Blue-Emitting Ligand-Mediated Assembly of Rare-Earth MOFs toward White-Light Emission, Sensing, Magnetic, and Catalytic Studies

New lanthanide carboxylate compounds with two- (2D) and three-dimensional (3D) structures have been prepared by employing 2,5-bis(prop-2-yn-1-yloxy)terephthalic acid (2,5-BPTA) as an organic linker. The compounds, [Ln(C₁₄H₈O₆)(C₇O₃H₄)·2H₂O]·4(H₂O), Ln = Y, Pr, Nd, Sm, Eu, Gd, Tb, Dy and [Ln(C₇O₃H₄)₃·(C₃H₇ON)·(H₂O)]·2(H₂O)(C₃H₇NO), Ln = La, Ce, Pr, have two- and three-dimensional structures, respectively. In all compounds, lanthanide ions are connected together, forming a dimer, which is connected by the 2,5-BPTA ligand. In the two-dimensional structure, there are two 2,5-BPTA moieties present, and in the three-dimensional structure, there are three 2,5-BPTA moieties present. The lanthanide centers are nine-coordinated, the 2D structure has a tricapped trigonal prismatic arrangement, and the 3D structure has a monocapped distorted square antiprismatic arrangement. The Pr compound forms in both 2D and 3D structures, whose formation depends on the time of the reaction (2 days─2D and 5-6 days─3D). The ligand emits in the blue region, and using the characteristic emission of Eu³⁺ (red) and Tb³⁺ (green) ions, we achieve white light emission in the (Y_0.96Tb_0.02Eu_0.02) compound. The overall quantum yield for the white light emission is 28%. The strong green luminescence of the Tb³⁺-containing compound was employed to selectively sense the Cr³⁺ and Fe³⁺ ions in aqueous solution with limits of detection (LODs) at 0.41 and 8.6 ppm, respectively. The Tb compound was found to be a good heterogeneous catalyst for the Ullman-type O-arylation reaction between phenol and bromoarene with yields of 95%. Magnetic studies on the Gd-, Tb-, and Dy-containing compounds showed weak exchange interactions within the dimeric Ln₂ units. The present work demonstrates the many utilities of the rare-earth-containing MOFs, especially toward white-light emission, metal-ion sensing, and heterogeneous catalysis.

Redox Isomerization/(3+2) Allenoate Annulation by Auto-Tandem Phosphine Catalysis

A phosphine-catalyzed approach to pyrrolines has been developed that involves two mechanistically unlinked catalytic processes. The first involves the redox isomerization of amino crotonates to provide access to aliphatic tosyl imines, which then engage in a (3+2) annulation with various allenoates. The reaction shows generality, with 24 examples established, along with a low yielding and moderately enantioselective variant. Mechanistic studies indicate that the viability of the process is linked to the selection of catalysts with similar propensity to add to the two coupling partners.

Recent advances in continuous-flow organocatalysis for process intensification

The progresses on continuous-flow organocatalysis from 2016 to early 2020 are reviewed with focus on transition from batch to flow.

Synthesis of (E,E)-Dienones and (E,E)-Dienals via Palladium-Catalyzed γ,δ-Dehydrogenation of Enones and Enals

A new strategy for the synthesis of conjugated (E,E)-dienones and (E,E)-dienals via a palladium-catalyzed aerobic γ,δ-dehydrogenation of enones and enals has been developed. The method can be employed in the direct and efficient synthesis of various (E,E)-dienones and (E,E)-dienals, including non-substituted α-, β-, and γ- and/or δ-substituted (E,E)-dienones and (E,E)-dienals. The protocol is featured by the ready accessibility and elaboration of the starting materials, good functional group compatibility, and mild reaction conditions. Furthermore, the reaction is of complete E,E-stereoselectivity and uses molecular oxygen as the sole clean oxidant.

