Palladium‐Catalyzed Construction of Heteroatom‐Containing π‐Conjugated Systems by Intramolecular Oxidative CH/CH Coupling Reaction

Synthesis of heteroatom‐containing ladder‐type π‐conjugated molecules was successfully achieved via a palladium‐catalyzed intramolecular oxidative C?H/C?H cross‐coupling reaction. This reaction provides a variety of π‐conjugated molecules bearing heteroatoms, such as nitrogen, oxygen, phosphorus, and sulfur atoms, and a carbonyl group. The π‐conjugated molecules were synthesized efficiently, even in gram scale, and larger π‐conjugated molecules were also obtained by a double C?H/C?H cross‐coupling reaction and successive oxidative cycloaromatization.     

Efficient and Z-selective cross-metathesis of conjugated enynes

[reaction: see text] The generation of a conjugated alkynyl alkylidene has been achieved using an allyl ether moiety as an intramolecular catalyst delivery vehicle. The reaction of this intermediate with alkenes and alkynes yields conjugated enynes with Z-selectivity.     

A conjugated alkyne functional bicyclic polybenzoxazine with superior heat resistance

A difunctional benzoxazine (coPh‐apa) with a conjugated alkyne group is synthesized by the oxidative coupling reaction from a monocycle‐benzoxazine (Ph‐apa) containing an alkyne group. A model compound, 1,4‐diphenylbutadiyne (coPa), is used to study the curing reaction process of coPh‐apa by DSC, Fourier transform infrared spectroscopy, and ¹³C NMR, and the results suggest that the conjugated alkyne groups are involved in the crosslinking reaction via the trimerization reaction of the conjugated alkynyl groups and the Diels–Alder reaction. Furthermore, thermal properties of the polybenzoxazine are studied by dynamic thermomechanical analysis and thermogravimetric analysis. A glass‐transition temperature (T_gs) of as high as 412 °C and a char yield of 75.6% at 800 °C under nitrogen are obtained with the aid of the conjugated alkyne groups. Its excellent heat resistance dominates most thermosetting resins and will serve for heat shields. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1587–1592     

Mechanistic Aspects of Monomer, Polymer Formation, and Synthesis of PQ-Alt-Dialkyl-fluorene Conjugated Copolymer

Suzuki coupling reaction is widely used in the construction of conjugated polymers; however, there is still no report describing the mechanism and coupling of 9,10-phenanthrenequinone（PQ） building blocks via Suzuki reaction because PQ is sensitive to bases and light. Herein is reported the efficient Suzuki coupling of PQ with 9,10-dialkylfluorene with Na2CO3 as basic species and high molecular weight PQ-Alt-Dialkyl-Fluorene conjugated copolymer obtained in an yield of 42%. Based on the characterization data and well-accepted literature, we proposed a step-by-step mechanistic explanation for the formation of the PQ containing alternating conjugated copolymer.     

Click To Bind: Metal Sensors

The copper‐catalyzed azide–alkyne “click” cycloaddition reaction is an efficient coupling reaction that results in the formation of a triazole ring. The wide range of applicable substrates for this reaction allows the construction of a variety of conjugated systems. The additional function of triazoles as metal‐ion ligands has led to the click reaction being used for the construction of optical sensors for metal ions. The triazoles are integral binding elements, which are formed in an efficient modular synthesis. Herein, we review recent examples of triazoles as a metal‐binding element in conjugated metal‐ion sensors.     

Rapid access to the synthesis of polysubstituted δ-lactones via tandem stereoselective conjugate addition/α-alkylation of unsaturated 7,3-lactone-α-d-xylofuranose derivative

α-d-xylo-7,3-Unsaturated lactone, a versatile chiral building block, undergoes Cu-catalyzed conjugated addition with high yield and stereoselectivity. When the conjugated reaction is quenched with a suitable alkyl halide, a tandem stereoselective conjugated/α-alkylation reaction is achieved. Further, selective hydrolysis of the 1,2-O-isopropylidene moiety followed by oxidative cleavage and reduction reaction, afforded the title compounds.     

Stereoselective Synthesis of Substituted 1,3,5,7,9-Decapentaenes

Conjugated 1,3,5,7,9-decapentaene is an important structural unit in various of natural products such as phytoene, aurenin, vitamin At and A2[1]. It has been shown that conjugated polyenes are potentially useful compounds for non-linear optical materials. In the meantime the study of well-defined molecules has advanced into a strong field on its own right, because of the promising electronic and optical properties of these compounds[2]. It also attracts the interests of physical chemists as a calculation model[3] during the past decades. In the literature, there are only a few general strategies for the stereocontrolled construction of the decapentaene unit. This is mainly due to the instability and the facile (E)-(Z) isomerization of pentaene system. Synthetic methods for the construction of conjugated decapentaenes relied on the Wittig olefination[4], the Heck coupling reaction[5], the mixed crossed aldol condensation between conjugated esters and aldehydes[6], opening reaction of fulvalene complexes[7]. In our previous studies[8] on stereoseletive synthesis of polyene, we reported that conjugated trienes and enediynes could be prepared by our modified Ramberg-Backlund reaction from corresponding diallylic sulfones and dipropagylic sulfones. This synthetic method was applied to the synthesis of natural products containing a conjugated triene unit such as Galbanolenes. Reported here are our finding that bis-dienylic sulfones when submitted our Ramberg-Backlund conditions, provide decapentaenes in good yield. We use this synthetic method to synthesize 1,3,5,7,9-dec apentaene.     

