Titanocene and zirconocene σ-alkynyl complexes in C---C single bond coupling and cleavage reactions

Group 4 metallocene mono- and bis-σ-alkynyl complexes of the type L₂M(σ-CCR) and L₂M(σ-CCR)₂ with M=titanium and zirconium in the oxidation states +3 and +4 and L=Cp (η⁵-cyclopentadienyl) and Cp^* (η⁵-pentamethylcyclopentadienyl) are important compounds for stoichiometric and catalytic C---C single bond coupling and cleavage reactions. Detailed investigations show five-membered metallacyclocumulenes L₂M(η⁴-1,2,3,4-RC₄R) as the key intermediates in both reactions of a C---C single bond cleavage of different 1,4-substituted 1,3-butadiynes RCC---CCR to alkynyl groups and the opposite reaction of C---C single bond formation starting from alkynyl groups under the formation of 1,4-substituted 1,3-butadiynes. Depending on different metals M and ligands L, coupling or cleavage is favoured. Combination of both reactions offered the first C---C single bond metathesis in homogeneous solution, which is photocatalyzed and titanocene-mediated. It proceeds via titanocene–mono-alkynyl complexes, which are interesting species also for other stoichiometric and catalytic C---C coupling reactions. Some similarities regarding the σ-to-π conversion exist between the coupling of the alkynyl groups at titano- and zirconocenes to complexed 1,3-butadiynes on one side and the coupling of phenyl groups at chromium to complexed diphenyl on the other side.     

A general approach to arylated furans,pyrroles, and thiophenes

A general and practical synthetic method for aryl-substituted five-membered heterocycles has been developed. In the presence of KOH (30%), 1,4-diaryl-1,3-butadiynes undergo the cyclocondensation reaction with water, primary amines, and Na₂S·9H₂O in DMSO at 80 °C to afford 2,5-diarylfurans, 1,2,5-trisubstituted pyrroles, and 2,5-diarylthiophenes in good to high yields. Further studies have disclosed that aryl-substituted five-membered heterocycles can be also synthesized by a one-pot, two-step strategy from the terminal alkynes in DMSO firstly catalyzed by CuCl, and then via addition of KOH to promote the cyclocondensation of 1,3-butadiynes generated in situ.     

One-pot synthesis of partially fluorinated naphthalene, anthracene, and chrysene derivatives

A series of partially fluorinated naphthalene, anthracene, and chrysene derivatives have been synthesized by a convenient one-pot reaction of multi-fluorinated aromatics and 1,4-dilithio-1,2,3,4-tetraaryl-1,3-butadiene that was generated in situ from the reduction of diphenylacetylene derivatives with lithium naphthalenide.     

Bis(heterocumulenes) derived from the 1,4-diphenyl-1,3-butadiyne framework. Synthesis of three new classes of axially chiral biheteroaryls

Bis(ketenimines) and bis(carbodiimides) derived from 1,4-bis(2-aminophenyl)-1,3-butadiynes via two independent biradical cyclizations provided, respectively, axially chiral bis(benzocarbazoles) and bis(quinindolines). Mixed biheteroaryls, consisting of benzocarbazole and quinindoline units, have been also prepared by a slightly modified strategy.     

Partially fluorinated naphthalene derivatives from 1,4-dilithio-1,3-dienes and C6F6

Multi-substituted partially fluorinated aromatic compounds, such as naphthalene derivatives could be readily prepared by the reaction of 1,4-dilithio-1,3-dienes with hexafluorobenzene via double nucleophilic substitution. When these dilithium reagents were treated with hexachlorobenzene, chloropentafluorobenzene or bromopentafluorobenzene, chlorine-lithium or bromine-lithium exchange reactions, instead of nucleophilic substitution, took place.     

Photo-Fries rearrangement: Rearrangement of benzoyloxy compounds

Photo-Fries migration of the benzoyl group in 1-benzoyloxy-5-methoxy naphthalene, 1,4-dibenzoyloxy-2-methyl naphthalene, 1,4-dibenzoyloxy naphthalene, 1,5-dibenzoyloxy naphthalene, 8-benzoyloxy quinoline, 1,2-dibenzoyloxy benzene, 1,3-dibenzoyloxy benzene, and 1,4-dibenzoyloxy benzene afforded the corresponding mono and di-C-benzoyl products.

