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Toward a conversion of aldehydes into arenes, we designed a sequence involving the initial reaction of an aldehyde to give a fulvene, followed by photochemical and platinum‐catalyzed rearrangements into a Dewar benzene derivative, which finally isomerizes into the targeted arene. While computational studies support the plausibility of this route, we found that fulvene irradiation resulted in an unexpected isomerization into a spiro[2.4]heptadiene. This unusual photorearrangement has been investigated mechanistically and provides access to a variety of spiro[2.4]heptadienes with different substituents. [ABSTRACT FROM AUTHOR]

Cumulenes have attracted considerable attention due to their unique structural and electronic properties. Despite their high potential for constructing condensed π‐conjugated molecules, the synthetic utility of longer cumulenes remains to be established owing to their inherently high reactivity. Conjugated bisbutatrienes having two cumulene moieties linked by a spacer as a mimic of a longer cumulene were evaluated. Here, the synthesis and characterization of hexafluorocyclopentane‐bridged bisbutatrienes are described. These bisbutatrienes underwent various cyclizations, to construct the unique π‐extended frameworks inaccessible by other methodologies. The bisbutatrienes were converted into fulvenes, pentalene, germacycle, and benzocyclobutene under various conditions. Furthermore, a cyclooctatetraene derivative was synthesized by a one‐step dimerization of the bisbutatriene. [ABSTRACT FROM AUTHOR]

We report di- and trinuclear palladium sandwich complexes of cross-π-conjugated fulvenes. Structural and theoretical analysis revealed that a fulvene sandwich framework holds a metal–metal bonded moiety, where the dinuclear and trinuclear bonds feature strong donation and back-donation, respectively. The trinuclear fulvene sandwich complex undergoes a unique reversible extrusion of a Pd atom from inside to outside the sandwich framework. [ABSTRACT FROM AUTHOR]

An efficient [4+2] cycloaddition reaction of fulvenes with aza-o-quinone methides, generated in situ from N -(o -chloromethyl)aryl sulfonamides with the assistance of a base, has been developed to afford a series of tetrahydroquinoline derivatives. The reaction tolerates a wide range of aza- o -quinone methides and fulvenes bearing four- to seven-membered rings to afford the corresponding tetrahydroquinolines in moderate to good yields. Based on a literature analysis, a plausible mechanism for this [4+2] cycloaddition is proposed. [ABSTRACT FROM AUTHOR]

1,3-Cyclopentadienes, fulvenes and their derivatives regio- and stereoselectively react with the in situ generated dichloroketene to form the corresponding bicycles of the [3.2.0]heptane topology. The latter are transformed into block synthons with a higher synthetic potential, including chiral ones. A number of examples are used to demonstrate the possibility of their use in the targeted synthesis of bioactive cyclopentanoids. [ABSTRACT FROM AUTHOR]

Organocatalytic enantioselective 1,3‐dipolar [6+4] cycloadditions of pyrylium ion intermediates with fulvenes promoted by a chiral primary amine catalyst have been developed to proceed in moderate to good yields and high enantioselectivities. The resultant chiral bicyclo[6.3.0]undecane scaffold containing a transannular bridging ether is densely functionalised providing a rigid scaffold for further manipulations. Computational studies give important insights into the role of the primary amine catalyst. Analysis of the reaction shows that the catalytic reaction proceeds in a step‐wise manner and rationalises the stereochemical outcome of the reaction. Several stereoselective complexity‐generating transformations, facilitated by the diverse functional groups and transannular bridge, are presented, highlighting the versatility of the core towards a number of the cyclooctanoid natural products. [ABSTRACT FROM AUTHOR]

Huisgen's 1960 announcement of the concept of 1,3‐dipolar cycloadditions was published the year before Alder's study of the reaction of diazomethane and dimethylfulvene. The diazomethane reaction was studied again in 1970 by Houk et al. and shown to give a [6+4] adduct. Padwa's nitrile ylide cycloaddition to dimethylfulvene (1978) gave [6+4] and [4+2] adducts. We performed computational studies of these reactions with density functional theory (DFT) and show that they involve ambimodal [6+4]/[4+2] transition states that can lead to either type of cycloadduct from one transition state. We dedicate this paper to the extraordinary life and humanity of Rolf Huisgen, and to the undying influence of his discoveries on chemistry. [ABSTRACT FROM AUTHOR]

Huisgen's 1960 announcement of the concept of 1,3‐dipolar cycloadditions was published the year before Alder's study of the reaction of diazomethane and dimethylfulvene. The diazomethane reaction was studied again in 1970 by Houk et al. and shown to give a [6+4] adduct. Padwa's nitrile ylide cycloaddition to dimethylfulvene (1978) gave [6+4] and [4+2] adducts. We performed computational studies of these reactions with density functional theory (DFT) and show that they involve ambimodal [6+4]/[4+2] transition states that can lead to either type of cycloadduct from one transition state. We dedicate this paper to the extraordinary life and humanity of Rolf Huisgen, and to the undying influence of his discoveries on chemistry. [ABSTRACT FROM AUTHOR]