Synthesis of Ethyl 2-Cyano-3-Methylthio-3'-Arylaminoacrylate From Low Nucleophilic Amine

The synthesis of ketene N,S-acetals has attracted a considerable attention as building blocks in organic synthesis, especially in the preparation of heterocycles^[1]. The addition reaction of ketene S,S-acetals with highly nucleophilic amines, such as alkylamines, can easily afford the corresponding ketene N,S-acetals, under gentle condition, which could be converted into conjugated ketene aminals by reaction with a second equivalent of the same or a different amine^[2,3]. However, this addition reaction with low nucleophilic amines, such as arylamine or heterocyclic amine, can hardly give the corresponding ketene N,S-acetals under gentle conditions. If under powerful condition,such as refluxing, the addition reaction affords a mixture of the N,S-acetals and conjugated ketene aminals^[4]. Recent studies showed that this addition reaction with low nucleophilic amines affords the corresponding ketene N,S-acetals in the presence of a catalyst^[5].     

Decomposition d'hypobromites prepares par action de l'oxyde de mercure et du brome sur des alcools bicycliques pontes

Hydrobromites of bridged bicyclic alcohols have been decomposed to yield tetrahydrofuran-type ethers as well as fragmentation products. The latter results from the cleavage of the carbon-carbon bond α, β to the hydroxyl group. In the case of 3-hydroxy-3-methyl bicyclo[3.2.1]octane, conjugated ketones and brominated olefins are formed, whereas tetrahydrofuran-type ethers are formed only under different experimental conditions different from those applicable to general cases. The reaction mechanisms have been established. The influence of the various reaction parameters has been studied in order to obtain selectively either tetrahydrofuran-type ethers or a mixture of conjugated ketones and brominated olefins.     

含联苯PPV类共轭聚合物的合成及荧光性能研究

在催化剂聚氯乙烯-四乙烯五胺负载钯配合物(PVC-TEPA-Pd)的作用下,利用Heck反应,二碘联苯与苯乙烯反应可以得到4,4′-二苯乙烯基联苯。进一步用二碘联苯和二乙烯基苯反应可以成功地将联苯基元引入聚合物主链,得到一种新型的含联苯结构的PPV类共轭聚合物,通过红外光谱对聚合物结构进行了表征,并对聚合物的荧光性能进行了研究,发现其荧光发射光谱峰位于500nm,与4,4′-二苯乙烯基联苯荧光发射光谱峰相比,发生了明显的红移。由于分子结构中存在较大共轭体系,两种物质在多种溶剂中的溶解性均较差。     

Efficient organocatalyzed solvent-free selective synthesis of conjugated enones

A series of conjugated dienones and enones were synthesized by a reaction of both conjugated and simple aldehydes, respectively, with 1,3-dicarbonyl compounds and aldehydes under solvent-free conditions at room temperature in the presence of 10 mol % of l-proline as catalyst. The selective formation of one isomer was observed exclusively with most of the 1,3-dicarbonyl compounds and aldehydes. The most commonly formed xanthene derivative from the cyclic diketones is inhibited with our protocol, with the exclusive formation of conjugated dienones only.     

Regioselective Synthesis of Nanographenes by Photochemical Cyclodehydrochlorination

Novel nanographenes were prepared by a photochemical cyclodehydrochlorination (CDHC) reaction. Chlorinated precursors were irradiated in acetone in the presence of a base or in pure benzene and underwent multiple (up to four) regioselective cyclization reactions to provide rigid π‐conjugated molecules. Pure compounds were recovered in good yields by simple filtration at the end of the reaction. The CDHC reaction showed compatibility with both electron‐poor and electron‐rich substrates, thus allowing the synthesis of pyridine‐ and thiophene‐fused nanographenes. It also enabled the synthesis of sterically hindered contorted π‐conjugated molecules without causing full aromatization. A kinetic study showed that the CDHC reaction under the conditions used is a very fast process, and some reactions are completed within minutes. The CDHC reaction thus shows great potential as an alternative to other reactions involving harsher conditions for the preparation of nanographenes.     

