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Optically active [7]helicene-fused oxanorbornene polymers poly-1were synthesized by ring-opening-metathesis polymerization (ROMP) of monomer 2, which was easily accessed by [4 + 2] cycloaddition of in situ-generated [7]helicenyl aryne and furan. The optical resolution of rac-2using a chiral stationary phase afforded optically active (P)-2and (M)-2. Of the various Grubbs catalysts tested, the first-generation one was found to be optimal for this ROMP. The chiroptical properties of the polymers were studied using circular dichroism and circularly polarized luminescence.

Catalytic enantioselective 1,2-addition reactions of arylboronic acids with 1,2,5-thiadiazoline 1,1-dioxide derivatives were achieved using planar-chiral phosphine-olefin ligand L5with a bis[(2,3,4,5,6-pentafluoro)phenyl]phosphino group, showing ≤98% ee. The enantioselectivities of the addition products were improved by increasing the number of fluoro substituents on the aromatic ring of the ligand. X-ray crystallographic studies of 3aaand [RhCl/L5]2revealed the absolute configuration of the enantioenriched addition product 3and the mode of phosphine-olefin bidentate coordination of L5to a rhodium(I) cation.

Helicenes are attractive non-planar polycyclic aromatic hydrocarbons with unique optical and electronic properties. In recent years, the chemistry of “multiple helicenes” with plural helicities in a single molecule has also grown rapidly as a research area due to intriguing properties such as highly distorted structures, multidimensional intermolecular interactions, and enhanced chiroptical properties. In this review, we summarize the synthesis and the molecular structures of multiple helicenes. Taking into consideration that the applied p-conjugated framework largely affects their synthesis, molecular structures, and physical properties, we categorize them according to the central p-conjugated core from smaller to larger aromatic rings and not the criterion of the original classification of multiple helicenes (multiplicity and the number of fused rings). Furthermore, we cover structural parameters and aromaticity of multiple helicenes, especially for the individual benzene rings, based on the definition of “twisting angle” and NICS values, respectively.The chemistry of “multiple helicenes” with plural helicities in a single molecule has grown rapidly in recent years. This review focuses on the synthesis and the molecular structures of multiple helicenes, which are categorized by the central p-conjugated core from smaller to larger aromatic rings. Furthermore, the structural parameters and aromaticity of multiple helicenes, especially for the individual benzene rings, are also covered.

The gold(I)‐catalyzed intramolecular hydroarylation of o‐ethynylarylphosphonium salt 1gave phosphepinium 2or phosphinium salt 3. The use of methylphosphonium salt instead of phosphine chalcogenide is key to success for the intramolecular hydroarylation. The substrate with 2‐methoxyphenyl group at the alkyne position preferentially provided seven‐membered phosphacycle 2, while that with a hydrogen did six‐membered phosphacycle 3. Theoretical calculations revealed that the activation energy of 6‐exo‐dig cyclization in the substrate with the aryl group increased due to the steric repulsion of the two aryl rings. Furthermore, the Wittig‐type reaction of phosphepinium salt 2 aafforded methyl‐substituted phosphepin oxide 4 avia the elimination of an aryl group. A gold(I)‐catalyzed intramolecular hydroarylation reaction ofo–ethynylarylphosphine derivativeshas been investigated. The use of phosphonium salt is essential for the formation of phosphacycles, and 7‐endo‐dig and/or 6‐exo‐dig cyclized products were obtained, depending on the substrates. The effect of the substituent on the alkyne for the cyclization was also investigated by theoretical calculations.

Optically active triple helicenes (TH-1) were prepared via a palladium-catalyzed enantioselective cross-cyclotrimerization of two helicenyl arynes 5, which are generated in situfrom 3, with dialkyl acetylenedicarboxylate 4. Enantiomeric ratios of up to 98:2 were obtained when using 4aand (S)-QUINAP as the alkyne and chiral ligand, respectively. The absolute stereochemistry of TH-1awas revealed to be (M,P,M) by a single-crystal X-ray diffraction analysis. Kinetic studies of the racemization of enantiomerically pure TH-1aat elevated temperatures were conducted based on a high-performance liquid chromatography analysis. The activation energy for the racemization was found to be 29.1 kcal mol–1. Density functional theory calculations revealed that the palladium-catalyzed enantioselective cross-cyclotrimerization reactions proceed via the dynamic kinetic resolution of a five-membered palladacycle 6awith two [5]helicenes. Several initially formed stereoisomers of 6aeventually isomerize into the most thermodynamically stable palladacycle intermediate (M,P,M)-6aby inversion of the [5]helicenyl moiety. Then, the insertion of 4into 6ato form (M,P,M)-12a, followed by a reductive elimination, leads to the formation of (M,P,M)-TH-1ain a stereoselective manner. The optical properties of TH-1awere studied by circular dichroism and circularly polarized luminescence.