Gold‐catalyzed cyclization of 1,5‐diynes with ketones as reagents and solvent provides diversely substituted vinyl ethers under mild conditions. The regioselectivity of such gold‐catalyzed cyclizations is usually controlled by the scaffold of the diyne. Herein, we report the first solvent‐controlled switching of regioselectivity from a 6‐endo‐dig‐ to 5‐endo‐dig‐cyclization in these transformations, providing fulvene derivatives. With respect to the functional‐group tolerance, aryl fluorides, chlorides, bromides, and ethers are tolerated. Furthermore, the mechanism and selectivity are put to scrutiny by experimental studies and a thermodynamic analysis of the product. Additionally, 6‐(vinyloxy)fulvenes are a hitherto unknown class of compounds. Their reactivity is briefly evaluated, to give insights into their potential applications. [ABSTRACT FROM AUTHOR]

A new facet of nucleophilic fulvene epoxidations has been uncovered. 6‐Arylfulvenes containing an ortho or para hydroxyl group react with basic hydrogen peroxide in an unusual manner; the epoxidation of the fulvene exocyclic double bond is followed by a phenoxide ion‐initiated epoxide ring opening to form an o‐quinone methide (o‐QM) intermediate. The resulting cyclopentadienolate undergoes an unusual oxy‐anion accelerated [1,5]‐sigmatropic o‐QM shift. Computational studies reveal that the activation energy for the [1,5]‐QM‐shift in the cyclopentadienolate intermediate is quite low, signifying the acceleration caused by the oxy‐anion group. Placement of a second hydroxyl group in the 6‐aryl ring at C5 epoxidation via electron donation to the o‐QM carbon; instead, an intramolecular oxa‐6‐π‐electrocyclization of the o‐QM intermediate onto the cyclopentadiene is observed. [ABSTRACT FROM AUTHOR]

A divergent approach toward the protecting‐group‐free total synthesis of oxidized benzofulvene sesquiterpenoids is described. Highlight of our synthesis includes regio‐ and stereoselective assembly of the common intermediate 9 by the orchestrated application of a Pd(0)‐catalyzed reductive dehalogenation, a solvent‐free methylenation, and a vinylogous Stork enamine aldol condensation in a substrate‐controlled manner. The advanced intermediate 9 was efficiently transformed to nicotianasesterpenes A, B, and a polygonum sesquiterpenoid, respectively. [ABSTRACT FROM AUTHOR]

The synthesis and crystal structures of a series of 6-aryl­fuvlenes (fulvene is 5-methyl­idene­cyclo­penta-1,3-diene) with varying methyl­ation patterns on the 6-phenyl substituent are reported, namely 6-(3-methyl­phen­yl)-1,3-di­phenyl­fulvene (C25H20), 6-(4-methyl­phen­yl)-1,3-di­phenyl­fulvene (C25H20), 6-mesityl-3-di­phenyl­fulvene (C27H24) and 6-(2,3,4,5,6-penta­methyl­phen­yl)-1,3-di­phenyl­fulvene (C29H28). The bond lengths are typical of those observed in related fulvenes. A network of C—H· · ·π ring inter­actions consolidates the packing in each structure. [ABSTRACT FROM AUTHOR]

Due to the reversal in electron counts for aromaticity and antiaromaticity in the closed‐shell singlet state (normally ground state, S0) and lowest ππ* triplet state (T1 or T0), as given by Hückel's and Baird's rules, respectively, fulvenes are influenced by their substituents in the opposite manner in the T1 and S0 states. This effect is caused by a reversal in the dipole moment when going from S0 to T1 as fulvenes adapt to the difference in electron counts for aromaticity in various states; they are aromatic chameleons. Thus, a substituent pattern that enhances (reduces) fulvene aromaticity in S0 reduces (enhances) aromaticity in T1, allowing for rationalizations of the triplet state energies (ET) of substituted fulvenes. Through quantum chemical calculations, we now assess which substituents and which positions on the pentafulvene core are the most powerful for designing compounds with low or inverted ET. As a means to increase the π‐electron withdrawing capacity of cyano groups, we found that protonation at the cyano N atoms of 6,6‐dicyanopentafulvenes can be a route to on‐demand formation of a fulvenium dication with a triplet ground state (T0). The five‐membered ring of this species is markedly Baird‐aromatic, although less than the cyclopentadienyl cation known to have a Baird‐aromatic T0 state. [ABSTRACT FROM AUTHOR]

