanistic studies suggest that the reaction probably proceeded via a radical pathway.

A Cp*RhIII -catalyzed annulative carbooxygenation of challenging 1,1-disubstituted alkenes triggered by C-H activation of N-aryloxyacetamides has been established, which affords 2,3-dihydrobenzofuran derivatives with a quaternary carbon center in good to excellent yields under mild redox-neutral conditions. An amide group on the alkenes is essential for the process, and may inhibit the β-H elimination from C(sp3)-Rh species by saturating the rhodium center through coordination. Furthermore, mechanistic insights obtained from control experiments suggest a mechanism involving a RhIII -RhV -RhIII catalytic cycle.

The dihydroxylammonium 5,5′-bistetrazole-1,1′-diolate (TKX-50), as an outstanding representative of nitrogen-rich energetic salts, has recently attracted increasing interest due to its excellent performances. However, it is unclear about the photostability and degradation pathways of TKX-50 in aqueous solution. In this paper, the photostability and the degradation process of TKX-50 in aqueous solution have been comprehensively studied for the first time. TKX-50 can keep stable toward visible light. However, it presented a rapid degradation with rate constant of 0.0054 s−1 under 254-nm light irradiation. TKX-50 also demonstrated much faster photodegradation than traditional nitro explosives. Further, degradation products of TKX-50 were analyzed by high-resolution mass spectrum with theoretical calculations. The photodegradation pathways are proposed that 5,5′-bistetrazole-1,1′-diolate (BTO) anion of TKX-50 can been fragmented into the nitrile by losing N2 and HNO, and then hydroxylammonium (NH3OH+) from TKX-50 reacts with the nitrile through the nucleophilic addition. Besides as a solvent, water also may accelerate the photodegradation of TKX-50 probably by hydrolyzing the intermediary nitrile products. In a word, this study provides comprehensive understanding about the photostability of TKX-50 in aqueous solution, and it is helpful to study the photochemistry of other energetic ionic salts based on BTO.

Alkynylcyclopropanes have been used for the first time as coupling partners in transition-metal-catalyzed C–H functionalization. Specifically, a Cp*RhIII-catalyzed regioselective annulation of alkynylcyclopropanes with N-aryloxyamides via redox-neutral C–H/C–C activation has been developed, which affords highly functionalized 2,3-dihydrobenzofurans bearing an (E)-exocyclic carbon–carbon double bond and a tetra-substituted carbon center in moderate to good yields with a broad substrate scope.

A sustainable strategy by internally recycling an organocatalyst as a reactant in a downstream reaction to improve the atom efficiency of organocatalytic tandem reactions is described. Specifically, a one-pot tandem Cloke–Wilson/Boulton–Katritzky reaction of cyclopropylketones with a hydroxylamine has been developed for the synthesis of fully substituted isoxazoles, in which the hydroxylamine serves as both an upstream catalyst and a downstream reactant.

Efficient construction of quaternary carbon centers represents one of the most challenging goals in organic synthesis, and it has drawn tremendous research interest from organic chemist community. The past decade has witnessed a significant advancement of direct C-H functionalization, which delivers various synthetic tools for assembling structurally diversified architectures with the advantage of step- and atom-economy, operational simplicity, and readily available substrates. In this Minireview, synthetic methods based on transition-metal-catalyzed C-H functionalization as efficient tools for the construction of quaternary carbon centers are summarized.

In this Letter, we described a distinct DABCO-catalyzed [2+2] annulation reaction of allenoates with azodicarboxylates which affords 3-alkylidene-1,2-diazetidines in moderate yields with excellent stereo- and regioselectivity. This reaction constitutes the first example of Lewis base-catalyzed annulation of allenoates with azodicarboxylates, and showcases a divergent reactivity between phosphines and amines.

We report a phosphine-catalyzed activation of electron-deficient vinylcyclopropanes (VCPs) to generate an ambident C5 synthon that is poised to undergo consecutive reactions. The utility of the activation is demonstrated in a phosphine-catalyzed rearrangement of vinylcyclopropylketones to cycloheptenones in good yields with a broad substrate scope. Mechanistic investigations support a stepwise process comprising homoconjugate addition, water-assisted proton transfer, and 7-endo-trig SN 2' ring closure.

An organocatalytic Cloke–Wilson rearrangement of cyclopropyl ketones to 2,3-dihydrofurans is exploited utilizing the homoconjugate addition process. With 1,4-diazabicyclo[2.2.2]octane as the catalyst, the rearrangement in DMSO at 120 °C proceeded in generally high yields, exclusive regioselectivity, and a broad substrate scope. An examination of the mechanism including stereochemical analysis and intermediate isolation supports an SN1-type ring opening of the mechanism.

The condensation reaction of a γ-tert-butylallenoate, ethyl 5,5-dimethylhexa-2,3-dienoate, and aldehydes in the presence of sodium ethoxide is described. A range of aldehydes readily reacts with γ-tert-butylallenoate and ethoxide providing a straightforward synthesis of 1,2,3,4-tetrasubstituted conjugated dienes in moderate to good yields and exclusive E,E selectivity. For some aldehydes, the condensation chemoselectively delivers conjugated enynes in good yields and exclusive E selectivity.

A catalyst-free allylic alkylation of stabilized phosphorus ylides with allylic carbonates via a regioselective SN2' process is presented. Subsequent one-pot Wittig reaction with both aliphatic and aromatic aldehydes as well as ketenes provides structurally diverse skipped dienes (1,4-dienes) in generally high yields and moderate to excellent stereoselectivity with flexible substituent patterns. This one-pot SN2' allylation-Wittig strategy constitutes a convenient and efficient synthetic method for highly functionalized skipped dienes from readily available starting materials.