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Photo-Fries-Umlagerung: Umlagerung von Benzoyloxy-Verbindungen

Zusammenfassung Die Photo-Fries-Wanderung der Benzoylgruppe in 1-Benzoyloxy-5-methoxynaphthalin, 1,4-Dibenzoyloxy-2-methylnaphthalin, 1,4-Dibenzoyloxy-naphthalin, 1,5-Dibenzoyloxynaphthalin, 8-Benzoyloxychinolin, 1,2-Dibenzoyloxybenzol, 1,3-Dibenzoyloxybenzol und 1,4-Dibenzoyloxybenzol ergab die entsprechenden Mono- und Di-C-Benzoyl-Produkte.

     

A palladium-promoted route to 3-alkyl-4-(1-alkynyl)-hexa-1,5-dyn-3-enes and/or 1,3-diynes

Reaction of benzene solutions of arylacetylenes with 1 equiv. of chloroacetone and 2 equiv. of Et₃N, using a mixture of (PPh₃)₄ Pd and CuJ as catalyst, affords 1,4-diaryl-butadiynes in very good yields. Under similar reaction conditions aliphatic 1-alkynes yield mixtures of simmetrically disubstituted 1,4-dialkyl-1,3-butadiynes and of 3-alkyl-4-(1-alkynyl)-hexa-1,5-diyn-3-enes.     

Perthio- and perseleno-1,3-butadienes, -but-1-ene-3-ynes,and -[3]-cumulenes: one-step syntheses from 1,4-dilithio-1,3-butadiyne

[reaction: see text] Treatment of 1,4-dilithio-1,3-butadiyne (1) with dichalcogenides RSSR or RSeSeR affords dithio- and diseleno-1,3-butadiynes (2, 3), perthio- and perseleno-[3]-cumulenes (4, 5), perthio- and perseleno-1,3-butadienes (6, 7), and/or perthio- and perseleno-but-1-ene-3-ynes (8, 9). The products can be controlled by stoichiometry and temperature, by the presence or absence of oxygen, and by choice of the "R" group. By X-ray crystallography, hexa(methylthio)-1,3-butadiene is highly twisted, with a torsion angle [Phi(CCCC)] of 84.7 degrees and an elongated C(2)-C(3) distance of 1.484(3) A.     

Impact on the mesophase transition temperatures of 1,4-bis(naphthyl)-1,3-butadiyne of the attachment of terminal alkoxy chains

The synthesis of 1,4-bis(2-naphthyl)-1,3-butadiynes, containing terminal alkoxy chains, is reported. The mesomorphism of these compounds has been characterized by differential scanning calorimetry and polarizing optical microscopy. The introduction of terminal alkoxy chains, significantly lowers the melting temperature of the analogous core without terminal chains. The induction of a smectic phase occurred when two decyloxy chains were attached. The solid state structures and packing arrangements of the butyloxy derivative and the chainless core were determined by single crystal X-ray diffraction, and revealed greater layer interpenetration for the substituted material.     

An Efficient Four‐component Reaction for the Synthesis of Spiroheterocyclic Compounds

A series of 6‐amino‐8‐aryl‐3,4‐dihydro‐1H‐spiro[naphthalene‐2,2'‐[1,3] dioxolane]‐5,7‐dicarbonitrile and 8‐arylidene‐4‐aryl‐7,8‐dihydro‐5H‐spiro[quinazoline‐6,2'‐[1,3] dioxolan]‐2‐amine derivatives have been synthesized from the reactions of 1,4‐dioxaspiro[4.5] decan‐8‐one, aromatic aldehydes, and malononitrile (or guanidine carbonate) under different conditions with high yields. In this research, it was found the DBU–THF was efficient reaction condition for obtaining 6‐amino‐8‐aryl‐3,4‐dihydro‐1H‐spiro[naphthalene‐2,2'‐[1,3]dioxolane]‐5,7‐dicarbonitrile derivatives, while 95% EtOH and NaOH was the preferred condition for the synthesis of 8‐rylidene‐4‐aryl‐7,8‐dihydro‐5H‐spiro[quinazoline‐6,2'‐[1,3]dioxolan]‐2‐amine derivatives. To the best of our knowledge, these Spiroheterocycles were first reported in our research. The other advantages of this process were short‐reaction time, wide scope substrates, and simple set‐up.     