Gold(I) chloride complexes of arylisocyanides derived from 9‐benzylidene‐9H‐fluorene (Flu), 5‐benzylidene‐1,2,3,4‐tetraphenylcyclopentadiene (TPCp), and 5‐benzylidene‐5H‐dibenzo[a,d]cycloheptene (Dbs) have been prepared. The crystal structures and electronic properties of the three complexes are discussed. UV/Vis data complemented by DFT calculations indicate that the gold(I) centers act as Lewis acids and increase the acceptor strength of the isocyano group. The metal center therefore indirectly affects the optical properties of the π‐conjugated ligands, but is not directly involved in electronic transitions. Gold(I) complexes of phenylisocyanides equipped with fulvenyl groups have been prepared and characterized. These compounds represent a new class of isocyanide complexes featuring a conjugated, redox‐active chromophore. [ABSTRACT FROM AUTHOR]

Abstract: The first peri‐ and stereoselective [10+4] cycloaddition between catalytically generated amino isobenzofulvenes and electron‐deficient dienes is described. The highly stereoselective catalytic [10+4] cycloaddition exhibits a broad scope with high yields, reflecting a robust higher‐order cycloaddition. Experimental and computational investigations support a kinetic distribution of intermediate rotamers dictating the enantioselectivity, which relies heavily on additive effects. [ABSTRACT FROM AUTHOR]

The reaction of Et3Al/CH2I2 reagent with cyclopropanated spiro[2.4]hepta-4,6-diene and 6-substituted fulvenes in CH2Cl2 was found to lead to the selective formation of rearrangement products through sequential cyclopropyl-allyl rearrangement and cyclopropanation. [ABSTRACT FROM AUTHOR]

The mechanism of cycloaddition reactions for 6-dimethylaminofulvene and 6,6-diphenylfulvene with tetrazine and diazacyclopentadienone are studied by DFT at the MPWB1K/cc-pVDZ level of theory. The energy results indicated that the [6 + 4] cycloaddition reaction of 6-dimethylaminofulvene with tetrazine and diazacyclopentadienone derivatives proceeds in a stepwise fashion, while the [2 + 4] cycloaddition reaction of 6,6-diphenylfulvene might proceed in a one-step fashion. Our calculations showed some unfavorable processes with unstable cycloadducts arising from [4 + 2] cycloaddition reactions which are unobserved in the experimental results. Also, an analysis of the Parr functions for the reactants allows us to provide an explanation of the selectivity of these cycloaddition reactions. [ABSTRACT FROM AUTHOR]

Abstract: Highly enantioselective [8+3] high‐order cycloaddition reactions of tropones or azaheptafulvenes with meso‐aziridines were achieved by a desymmetrization/annulation process in the presence of chiral N,N′‐dioxide/Mg(OTf)2 complex. The corresponding tetrahydrocyclohepta[b][1,4]oxazines and tetrahydro‐1H‐cyclohepta‐ [b]‐pyrazines were obtained in good yields (66–98 %) with excellent diastereo‐ and enantioselectivities (>19:1 d.r., 90–96 % ee). A possible transition state model was proposed to elucidate the origin of chiral induction based on the control experiments and X‐ray crystal structure of the catalyst. [ABSTRACT FROM AUTHOR]

Abstract: 6,6‐Dicyanopentafulvene derivatives and metallocenes with redox potentials appropriate for forming their radical anions form highly persistent donor–acceptor salts. The charge‐transfer salts of 2,3,4,5‐tetraphenyl‐6,6‐dicyanofulvene with cobaltocene (1⋅Cp2Co) and 2,3,4,5‐tetrakis(triisopropylsilyl)‐6,6‐dicyanofulvene with decamethylferrocene (2⋅Fc*) have been prepared. The X‐ray structures of the two salts, formed as black plates, were obtained and are discussed herein. Compared with neutral dicyanopentafulvenes, the chromophores in the metallocene salts show substantial changes in bond lengths and torsional angles in the solid state. EPR, NMR, and optical spectroscopy, as well as superconducting quantum interference device (SQUID) measurements, reveal that charge‐separation in the crystalline states and in frozen and fluid solutions depends on subtle differences of redox potentials, geometry, and on ion pairing. Whereas 1⋅Cp2Co reveals paramagnetic character in the crystalline state and in solution, compound 2⋅Fc* shows a delicate balance between para‐ and diamagnetism, depending on the temperature and solvent characteristics. [ABSTRACT FROM AUTHOR]