The reaction mechanisms of the plausible reaction process for the synthesis of hexapole helicene via a palladium-catalyzed [2 + 2 + 2] cyclotrimerization of [5]helicenyl aryne were examined using a theoretical approach. In a previous experimental study, this reaction selectively produced C2-symmetrical hexapole helicene, even though the D3-symmetrical structure is thermodynamically more stable. To clarify the mechanism underlying this reaction, density functional theory (DFT) and transition-state-theory calculations were used to evaluate the reaction profile and kinetic rate constants of the primary reactions. The thus obtained results suggest that the first step of the [2 + 2 + 2] cyclotrimerization is not a Diels–Alder reaction but an insertion of the helicenyl aryne into a metallacyclopentadiene. Subsequently, we clarified that the formation of the D3-symmetrical product is precluded by the high free-energy barrier of this reaction, while the C2-symmetrical product can be obtained at 300 K. Simulations of the time evolution of the molar fractions of the isomers were carried out based on the evaluated kinetic rate constants. The experimental result that the C2-symmetrical product is formed predominantly at 300 K was successfully reproduced in the simulations, while the isomerization into the more stable D3hexapole helicene structure is predicted to occur at 400 K.

A gold(I) complex with a 1,1′-binaphthyl-substituted diphosphene was synthesized and fully characterized. A phosphorus atom with a less-hindered binaphthyl group coordinates to a gold(I) moiety in an η1fashion. Both experiment and theoretical calculations supported the facile rotation around the C(Naph)–P bond in neutral and cationic diphosphene–gold(I) complexes. The newly obtained complex 2was applied to the intramolecular hydroarylation of aryl propynyl ethers 5, and 2H-chromenes 6were formed in 83–94% yield. Furthermore, the chiral diphosphene–gold(I) complex (S)-2was used in the atropselective reaction to furnish 6b,cwith up to 9% ee, which is the first example of the use of a diphosphene as a ligand for the transition-metal-catalyzed organic transformation.

Enantioselective desymmetrization of Cs-symmetric (η5-2,5-dialkenylphospholyl)(allyldiphenylphosphine)manganese(I) dicarbonyl complexes 1was realized by molybdenum-catalyzed asymmetric ring-closing metathesis (ARCM), and the corresponding bridged planar-chiral phosphacymantrene derivatives 2were obtained in good yields with excellent enantioselectivity. The enantioselectivity of the ARCM reaction was strongly influenced by the structures of the phospholyl-bound alkenyl groups, and the highest enantioselectivity of up to 99% ee was achieved in the reaction of 1d,e, which possess the 2-methylpropenyl substituents at the 2- and 5-positions of the η5-phospholides. Single-enantiomeric planar-chiral 2d, which was obtained by the recrystallization of the highly enantiomerically enriched ARCM product, can serve as a chiral ligand for the palladium-catalyzed asymmetric allylic alkylation to show good enantioselectivity in up to 74% ee.

Hexapole helicenes 1, which contain six [5]helicene substructures, were synthesized by Pd-catalyzed [2+2+2]cycloadditions of aryne precursor 6. Among the possible 20 stereoisomers, which include ten pairs of enantiomers, HH-1was obtained selectively. Density functional theory (DFT) calculations identified HH-1as the second most stable isomer that quantitatively isomerizes under thermal conditions into the most stable isomer (HH-2). Both enantiomers of HH-2can be separated by chiral HPLC. Single-crystal X-ray diffraction analyses revealed a saddle-like structure for (P,M,P,P,M,P) HH-1and a propeller-like structure for (P,M,P,M,P,M) HH-2. Because of the helical assembly and the resulting steric repulsion, the structure of HH-1is significantly distorted and exhibits the largest twisting angle reported so far (up to 35.7° per benzene unit). Electrochemical studies and DFT calculations indicated a narrow HOMO–LUMO gap on account of the extended π-system. Kinetic studies of the isomerization from HH-1to HH-2and the racemization of enantiomerically pure HH-2were conducted based on 1H NMR spectroscopy, HPLC analysis, and DFT calculations.

A series of substituted [4] and [5]helicenes were synthesized in moderate to good yields by an Ir-catalyzed annulative coupling of biarylcarboxylic acid chlorides with internal alkynes, which involves facile C-H bond cleavage and decarbonylation. The double annulative coupling of 1,1':5',1''-ternaphthalene-2,2''-dicarboxylic acid dichloride with 4-octyne was also accomplished to give rise to an S-shaped double helicene. Unexpectedly, a p-extended benzofluoranthene-merged [5]helicene was constructed through the annulative coupling and the successive C(aryl)-C(aryl) bond forming reaction when 1,1':4',1''-ternaphthalene-2,2''-dicarboxylic acid dichloride was employed as the substrate. The crystal structure and the optical properties of the latter unique product were also investigated.A series of substituted [4] and [5]helicenes were synthesized in moderate to good yields by an Ir-catalyzed annulative coupling of biarylcarboxylic acid chlorides with internal alkynes, which involves facile C-H bond cleavage and decarbonylation. Furthermore, S-shaped helicene and p-extended benzofluoranthene-merged [5]helicene were also accessible by a similar protocol.

Molybdenum‐catalyzedasymmetric ring‐closing metathesis has been used for the kinetic resolution of racemic planar‐chiral (η6‐arene)chromium complexes with excellent enantioselectivity. The products are excellent precursors for the synthesis of various planar‐chiral (η6‐arene)chromium derivatives and can also be applied as chiral ligands in rhodium‐catalyzed asymmetric reactions.