Palladium-catalyzed cycloisomerisation reaction of 1,6-enyne acetic esters to form five-membered nitrogenated heterocyclic conjugated trienes

A palladium-catalyzed cycloisomerisation reaction of 1,6-enyne acetic esters have been developed. This cyclization reaction shows excellent regioselectivity and good functional group tolerance to obtain five-membered nitrogenated heterocyclic conjugated trienes in moderate to excellent yields. The resulting conjugated trienes could be facilely converted to highly substituted benzenes through Diels-Alder reactions.     

Double diels-alder reactions of linear conjugated tetraenes

[reaction: see text] Linear conjugated tetraenes are shown to participate effectively as bis-dienes in sequences involving either two intermolecular Diels-Alder reactions or an intramolecular followed by an intermolecular Diels-Alder reaction. Thus, simple tetraenol 1 is transformed into tetracyclic products 5, 6, and 9 in high yielding and highly stereoselective sequences with maleic anhydride involving the formation of three rings, four C-C bonds and one C-O bond, and eight stereocenters. In the latter case, the one-pot reaction protocol is very simple, and furnishes a single diastereoisomeric product in essentially quantitative yield. Linear conjugated tetraenes exhibit complete terminal site selectivity in reactions with dienophiles and computational investigations reveal that two discrete pi-conjugative interactions are the origin of this unexpected reactivity. B3LYP/6-31G(d) transition structures also allow an explanation of unexpectedly high pi-diastereofacial selectivities witnessed during these transformations, through the identification of preferred C1-C diene conformations and nonbonded interactions. These new experimental and computational findings encourage the use of linear conjugated polyenes in domino sequences.     

Synthetic and theoretical studies on the reduction of electron withdrawing group conjugated olefins using the Hantzsch 1,4-dihydropyridine ester

The Hantzsch 1,4-dihydropyridine ester (1) has been observed to be a useful selective reducing agent for the reduction of electron-withdrawing conjugated double bonds. The rate of this reaction was observed to be dependent upon the nature of the conjugated substituents and, consequently, the electronic nature of the unsaturated double bond. Theoretical calculations confirmed the importance of the HOMO-LUMO gap for this reaction and implicated a hydride transfer, agreeing with the experimentally observed reaction rate order. The calculations also revealed the importance of a boatlike structure of the 1,4-dihydropyridine nucleus as well as a trans arrangement of the ester groups to facilitate the hydride transfer.     

Synthesis and photophysical properties of phenothiazine-labeled conjugated dendrimers

A novel class of conjugated dendrimers bearing phenothiazines as peripheral groups and phenylenevinylene-group as a core has been synthesized through the Wittig-Horner reaction in moderate to good yield.     

Conjugated polymers for photocatalysis

The photocatalytic properties of the conjugated polymers have been investigated for the first time. Degradation of various textile dyes such as Alizarin S, Alizarin G, Orange G, and Remazol brilliant blue were studied under UV radiation. The experimental data indicated that the photocatalytic activity of the conjugated polymers was significantly higher than that of Degussa P-25 under similar conditions. The conjugated polymers were characterized by photoluminescent, UV-visible, and IR spectroscopies before and after photocatalytic reactions. The degradation of phenol was also carried out to study the reaction pathway of degradation.     

Photoinduced addition of phthalimide to unactivated alkynes

Photoexcited phthalimide in equilibrium with its conjugated base produces the regioselective hydrophthalimidation of conjugated alkynes. The vinylphthalimide thus obtained is hydrolyzed to the corresponding carbonyl compound. With unconjugated alkynes, the outcome is a double addition of phthalimide to the triple bond. The reaction is assumed to take place via single electron transfer from either the alkyne or the phthalimide anion to the excited phthalimide as the primary photoprocess.     

Development of a liquid chromatography-tandem mass spectrometry method for the identification of natural androgen steroids and their conjugates in urine samples

An analytical procedure for the determination of natural steroids and their conjugates was developed and applied to bovine and human urine. Fifteen compounds (free and conjugated) after extraction by solid-phase were identified by liquid chromatography-tandem mass spectrometry (LC-MS-MS) in multiple reaction monitoring (MRM). Free and conjugated steroids were detected all together in the same chromatographic analysis respectively in positive and negative ionization. This procedure reveals to be time-saving, because it overcomes the need of further sample pre-treatment steps, such as enzymatic hydrolysis and derivatisation.The recovery for each compound was around 80%. Limit of detection of each steroid free or conjugated has been evaluated.     

Sensitized photo-oxygenation of acyclic conjugated dienes

Sensitized photo-oxygenation of a wide variety of acyclic 1,3-dienes was investigated. The 1,4-cycloaddition of singlet oxygen to acyclic conjugated dienes was closely related to the thermal Diels-Alder reaction in stereospecificity, and steric and electronic effects of substituents. Reactivity order of singlet oxygen toward conjugated dienes and isolated C—C double bonds was exhibited as follows: trisubstituted mono-olefins > 2-substituted 1,3-dienes > disubstituted mono-olefins.