The synthesis and structural properties of a series of chromium tricarbonyl 'piano-stool' complexes bearing substituted pentafulvene ligands were studied. The complexes, tricarbonyl(1,3,6-triphenylfulvene)chromium(0) benzene hemisolvate, [Cr(C24H18)(CO)3]·0.5C6H6 (I), tricarbonyl[1,3-diphenyl-6-(3-vinylphenyl)fulvene]chromium(0), [Cr(C26H20)(CO)3] (II), and tricarbonyl[1,3-diphenyl-6-(pyren-1-yl)fulvene]chromium(0), [Cr(C34H22)(CO)3] (III), each have a distorted octahedral geometry, with the fulvene coordinated in a ⍤-η²:⍤-η²:⍤-η² fashion. Significant deviation of the exocyclic fulvene double bond from the cyclopentadiene plane accompanies coordination. Evidence of non-covalent ⍤-⍤ interactions was observed in both (I) and (III), with centroid-to-centroid distances ranging from 3.330(8) to 3.494(8)Å. [ABSTRACT FROM AUTHOR]

Abstract: Donor–donor′–acceptor triads (1, 2), based on [3.3]paracyclophane ([3.3]PCP) as a bridge, with electron‐donating properties (D′) using 1,4‐dithiafulvene (DTF; TTF half unit) as a donor and dicyanomethylene (DCM; TCNE half unit) or an ethoxycarbonyl‐cyanomethylene (ECM) as an acceptor were designed and synthesized. The pulse radiolysis study of 1 a in 1,2‐dichloroethane allowed the clear assignment of the absorption bands of the DTF radical cation (1 a.+), whereas the absorption bands due to the DCM radical anion could not be observed by γ‐ray radiolysis in 2‐methyltetrahydrofuran rigid glass at 77 K. Electrochemical oxidation of 1 a first generates the DTF radical cation (1 a.+), the absorption bands of which are in agreement with those observed by a pulse radiolysis study, followed by dication (1 a2+). The ESR spectrum of 1 a.+ showed a symmetrical signal with fine structure and an ESR simulation predicted that the spin of 1 a.+ is delocalized over S and C atoms of the DTF moiety and the central C atom of the trimethylene bridge bearing the DTF moiety. Pulse radiolysis, ESR, and electrochemical studies indicate that the DTF radical cation of 1 a.+ is more stable than that of 6.+, and the latter shows a strong tendency to dimerize. This result indicates that the [3.3]PCP moiety as a bridge can stabilize the DTF radical cation more than the 1,3‐diphenylpropane moiety because of kinetic stability due to its rigid structure and the weak electronic interaction of DTF and DCM moieties through [3.3]PCP. [ABSTRACT FROM AUTHOR]

The influence of mono‐ and multiple substituent effect on the reduction potential (E0) of 1,3,6‐triphenyl fulvenes is investigated using B3LYP‐SMD/6‐311+G(d,p) level density functional theory. The molecular electrostatic potential (MESP) minimum at the fulvene π‐system (Vmin) and the change in MESP at any of the fulvene carbon atoms (ΔVC) for both neutral and reduced forms are used as excellent measures of substituent effect from the para and meta positions of the 1,3 and 6‐phenyl moieties. Substitution at 6‐phenyl para position has led to significant change in E0 than any other positions. By applying the additivity rule of substituent effects, an equation in ΔVC is derived to predict E0 for multiply substituted fulvenes. Further, E0 is predicted for a set of 2000 hexa‐substituted fulvene derivatives where the substituents and their positions in the system are chosen in a random way. The calculated E0 agreed very well with the experimental E0 reported by Godman et al. Predicting E0 solely by substituent effect offers a simple and powerful way to select suitable combinations of substituents on fulvene system for light harvesting applications. © 2018 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Abstract: Molecules comprised of three covalently linked bi‐stable switches can exist in states described by a combination of binary numbers, one for each individual switch: ⟨000⟩, ⟨001⟩, etc. Here we have linked three photo‐/thermoswitches together in a rigid macrocyclic structure, one azobenzene (bit no 1) and two dihydroazulenes (DHAs; bits no 2 and 3) and demonstrate how electronic interactions and unfavorable strain in some states can be used to control the speed by which a certain state is reached. More specifically, upon irradiation of state ⟨000⟩, the AZB isomerizes from trans to cis and the two DHAs to vinylheptafulvenes (VHFs), generating ⟨111⟩. The thermal VHF‐to‐DHA back‐reactions from this state also occur stepwise and can be accelerated by photo‐induced AZB cis‐to‐trans conversion, proceeding via ⟨011⟩ to ultimately furnish ⟨000⟩. Overall, the accessibility to a specific state of one bit was found to depend on the states of its neighboring bits. [ABSTRACT FROM AUTHOR]

An unprecedented copper(i)-catalyzed asymmetric inverse electron demand Diels–Alder reaction of azoalkenes with fulvenes is reported. This methodology offers a directed entry to synthesize bicyclic tetrapyridazine derivatives in good yield with exclusive regioselectivity and excellent stereoselectivity. [ABSTRACT FROM AUTHOR]