The 6π-azaelectrocyclization of azatrienes. Synthetic applications in natural products, bioactive heterocycles, and related fields

Covering: 2006 to 2018 The application of the 6π-azaelectrocyclization of azatrienes as a key strategy for the synthesis of natural products, their analogs and related bioactive or biomedically-relevant compounds (from 2006 to date) is comprehensively reviewed. Details about reaction optimization studies, relevant reaction mechanisms and conditions are also discussed.

Ph3P promoted one-pot synthesis of dialkyl 2-(2-oxopyridin-1(2H)-yl)but-2-enedioates from a reaction of 2-hydroxypyridine and dialkyl acetylenedicarboxylates

2-Hydroxypyridine undergoes a smooth reaction with dialkyl acetylenedicarboxylates in the presence of triphenylphosphine (15 mol%) to produce the E/Z isomers of dialkyl 2-(2-oxopyridin-1(2 H)-yl)but-2-enedioates in high yields.

Phosphine Organocatalysis

The hallmark of nucleophilic phosphine catalysis is the initial nucleophilic addition of a phosphine to an electrophilic starting material, producing a reactive zwitterionic intermediate, generally under mild conditions. In this Review, we classify nucleophilic phosphine catalysis reactions in terms of their electrophilic components. In the majority of cases, these electrophiles possess carbon-carbon multiple bonds: alkenes (section 2), allenes (section 3), alkynes (section 4), and Morita-Baylis-Hillman (MBH) alcohol derivatives (MBHADs; section 5). Within each of these sections, the reactions are compiled based on the nature of the second starting material-nucleophiles, dinucleophiles, electrophiles, and electrophile-nucleophiles. Nucleophilic phosphine catalysis reactions that occur via the initial addition to starting materials that do not possess carbon-carbon multiple bonds are collated in section 6. Although not catalytic in the phosphine, the formation of ylides through the nucleophilic addition of phosphines to carbon-carbon multiple bond-containing compounds is intimately related to the catalysis and is discussed in section 7. Finally, section 8 compiles miscellaneous topics, including annulations of the Hüisgen zwitterion, phosphine-mediated reductions, iminophosphorane organocatalysis, and catalytic variants of classical phosphine oxide-generating reactions.

Palladium-catalysed atom-economical synthesis of conjugated dienals from terminal acetylenes and acrolein

Conjugated (E,E)-dienals are versatile synthetic intermediates owing to their trifunctional, electrophilic nature and the prevalence of the (E,E)-diene in a wide range of functional molecules. It is shown herein that (E,E)-dienals can be readily prepared in two palladium-catalysed steps from simple, unactivated starting materials; terminal acetylenes and acrolein can be coupled via conjugate addition, followed by alkyne isomerisation. This procedure provides a highly atom-economical, redox-neutral and practical method to prepare a range of conjugated (E,E)-dienals in good yields and diastereoselectivities.

Lu's [3 + 2] cycloaddition of allenes with electrophiles: discovery, development and synthetic application

The discovery of Lu's [3 + 2] cycloaddition reaction is briefly introduced, and the recent important developments and synthetic applications of Lu's [3 + 2] cycloaddition reaction are highlighted and overviewed.

Redox cycloisomerization approach to 1,2-dihydropyridines

The phosphine-catalyzed synthesis of 1,2-dihydropyridines via an alkyne isomerization/electrocyclization sequence is described. Propargylidenecarbamate substrates were prepared following a one-pot procedure between a terminal alkyne, a benzonitrile, and a chloroformate in the presence of trimethylaluminum. This methodology gives access to a diverse set of 2,6-disubstituted 1,2-dihydropyridines in high yield. The products can be easily converted into substituted piperidines or pyridines, and this methodology was applied to the synthesis of indolizidines.

In situ intramolecular catalytic 1,2-addition of allenoates to cyclic ketones towards polycyclic allenoates

Sequential deprotonation, isomerization of 3-alkynoates and subsequent 1,2-addition led to bicyclic allenoate in the presence of a catalytic amount of Cs₂CO₃.