Die kinetische Racematspaltungplanar‐chiraler (η6‐Aren)chrom‐Komplexe gelingt durch eine molybdänkatalysierte asymmetrische Ringschlussmetathese. Die hoch enantiomerenreinen Produkte sind ausgezeichnete Synthesevorstufen für planar‐chirale (η6‐Aren)chrom‐Derivate; außerdem eignen sie sich als chirale Liganden in rhodiumkatalysierten asymmetrischen Reaktionen.

Methylenecyclopentanones were synthesized by the nickel-catalyzed 311 cycloaddition reactions of alkenyl Fischer carbene complexes with methylenecyclopropanes. The methylenecyclopropane was transformed into the C2-symmetric bis-cyclopentapyridazine derivative by reacting withp-toluenesulfonyl hydrazine.

N-Aryl indoles with axially chiral N−C bonds were synthesized by stereoselective nucleophilic aromatic substitution reactions of planar chiral arene chromium complexes. Stereoselective chromium tricarbonyl migration was achieved in the sterically hindered N-aryl indole chromium complex by refluxing in toluene.

The new dithiolate-bridged Ru−Rh heterobimetallic dihydride complex [Cp*Rh(μ2-1,2-S2C6H4)(μ2-H)RuH(PPh3)2] (2) has been prepared, and its reactions with CO and alkynes have been studied. Treatment of the rhodium 1,2-benzenedithiolate complex [Cp*Rh(1,2-S2C6H4)] (Cp* = η5. 5BJ5) with [RuHCl(PPh3)3] in THF produces the hydride- and dithiolate-bridged Ru−Rh heterobimetallic complex [Cp*Rh(μ2-1,2-S2C6H4)(μ2-H)RuCl(PPh3)2] (1), which was further converted to the dihydride complex [Cp*Rh(μ2-1,2-S2C6H4)(μ2-H)RuH(PPh3)2] (2) upon treatment with KOH/i-PrOH. Complex 2 reacts with CO to give the dicarbonyl complex [Cp*Rh(μ2-1,2-S2C6H4)Ru(CO)2(PPh3)] (3). Reaction of 2 with p-tolylacetylene (2 equiv) proceeds with hydrogenation of the alkyne and subsequent oxidative addition of the sp C−H bond to give the alkynyl hydride complex [Cp*Rh(μ2-1,2-S2C6H4)(μ2-H)Ru(C&tbd1;CTol-p)(PPh3)2] (4a). The analogous alkynyl hydride complex [Cp*Rh(μ2-1,2-S2C6H4)(μ2-H)Ru(C&tbd1;CSiMe3)(PPh3)2] (6 ) has also been prepared. Complex 4a reacts with excess p-tolylacetylene to produce the ruthenacyclopentadiene complex [Cp*Rh{μ2-η2:η4-1,3-(p-Tol)2C4H2}Ru(S2C6H4)(PPh3)] (5), whereas similar treatment of 4a with excess diphenylacetylene induces 1:2 coupling of the two different alkynes to form the η6-arene complex [Cp*Rh(μ2-1,2-S2C6H4)Ru{η6. 6SK4H(p-MeC6H4)}] (6). Reaction of 4a with CO proceeds with dissociation of one of the Ru−S bonds and with retention of the alkynyl hydride structure to give the CO adduct [Cp*Rh(μ2-1,2-S2C6H4)(μ2-H)Ru(C&tbd1;CTol-p)(CO)(PPh3)2] (7). The structures of 1, 3, 6 , and 5−7 have been determined by X-ray crystallography.

Diastereomerically axial naphthyl(η6-phenyl)Cr(CO)3complexes were prepared by cross-coupling of (arene)chromium complexes with naphthylboronic acids and subsequent axial isomerization by refluxing of the coupling products in a higher boiling point solvent.

Nucleophilic substitution of tricarbonyl(2,4,6-trimethylphenyl 2-methoxybenzoate)-chromium complexes with aryl Grignard reagents affords stereoselectively axially chiral biaryls.

The diruthenium μ2-imido μ2-methylene complex [(Cp*Ru)2(μ2-NPh)(μ2-CH2)] serves as a bifunctional scaffold for cluster synthesis, producing a μ3-imido Ru2Pt cluster [(Cp*Ru)2(μ3-NPh)(μ2-CH2)Pt(PMe3)2] on treatment with [Pt(η2-C2H4)(PMe3)2] and a μ3-methylidyne Ru4Pd2cluster [(Cp*Ru)2(μ2-NPh)(μ3-CH)PdCl]2with [PdMeCl(cod)].

syn-Biaryl chromium complexes having a coordinating ortho-substituent gave anti-biaryl chromium complexes 5 with an inversion of the planar chirality by heating in a non-aromatic solvent.

Axially chiral N—C bonds are obtained in products (II) by diastereoselective migration of Cr(CO)3from the benzene ring in (I) to the acridane or phenoxazine system in (II).

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

For Abstract see ChemInform Abstract in Full Text.

For Abstract see ChemInform Abstract in Full Text.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.