Abstract: It has been established that reductive complexation of functionalized benzofulvenes, which are readily prepared from commercially available indene and 2‐methylindene, with RhCl3 in ethanol affords the corresponding indenyl–rhodium(III) dichlorides bearing substituents at the 1‐ (H or CO2Et), 2‐ (H or Me), and 3‐ [CH2Ph or CH2(2‐MeOC6H4)] positions. The indenyl–rhodium(III) complexes bearing one ethoxycarbonyl group showed higher thermal stability and regioselectivity than our previously reported CpERhIII complex toward the oxidative [3+2] annulation of acetanilides with internal alkynes. [ABSTRACT FROM AUTHOR]

Aluminum carbenoid Et2AlCH2I reacts with 6-substituted fulvenes to give tricyclopropanes in high yields. Calculations at the B3LYP/6-31G(d) level of theory show that coplanar arrangement of the double bonds facilitates cyclopropanation due to conjugation in the transition state. Aluminum carbenoid Et2AlCH2I was generated by either the reaction of equimolar amounts of Et3Al and CH2I2 in hexane or treatment of Et2AlI with CH2N2 in dichloromethane. [ABSTRACT FROM AUTHOR]

We report visible color changes and new intense, bathochromically shifted bands in electronic absorption spectra that reach into the near-infrared region (up to 862 nm) upon protonation of nine pentafulvene and expanded pentafulvalene derivatives. This phenomenon can only be explained by the formation of carbocations with highly delocalized charges. Solution pKa values in organic solvents were determined, making use of the method of relative basicity measurements. All seven 6-phenylpentafulvenes are weak bases, and pKa values of the protonated forms range from 0.92 to 10.29 in acetonitrile and from 1.3 to 5.9 in 1,2-dichloroethane. For 6-phenylfulvenes with varying para-substituents on the phenyl ring, pKa values correlate well with the Hammett parameters σpara. Furthermore, for most compounds, electrochemical reduction is significantly facilitated by protonation. Extensive theoretical and NMR studies strongly support the postulated protonation at carbon. [ABSTRACT FROM AUTHOR]

Abstract: The [8+2] cycloaddition of indene‐2‐carbaldehydes and nitro olefins is described to provide benzonorbornene scaffolds in a highly peri‐, diastereo‐, and enantioselective fashion in the presence of a C2‐symmetric aminocatalyst. This reaction, which proceeds through a transient semi‐aromatic amino isobenzofulvene, represents the first example of catalytic formation and transformation of these species. Quantum chemical calculations suggest a kinetically controlled stepwise mechanism where the stereochemistry is determined in the first bond‐forming event. Beyond the useful [8+2] cycloadducts, [10+4] cycloadducts have been identified in silico as potential off‐pathway intermediates. [ABSTRACT FROM AUTHOR]

Abstract: The [8+2] cycloaddition of indene‐2‐carbaldehydes and nitro olefins is described to provide benzonorbornene scaffolds in a highly peri‐, diastereo‐, and enantioselective fashion in the presence of a C2‐symmetric aminocatalyst. This reaction, which proceeds through a transient semi‐aromatic amino isobenzofulvene, represents the first example of catalytic formation and transformation of these species. Quantum chemical calculations suggest a kinetically controlled stepwise mechanism where the stereochemistry is determined in the first bond‐forming event. Beyond the useful [8+2] cycloadducts, [10+4] cycloadducts have been identified in silico as potential off‐pathway intermediates. [ABSTRACT FROM AUTHOR]

Abstract: Azulene, acenaphthylene and fulvene derivatives exhibit important physical properties useful in materials chemistry as well as valuable biological properties. Since about two decades ago, the metal‐catalyzed functionalization of such compounds, via C−H bond activation of their 5‐membered carbocyclic ring, proved to be a very convenient method for the synthesis of a wide variety of azulene, acenaphthylene and fulvene derivatives. For such reactions, there is no need to prefunctionalize the 5‐membered carbocyclic rings. In this review, the progress in the synthesis of azulene, acenaphthylene and fulvene derivatives via metal‐catalyzed C−H bond activation of their 5‐membered carbocyclic ring are summarized. [ABSTRACT FROM AUTHOR]

Simple enantioselective synthesis of 6,6-disubstituted pentafulvenes bearing chiral pendant hydroxy groups are attained by cascade reactivity using commercially available proline-based organocatalysts. Condensation of cyclopentadiene with the acetyl function of a 1,2-formylacetophenone, followed by cyclization of a resulting fulvene-stabilized carbanion with the formyl group, generates bicyclic chiral alcohols with initial er values up to 94:6. Exceptional enantio-enrichment of the resultant alcohols results upon crystallization-even near racemic samples spontaneously de-racemize. This enables new families of substituted cyclopentadienes that are both enantiomerically and diastereomerically pure to be rapidly attained. [ABSTRACT FROM AUTHOR]