Asymmetric isomerization of ω-hydroxy-α,β-unsaturated thioesters into β-mercaptolactones by a bifunctional aminothiourea catalyst

We present a novel methodology for the asymmetric synthesis of β-mercaptolactones via isomerization of ω-hydroxy-α,β-unsaturated thioesters by means of a bifunctional aminothiourea catalyst. The catalyst interacts with the substrate through the cooperative action of both a covalent bond at the amino group and noncovalent bonding at the thiourea group. The potential for an enantiodivergent synthesis could also be demonstrated by carrying out the reaction in a different solvent system.

Regiodivergent synthesis of 1- and 2-arylsulfonyl 1,3-dienes

In the course of a study of the alkoxyallylation of allenic sulfones through the use of π-allylpalladium chemistry, we discovered an isomerization of allenic sulfones to arylsulfonyl 1,3-dienes. Under conditions of palladium catalysis in the presence of acids such as acetic acid, allenic sulfones are converted to 1-arylsulfonyl 1,3-dienes. On the other hand, nucleophilic catalysis using triphenylphosphine in the presence of a proton shuttle yields 2-arylsulfonyl 1,3-dienes. Thus, either regioisomer of the arylsulfonyl diene can be prepared at will based on changes in reaction conditions.

Catalytic asymmetric C-N bond formation: phosphine-catalyzed intra- and intermolecular γ-addition of nitrogen nucleophiles to allenoates and alkynoates

Pin the amine on the gamma: A new method has been developed for the γ-addition of nitrogen nucleophiles to γ-substituted alkynoates or allenoates through intra- and intermolecular processes that are catalyzed by spirophosphine 1. An asymmetric version of this reaction affords enantioenriched pyrrolidines, indolines, and γ-amino-α,β-unsaturated carbonyl compounds.

On the isomerization of cyclooctyne into cycloocta-1,3-diene: synthesis, characterization and structure of a dinuclear platinum(II) complex with a μ-η2:η2-1,3-COD ligand

The Zeise's salt type cyclooctyne compound [K(18C6)][PtCl(3)(COC)] (1; COC = cyclooctyne; 18C6 = 18-crown-6) was found to react in chloroform solution at room temperature within several weeks yielding the dinuclear cyclooctadiene compound [K(18C6)](2)[(PtCl(3))(2)(μ-η(2):η(2)-1,3-COD)] (2; 1,3-COD = cycloocta-1,3-diene) and non-coordinated cycloocta-1,3-diene. The identity of 2 was confirmed by microanalysis, NMR spectroscopy ((1)H, (13)C) and electrospray ionization mass spectrometry (ESI-MS). A single-crystal X-ray diffraction analysis of 2 exhibited a bridging μ-η(2):η(2)-cycloocta-1,3-diene ligand with non-conjugated double bonds each coordinated to a PtCl(3) fragment. On the basis of DFT calculations as well as energy decomposition analyses (EDA), charge decomposition analyses (CDA) and natural bond orbital (NBO) analyses the peculiarities of the nature of the Pt-C bonds in the dinuclear complex anion [(PtCl(3))(2)(μ-η(2):η(2)-1,3-COD)](2-) (2a') compared with those in mononuclear olefin complexes of Zeise's salt type [PtCl(3)L](-) (L = η(2)-1,3-COD, 3a'; cis-but-2-ene, 4a'; COE, 5a'; COE = cyclooctene) are discussed. Furthermore, the driving force for the strongly exergonic reaction with formation of the cyclooctadiene complex 2a' was found to be a significant release of ring strain of the cyclooctyne ligand in the starting compound 1.

Recent advances in stereoselective synthesis of 1,3-dienes

The aim of this review is to present the latest developments in the stereoselective synthesis of conjugated dienes, covering the period 2005-2010. Since the use of this class of compounds is linked to the nature of their appendages (aryls, alkyls, electron-withdrawing, and heterosubstituted groups), the review has been categorized accordingly and illustrates the most representative strategies and mechanisms to access these targets.