Highly efficient synthesis of stereodefined multisubstituted 1,4-dicyano- and 1-cyano-1,3-butadienes and their reactions with organolithium reagents

Stereodefined multisubstituted 1-cyano- and 1,4-dicyano-1,3-butadiene derivatives were obtained in excellent yields of the isolated product from their corresponding monohalo- and dihalobutadienes and CuCN. This reaction proceeded with high stereoselectivity and retention of the stereochemistry of the starting halobutadienes. A study of the utility of the thus-obtained 1-cyano- and 1,4-dicyano-1,3-butadiene derivatives was demonstrated by their reactions with organolithium reagents. 2H-Pyrrole or iminocyclopentadiene derivatives were formed in high yields from 1-cyano-4-halo-1,3-butadienes and organolithium reagents. When 1,4-dicyano-1,3-butadienes were treated with organolithium reagents followed by trapping with electrophiles, a tandem process took place to afford 2H-pyrrolyl nitriles in excellent yields. Reduction of 1,4-dicyano-1,3-butadiene derivatives with LiAlH4 showed novel reaction patterns relative to normal nitriles.     

Convenient Synthesis of N-Benzyl-1,4-dihydropyridines, Cyclohexenones, and Bicyclo[3.3.1]nonan-3-one Derivatives from 1-Aza-1,3-butadienes

Readily available 1-aza-1,3-butadienes (enimines) react with methyl acetoacetate and acetylacetone in the presence of catalytic amounts of lithium iodide to form in high yields unsymmetrically substituted 1,4-dihydropyridines or cyclohexenones. The reaction pathway depends on the structure of the enimine used. This divergence was not observed when the enimines were reacted with dimethyl 1,3-acetonedicarboxylate to provide bicyclo[3.3.1]nonane-3-one derivatives in excellent yields in a remarkably stereoselective reaction.     

Synthesis and antiproliferative activity of RITA and its analogs

The synthesis of RITA and a variety of five-membered heterocyclic triads by the cyclocondensation of 1,4-bis(5-substituted-2-thienyl or 2-furyl)-1,3-butadiynes with water or Na₂S·9H₂O in the presence of KOH in DMSO is described. The study on the antiproliferative activities against K562, MCF-7, A549, and HCT116 tumor cells has revealed that some of the heterocyclic triads show higher antiproliferative activities than RITA, depending on the structures of substituents, the property of heteroatoms as well as their numbers.     

Coupling Reactions of Alkynylsilanes Mediated by a Cu(I) Salt: Novel Syntheses of Conjugate Diynes and Disubstituted Ethynes

Reaction of 1-trimethylsilylalkyne with copper(I) chloride in a polar solvent, DMF, at 60 degrees C under an aerobic conditions smoothly undergoes homo-coupling to give the corresponding symmetrical 1,3-butadiynes in 70-99% yields. In addition, (arylethynyl)trimethylsilanes are found to couple with aryl triflates and chlorides in the presence of Cu(I)/Pd(0) (10 mol %/5 or 10 mol %) cocatalyst system to give the corresponding diarylethynes in 49-99% yields. The cross-coupling reaction is applied to a one-pot synthesis of the corresponding unsymmetrical diarylethynes from (trimethylsilyl)ethyne via sequential Sonogashira-Hagihara and the present cross-coupling reactions using two different aryl triflates. The reactions of (arylethynyl)trimethylsilanes with aryl(chloro)ethynes in the presence of 10 mol % of CuCl also yield the corresponding unsymmetrical 1,3-butadiynes in 43-97% yields.     

Regio- and stereoselective microwave-assisted synthesis of 5-alkyl-4-alkenyl-4-phenyl-1,3-oxazolidin-2-ones

Chiral symmetrical alk-2-yne-1,4-diols have been stereoselectively transformed into 5-alkyl-4-alkenyl-4-phenyl-1,3-oxazolidin-2-ones, which are precursors of quaternary α-amino β-hydroxy acids. The key step was the cyclization of the bis(tosylcarbamates) of 2-phenylalk-2-yne-1,4-diols, easily obtained from the starting chiral diols. These cyclizations were accomplished with complete regioselectivity and up to 92:8 dr in the presence of catalytic amounts of Ni(0) or Pd (II) derivatives under microwave heating.     