Abstract: The convenient syntheses of new organophosphorus‐substituted benzofulvenes with indenyl moieties from bis(trimethylsilyl) inden‐2‐ylphosphonate and substituted azomethines in the presence of the effective initiator‐sodium hydride are developed. The following treatment of phosphonates with methanolic sodium methylate gives stable water‐soluble disodium salts of corresponding phosphonic acids. [ABSTRACT FROM AUTHOR]

Quantum-chemical calculations by the density functional theory method at the B3LYP/6- 311++G** level have shown that the fulvene form of pentamethoxycarbonylcyclopentadiene 1 in the gas phase is more favorable in energy than cyclopentadiene form 2 by Δ E = 7.8 kcal/mol. The fluxional behavior of fulvene 1, detected by dynamic NMR can be explained by the mechanism of circular low-barrier 1,9-O,O'-H shifts accompanied by rotations of the hydroxymethoxymethylene substituent about the С=С bond with the activation barrier Δ E = 23.5 (gas) and 20.9 (CHCl) kcal/mol. This reaction path is 18.6 kcal/mol more favorable in energy than transition of fulvene 1 to cyclopentadiene 2 with subsequent 1,5- sigmatropic hydrogen shifts in the five-membered ring. [ABSTRACT FROM AUTHOR]

A Lewis acid catalyzed double hydro(hetero)arylation of alkyl-substituted pentafulvenes for the synthesis of bisindolesubstituted cyclopentenoids has been developed. The scope of the reaction was explored with a wide range of indoles and pentafulvenes, and mechanistic insights were obtained. In addition, we have also demonstrated a hydro(hetero)arylation-dehydroxylation reaction of 2-hydroxy-substituted pentafulvenes to afford bisindole derivatives with isoprenyl-substituted cyclopentene moieties. [ABSTRACT FROM AUTHOR]

An effective photo-induced β-elimination of an alcohol leading to a vinyl compound is introduced for the first time. 9-Fluorenylmethanol was irradiated in a solution using a Xe lamp and was efficiently converted to dibenzofulvene (DBF) (9-methylenefluorene) in the absence of base which is necessary in the corresponding ground-state reaction. [ABSTRACT FROM AUTHOR]

The switching behaviour of dihydroazulene/vinylheptafulvene molecule with different anchoring groups sandwiched between two zigzag-edged graphene nanoribbons (ZGNRs) electrodes is investigated by applying nonequilibrium Green's function formalism combined with first-principles density functional theory. The calculated results show that the anchoring groups play a significant role in determining the electronic transport properties and switching behaviour of the molecular junctions. A higher current switching ratio without any oscillation can be obtained for the molecular junctions with carbon atom anchoring group, which suggests that this system has a broader application in future logic and memory devices. [ABSTRACT FROM AUTHOR]

We have developed preparative methods for the synthesis of substituted fulvenes including inden-2-ylphosphonic acid fragments, as well as aromatic and heterocyclic substituents, based on bis(trimethylsilyl)inden-2-ylphosphonate and substituted azomethines in the presence of sodium hydride as an efficient initiator of the reaction. Subsequent treatment of the phosphonates with methanolic solution of sodium methoxide furnished water-soluble disodium salts of the corresponding phosphonic acids. [ABSTRACT FROM AUTHOR]

Based on the total π-electron energies Eπs of Hückel Molecular Orbital (HMO) method for all the possible isomers of conjugated acyclic polyenes (C2nH2n+2) up to n = 7, the structure-stability relation of the possible isomers was analyzed. It was shown that the mean length of conjugation L can roughly predict the ordering of stability among isomers, while the Z-index, or Hosoya-index, can almost perfectly reproduce their stability. Further, the genealogy of the conjugated acyclic polyene family was obtained by drawing systematic diagrams connecting these isomers of different n, and governed by several simple rules. Namely, the stability change of a given isomer in the genealogy connecting n and n + 1 polyenes can be classified into three different modes of vinyl addition (elongation, inner and outer branching) and horn growing, i.e., substitution of -HC=CH- moiety with -HC(=CH2)-C(=CH2)H-. By using the Z-index, we can extend this type of discussion to polyene radicals and even to "cross-conjugated" cyclic polyenes containing only one odd-membered cycle, such as radialene and fulvene. [ABSTRACT FROM AUTHOR]

Functionalization of molecular photoswitches at specific positions offers a way of tuning their switching properties. The work presented here describes the development of a new protocol towards the synthesis and functionalization of the dihydroazulene/ vinylheptafulvene (DHA/VHF) photo-/thermoswitch. The key step is a facile condensation reaction using a functionalized tropone derivative, and the new synthetic method was employed in the regioselective preparation of a novel dimethyl-substituted DHA photoswitch. This compound presents the first accessible derivative with alkyl groups on the seven-membered ring of the system — at positions C5 and C7. From experimental and theoretical kinetics studies on the thermal VHF-to-DHA electrocyclic reaction, the influence of the electron-donating methyl groups was elucidated. In addition, we subjected a small selection of 4,8a-dialkylated compounds to a computational study to elucidate how steric interactions can alter the relative DHA–VHF stabilities. The synthetic methodology offers access to novel DHA scaffolds and substitution patterns, which in turn can lead to systems that can help to address broader questions concerning the potential applicability of the DHA/VHF system in the context of solar-thermal energy- storage systems or other photochromic applications. [ABSTRACT FROM AUTHOR]