A highly regioselective SN2' Mitsunobu reaction between Morita–Baylis–Hillman (MBH) alcohols, azodicarboxylates, and triphenylphosphine is developed, which provides an easy access to α-alkylidene-β-hydrazino acid derivatives in high yields and good stereoselectivity. This reaction represents the first direct transformation of MBH alcohols into hydrazines.

A phosphine-catalyzed formal vinylogous aldol reaction of γ-methyl allenoates with aldehydes is herein reported, in which the γ-methyl group is directly involved in the carbon–carbon bond formation. Under the catalysis of triarylphosphine (20 mol %) and in the presence of a protic additive, γ-methyl allenoates and aldehydes chemo- and stereoselectively produce functionalized 1,3-dioxanes or dienols in modest to good yields. These chemical transformations provide easy excess to oxy-functionalized enoates and dienoates under very mild conditions.

A new BINOL-derived chiral bifunctional phosphine has been designed and successfully prepared, which features a cyclic substructure of 1,3,5-diazaphosphinane. This chiral phosphine possesses good air stability in solid state, and it can be conveniently used as a relatively more nucleophilic phosphine organocatalyst. Preliminary investigations showed that it could generally afford fair to excellent yields but only modest enantioselectivity in the (aza)-Morita–Baylis–Hillman reactions of activated olefins such as ethyl acrylate and methyl vinyl ketone with aldehydes or imines. [Supplementary materials are available for this article. Go to the publisher's online edition of Phosphorus Sulfer and Silicon and the Related Elements for the following free supplemental files: Additional text and figures.]

With over 5000 members isolated to date, sesquiterpene lactones represent a prolific source of medicinal agents with several derivatives in human clinical trials. The guaianolides, a major subset of this group, have been intensely investigated from both medicinal and chemical synthesis perspectives for decades. To date, the myriad stereochemical permutations presented by this enormous family have precluded the synthesis of many unique members. Herein we report the first total synthesis of the trans-fused 8,12-guaianolide (+)-mikanokryptin in 10 steps from (+)-carvone. Notably this represents the first gram-scale total synthesis of any guaianolide natural product.

The title [2 + 2] annulation reaction proceeds with excellent regio- and stereoselectivity to produce the corresponding 2-diazetidines in moderate yields.

An amine-catalyzed [4 + 2] annulation of Morita-Baylis-Hillman allylic acetates 2 with electron-deficient alkenes or diazenes has been developed for efficient syntheses of highly functionalized cyclohexenes, tetrahydropyridazines, and important spirocycles. This reaction unveils a new reactivity pattern of the intensely studied allylic compounds 2 acting as a C(4) synthon in Lewis base catalyzed annulation reactions and also showcases divergent catalysis between tertiary amines and phosphines.

As an extension of our previous studies, the phosphine-mediated diverse reactivity of γ-substituted allenoates with aldehydes has been further investigated. Under the catalysis of tris(p-chlorophenyl)phosphine (20 mol %), ethyl 2,3-pentadienoate, namely ethyl γ-methyl allenoate, readily undergoes a formal [4+2] annulation with dual-functional salicylaldehydes, giving highly functionalized chromans in 47–97% yields. This transformation represents a novel reactivity pattern of electron-deficient allenes with aldehydes. Conversely, when the γ substituent in the allenoate changes from methyl to benzyl or the employed phosphine from weakly nucleophilic triarylphosphine to strongly trialkylphosphine, the phosphine-mediated reactivity of γ-substituted allenoates with aldehydes will be steered to a stoichiometric olefination reaction, leading to the highly stereoselective formation of (E,E)-1,3-dienes. Thus, under the mediation of equivalent PPh3, ethyl γ-benzyl allenoate readily condenses with salicylaldehydes, affording (E,E)-1,3-dienes in 34–84% yields; with strongly nucleophilic 1,3,5-triaza-7-phosphaadamantane (PTA) used instead of PPh3, ethyl γ-methyl allenoate also gives the corresponding olefination products in 32–73% yields with reactive aromatic aldehydes. On the basis of our previous studies and current work, these chemical transformations of γ-substituted allenoates with aldehydes, as well as their diverse reactivity, have been mechanistically rationalized.

Phosphine-mediated olefination between alpha-substituted allenoates and aldehydes to form 1,2,3,4-tetrasubstituted 1,3-dienes is presented. High levels of chemo- and diastereoselectivity and yield are obtained for a wide scope of substrates with the choice of appropriate phosphines. This reaction evidences the capacity of phosphines in the control of reaction pathways and provides a highly efficient synthetic method for tetrasubstituted conjugated dienes.

Allenoates as an important class of electron-deficient allenes possess diverse reactivities, which have been extensively investigated in recent years. This review primarily summarizes recent advances in the tertiary phosphine-mediated (catalytic or stoichiometric) reactions between allenoates and aldehydes, which include annulations of 2,3-butadienoates with aldehydes, the [3+2] cycloaddition reaction and olefination between γ-substituted allenoates and aldehydes, vinylogous Wittig reaction and cyclopropanation of α-substituted allenoates with aldehydes, respectively. In light of those already accepted plausible mechanisms, rationalized are the differences in the reactivities of allenoates with different electrophiles including activated olefins, imines and aldehydes. In the reported chemical transformations, tertiary phosphines with inherent properties like nucleophilicity and deoxygenating ability play critical roles.