Quantum-Chemical Study of Electronic Structure and Reactivity of Diphospha-1,3-Butadienes

Abstract

Quantum-chemical calculations of the electronic structure of 1,3-, 1,4- and 2,3-diphospha-1,3-butadienes (DPB) and their derivatives with different substituents were performed. The MNDO method was used to describe the electronic structure of phosphaalkenes. The frontier orbitals of all unsubstituted DPB are of π-type. The highest occupied molecular orbital (HOMO) is delocalized through both double phosphorus-carbon bonds; the next occupied MO is a combination of two phosphorus lone pairs (n-MO). The HOMO of 2,3-DPB differs markedly from those of 1,3- and 1,4-isomers: the contributions of phosphorus and carbon p-orbitals are nearly equal, and the energy gap between HOMO and n-MO is very small (0.008 eV). The introduction of the electron-withdrawing substituents results in the reverse order of these MO's. In contrast with 1,3- and 1,4-isomers, the double bonds of 2,3-DPB are almost non-polar. Effect of substituents upon the electron density distribution are considered. The results indicate that orbitally controlled 1,4-additions should be characteristic for the derivatives of 1,3- and 1,4-DPB, similar to 1,3-butadiene. In case of 2,3-DPB, tendency to 1,4-addition should be lower; for its derivatives the reaction type depends greatly upon the electronic effects of substituents. In particular, reactions involving phosphorus lone pairs should be typical for the derivatives of 2,3-DPB with electron-withdrawing substituents.     

α-Amino acid-assisted autoxidation of naphthalene proton sponge affording 1,4-naphthoquinone nitrogen derivatives

1,8-Bis(dimethylamino)naphthalene (naphthalene proton sponge) equipped at position 4 with N-terminal α-amino acid residues undergoes unprecedented easy autoxidation in basic medium forming 5-dimethylamino-1,4-naphthoquinone along with minor amounts of its derivatives. The new reaction is of interest against the background of wide distribution of 1,4-naphthoquinones in nature, their high biological significance and extremely limited information on nitrogen compounds of this series.     

Two types of rhodium-catalyzed CS/CS metathesis reactions: formation of CS/CS bonds and CC/SS bonds

A rhodium complex catalyzes two types of single bond metathesis reactions of two CS bonds depending on the added ligand: CS/CS to CS/CS metathesis and CS/CS to CC/SS metathesis. In the presence of a catalytic amount of RhH(PPh₃)₄ and 1,1′-bis(diphenylphosphino)ferrocene (dppf), two 1-alkylthioalkynes exchange alkylthio groups to give equilibrium mixtures of four 1-alkylthioalkynes. When tris(p-methoxyphenyl)phosphine or diphenylmethylphosphine is used, 1,3-butadiynes are obtained.     

Lewis acid-catalyzed [4 + 2] benzannulation between enynal units and enols or enol ethers: novel synthetic tools for polysubstituted aromatic compounds including indole and benzofuran derivatives

The reaction of enynals 1, including o-(alkynyl)benzaldehydes, and carbonyl compounds 2, such as aldehydes and ketones, in the presence of a catalytic amount of AuBr3 in 1,4-dioxane at 100 degrees C gave the functionalized aromatic compounds 3 in high yields. Similarly, the AuBr3-catalyzed reactions of 1 with acetal compounds 5 afforded the corresponding aromatic compounds 3 in good yields. On the other hand, when the reaction was carried out in the presence of a catalytic amount of Cu(NTf2)2 and 1 equiv of H2O in (CH2Cl)2 at 100 degrees C, the decarbonylated naphthalene products 4 were obtained selectively over 3. Benzofused heteroaromatic compounds, such as indole derivatives 13 and benzofuran derivatives 15, were also synthesized by using the present benzannulation methodology.     

无溶剂超声辐射下硝酸镱高效催化合成 1,4-二氢吡啶衍生物

在Yb(NO₃)₃催化下, 芳香醛、 5,5-二甲基-1,3-环己二酮、 乙酰乙酸乙酯和醋酸铵在室温无溶剂条件下经超声辐射一锅法合成了一系列1,4-二氢吡啶衍生物, 反应时间为15~35 min, 产率为86%~97%. 该方法具有条件温和、 反应时间短且产率高的优点. 催化剂Yb(NO₃)₃对环境友好且可循环使用, 为此类化合物的合成提供了一种有效的新方法.