The title compound exhibits a number of modes of reactivity toward nucleophiles/bases owing to the presence of several electrophilic and potentially nucleophilic sites in the molecule. We explored the reactions of 6-(chloromethyl)-6- methylfulvene with oxygen and nitrogen nucleophiles and bases as well as a carbon-based nucleophile (an enamine) and realized all possible reactivity modes predicted on the basis of electrophilic and nucleophilic positions in this compound. [ABSTRACT FROM AUTHOR]

The development of new materials for solar-to-energy conversion should consider stability, ease of fabrication, and beneficial photophysical properties. In this context, a set of novel π-conjugated building blocks, with phospha- and arsaalkenes possessing a unique dithienyl annulated heterofulvenoid core, have been prepared as air- and moisture-stable sensitizers. These compounds unify electron-donor and -acceptor moieties, making them potential candidates for light-harvesting applications. Optical characterization of these systems was performed by steady-state and time-resolved absorption spectroscopy, supported by time-dependent DFT calculations. Tuning of the optical properties of these systems can be achieved by varying the pnictogen element at the bridgehead position, giving a bathochromic shift of ≈40 nm and coordinating the phosphaalkene towards gold AuI centers. The latter results in a ≈2000-fold extension of the ≈10 ps lifetime of uncoordinated systems well into the ns regime. [ABSTRACT FROM AUTHOR]

It has been established that a RhI+/segphos complex catalyzes the [2+2+1] cycloaddition of 1,6-diynes with cyclopropylideneacetamides to give substituted fulvenes in good yields. The reductive complexation of the product fulvenes with RhCl3 in EtOH furnished the corresponding dinuclear cyclopentadienyl RhIII complexes bearing a pendant amide moiety. These RhIII complexes were highly active catalysts for oxidative annulation and cyclization through C(sp2)−H and C(sp3)−H functionalization. [ABSTRACT FROM AUTHOR]

It has been established that a RhI+/segphos complex catalyzes the [2+2+1] cycloaddition of 1,6-diynes with cyclopropylideneacetamides to give substituted fulvenes in good yields. The reductive complexation of the product fulvenes with RhCl3 in EtOH furnished the corresponding dinuclear cyclopentadienyl RhIII complexes bearing a pendant amide moiety. These RhIII complexes were highly active catalysts for oxidative annulation and cyclization through C(sp2)−H and C(sp3)−H functionalization. [ABSTRACT FROM AUTHOR]

The geometries of triafulvene (TF) and its exocyclic Si, Ge, and Sn analogues complexes with F, Cl, Br, and I halogen atoms (TF(X)···Y, X═C, Si, Ge, and Sn; Y═F, Cl, Br, and I) were studied. The complexes were optimized at DFT(B3LYP)/6–311+G(d,p) level of theory. To assess the aromaticity of the considered complexes the geometry-based (HOMA), magnetism-based (NICS), and recently introduced electronic-based (electric field gradient (EFG(0); Shannon aromaticity (SA)) aromaticity indices were employed. The increasing tendency of aromaticity in each complex species was noted as the series of TF(X)···F > TF(X)···Cl > TF(X)···Br > TF((X)···I. Then, the binding energies corrected by basis set super position error (BSSE) were calculated by single point energy calculations at M06-2X/6-311+G(d,p) level. Natural bond orbital (NBO) analysis confirmed that the charge transfer takes place from TF(X) to the halogen atoms. Some topological parameters, within the framework of the quantum theory of atoms in molecules (QTAIM), were also calculated to estimate the aromaticity of the complexes. It was seen that there are some important correlations between the topological parameters and aromaticity indices. In addition the most striking finding was that all the TF(X) molecules are connected with the halogen atoms through Y···C1═C2 (π) noncovalent interaction. This interaction was also investigated through noncovalent interaction (NCI) analysis. [ABSTRACT FROM AUTHOR]