An efficient and practical entry to 2-amido-dienes and 3-amido-trienes from allenamides through stereoselective 1,3-hydrogen shifts

Preparations of de novo acyclic 2-amido-dienes and 3-amido-trienes through 1,3-hydrogen shifts from allenamides are described. These 1,3-hydrogen shifts could be achieved thermally or they could be promoted by the use of Brønsted acids. Under either condition, these processes are highly regioselective in favour of the α-position, and highly stereoselective in favour of the E-configuration. In addition, 6π-electron electrocyclic ring-closure could be carried out with 3-amido-trienes to afford cyclic 2-amido-dienes, and such electrocyclic ring-closure could be rendered in tandem with the 1,3-hydrogen shift.

P-Acylphosphonium salts and their vinyloges — application in synthesis

Review with 101 refs. of progress in synthetic applications and properties of P-acylphosphonium salts including acylation via P-acylphosphonium salts, enantioselective acylation using chiral phosphine ligands, nucleophilic (β)-oniovinylation, and reaction involving vinyloges of P-acylphosphonium salts formed by treatment conjugated alkenoates or alkynoates with phosphines.

Regio- and stereoselective isomerizations of allenamides: synthesis of 2-amido-dienes and their tandem isomerization-electrocyclic ring-closure

A regio- and stereoselective isomerization of allenamides is described, leading to preparations of de novo 2-amido-dienes and a tandem isomerization-6pi-electron electrocyclic ring-closure.

Efficient highly selective synthesis of methyl 2-(ethynyl)alk-2(E)-enoates and 2-(1'-chlorovinyl)alk-2(Z)-enoates from 2-(methoxycarbonyl)-2,3-allenols

Highly regio- and stereoselective reactions of readily available 2-(methoxycarbonyl)-2,3-allenols 1 with oxalyl chloride in the presence of Et(3)N or DMSO afforded methyl 2-(ethynyl)alk-2(E)-enoates (E)-2 and 2-(1'-chlorovinyl)alk-2(Z)-enoates (Z)-3, respectively, in moderate to good yields.

Synthesis of Alkyl 2-[2-oxopyridin-1(2H)-yl]acrylates by Nucleophilic Addition of Alkyl Propiolates Catalysed by Ph3P

2-Hydroxypyridine undergoes a smooth reaction with alkyl propiolates in the presence of triphenylphosphine (15 mol%) to produce the corresponding alkyl 2-[2-oxopyridin-1(2H)-yl]acrylates in good yields. When the reaction was performed by 2-hydroxyquinoline and 2-hydroxyisoquinoline similar α-substituted alkyl acrylates were obtained.

An atom-economic and selective ruthenium-catalyzed redox isomerization of propargylic alcohols. An efficient strategy for the synthesis of leukotrienes

Catalytic ruthenium complexes in conjunction with an indium cocatalyst and Bronsted acid isomerize primary and secondary propargylic alcohols in good yields to provide trans enals and enones exclusively. Readily available indenylbis(triphenylphosphine)ruthenium chloride, in the presence of indium triflate and camphorsulfonic acid, gives the best turnover numbers and reactivity with the broadest range of substrates. Deuterium labeling experiments suggest that the process occurs through propargylic hydride migration followed by protic cleavage of the resultant vinylruthenium intermediate. Application of this method to the synthesis of leukotriene B4 demonstrates its utility and extraordinary selectivity.

Synthetic studies on macrolactin A: construction of C4-C24 fragment

The preparation of the C4-C24 fragment of the macrolactin A is described. The adopted synthetic strategy involves two isomerizations to selectively construct the (8E,10Z) and (16E,18E) dienes, using a sequential Claisen rearrangement/allene isomerization and a Ph3P-catalyzed isomerization of an yne-one, respectively.