Ruthenium complexes containing a new type of phosphine ligand were obtained through photochemical transformations. The process involves the irradiation of (phosphinoferrocenylcarbonyl) ruthenium derivatives with visible light (tungsten halogen lamp) to yield complexes with κ2-P,O phosphinofulvene enolate ligands after the formal loss of the "CpFe+" (Cp = cyclopentadienyl) entity. A tandem reaction that involves the irradiation of a mixture of a (hydroxymethyl)ferrocenylphosphine ligand and (arene)ruthenium precursors is also possible. The reaction proceeds through the coordination of the hydroxy phosphine ligands, evolution to hydrido ketone (or hydrido aldehyde) complexes and subsequent evolution to the fulvene derivatives. The process also occurs under solar radiation. The photolysis reaction was studied at different wavelengths of the visible spectrum by irradiation with light-emitting diodes (LEDs). Positive results were obtained when irradiation was performed in the wavelength region corresponding to the metal-to-ligand charge-transfer (MLCT) band that is characteristic of the acylferrocenyl moiety. The use of green light (λ = 530 nm) gave the best results, and the reaction did not proceed under higher-wavelength light or in the dark. A non-coordinated phosphinoferrocenylcarbaldehyde ligand also evolved under solar radiation, but a complex mixture was obtained; thus, the selectivity increases significantly if the ruthenium centre is present. [ABSTRACT FROM AUTHOR]

A new class of superacids was designed using enolic derivatives of fulvene. After deprotonation, bond rearrangement leads in a stable conjugate base with an aromatic cyclopentadienyl ring and a carboxyl group. The gas phase enthalpies ( [ABSTRACT FROM AUTHOR]

Two new acceptors containing platinum-carbazole ( 1) and platinum-triphenylamine ( 2) backbones with bite angles of 90° and 120°, respectively, have been synthesised and characterised. Reactions of the rigid acceptor 1 with linear dipyridyl-based donors ( 3 and 4) generated [4+4] self-assembled molecular squares ( 5 and 6), and similar treatments with acceptor 2 instead of 1 yielded [6+6] self-assembled molecular hexagons ( 7 and 8). The metallacycles were characterised by multinuclear NMR spectroscopy (1H and 31P) and ESI-MS. The geometries of the metallacycles were optimised by using the PM6 method. When aggregates of the metallacycles were formed by adding hexane solutions in dichloromethane, aggregation-induced emission was observed for metallacycles 5 and 7, and aggregation-caused quenching was observed for metallacycles 6 and 8. The formation of aggregates was verified by dynamic light scattering and TEM analyses. Macrocycles 5 and 7 are white-light emitters in THF. Moreover, their high luminescence in both solution and the solid state was utilised for the recognition of nitroaromatic explosives. [ABSTRACT FROM AUTHOR]

Multimode molecular switches incorporating distinct and independently addressable functional components have potential applications as advanced switches and logic gates for molecular electronics and memory storage devices. Herein, we describe the synthesis and characterization of four switches based on the dihydroazulene/vinylheptafulvene (DHA/VHF) photo/thermoswitch pair functionalized with the ruthenium-based Cp*(dppe)Ru ([Ru*]) metal complex (dppe=1,2-bis(diphenylphosphino)ethane; Cp*=pentamethylcyclopentadienyl). The [Ru*]-DHA conjugates can potentially exist in six different states accessible by alternation between DHA/VHF, RuII/RuIII, and alkynyl/vinylidene, which can be individually stimulated by using light/heat, oxidation/reduction, and acid/base. Access to the full range of states was found to be strongly dependent on the electronic communication between the metal center and the organic photoswitch in these [Ru*]-DHA conjugates. Detailed electrochemical, spectroscopic (UV/Vis, IR, NMR), and X-ray crystallographic studies indeed reveal significant electronic interactions between the two moieties. When in direct conjugation, the ruthenium metal center was found to quench the photochemical ring-opening of DHA, which in one case could be restored by protonation or oxidation, allowing conversion to the VHF state. [ABSTRACT FROM AUTHOR]

Aza- and diazafulvenium methide systems are versatile building blocks for the synthesis of pyrroles and pyrazoles. These extended dipoles participate in sigmatropic [1,8]H shifts and 1,7-electrocyclizations giving vinyl pyrroles and pyrazoles. Under flash vacuum pyrolysis conditions these heterocycles undergo interesting rearrangements. Aza- and diazafulvenium methides can be intercepted by dipolarophiles. Derivatives with carboxylate groups at C-4 and/or C-5 act exclusively as 1,7-dipoles affording products resulting from the addition across the 1,7-positions. These 1,7-cycloadducts include chlorin and bacteriochlorin type macrocycles as well as steroidal analogues, compounds with relevance in medicinal chemistry. In contrast with this chemical behavior, 5-trifluoromethylazafulvenium methides can participate in both 1,7- and 1,3-dipolar cycloadditions. The generation and reactivity of benzodiazafulvenium methides is also discussed. [ABSTRACT FROM AUTHOR]

New polymers containing intact pendant-fulvene moieties have been successfully prepared from 1,3-phenyl-6-norbornenylfulvene via ring-opening metathesis polymerization (ROMP). The prepared polyfulvenes have unique electrochemical and photophysical properties which make them interesting candidates for light harvesting materials. [ABSTRACT FROM AUTHOR]