Bicyclic Dienes Research Articles

Strain Engineered Bridged Bicyclic Diene Photoswitches in the Race of Next‐Generation Molecular Solar Thermal Energy Storage

AbstractNorbornadiene/Quadricyclane (NBD/QC) is a prototypical bridged bicyclic diene (BBD)‐based photoswitch that has been well‐studied for molecular solar thermal energy storage (MOST). Inspired by the recent synthetically accessed BBDs, herein several photoswitches are rationally designed with modulated ring strain energies (RSE) in photoisomers to incorporate high energy storage density (ESD) and storage time in a single couple. The storage energy ( ) calculated at DLPNO‐CCSD(T)/Def2TZVP level is correlated with difference in RSE of two isomers (ΔRSE) whereas thermal back reaction (TBR) barrier calculated at (8,8)‐CASPT2/6‐311++G** shows correlation with RSE in metastable photoproduct. On the basis of these structure‐property‐RSE relationships, we recognized that two photoisomers need not to be highly strained. Instead, the RSE in the photoproduct and diene should be minimized while maintaining a large enthalpy difference between them to increase ESD and extend energy storage times in a single photoswitch. TBR barrier is governed by RSE in photoproduct and increasing strain in photoproduct may improve the but at the cost of the TBR barrier. Herein, the structural skeletons are explored that holds promise to remarkably improve thermochemical properties relative to the unsubstituted BBD‐based photoswitches reported so far. The BBD molecules with short saturated bridge length but elongated unsaturated bridges could bestow desirable thermochemical parameters and can be regarded as excellent candidates for MOST application. The work lays a theoretical foundation that guides to improve thermochemical properties via strain engineering of BBD‐based photoswitches and opens a new avenue for designing principles and future experimental investigations of MOST systems.

Novel route to enhance the thermo-optical performance of bicyclic diene photoswitches for solar thermal batteries.

Harnessing solar energy by employing chemical photoswitches in molecular solar thermal (MOST) energy storage systems is a topic of appealing research interest. However, incorporating all the features desired for an ideal MOST system in a single photoswitching couple is challenging. Inspired by experimental synthesis, herein we report our attempt to enhance both the thermochemical and photophysical properties in a single-bridged bicyclic diene (BBD)-based photoswitch by elongating the unsaturated bridge with different heteroatomic units. To elucidate the best elongation unit, the energy storage capacity and the TBR barriers were accounted using the DLPNO-CCSD(T) and (8,8)-CASPT2 methods, respectively. The photophysical properties including the absorption onset, excitation wavelengths, and the absorption intensities were extensively investigated with the time-dependent calculations. The result provides information on the most versatile solvent to exhibit the best photoswitching behaviour which is beneficial for real-life energy storage applications. Additionally, the stability and reversibility of the photoswitching system with elongated unsaturated bridges have also been assessed. By means of the studied modification, the storage energy of 158.57 kJ/mol, energy storage density of 1.48 MJ/kg, TBR barrier of 136.36 kJ/mol, and the absorption onset of 305.00 nm is achieved in acetonitrile. These values are substantially higher when compared with the storage energy (96.06 kJ/mol), energy storage density (1.04 MJ/kg), and TBR barrier (121.76 kJ/mol) of prototype NBD/QC in the gas phase. The outcomes render useful insights into the stability and properties of bicyclic diene-based photoswitches having elongated unsaturated bridges and indeed paves the way for the rational design of practical MOST systems.

Searching the Chemical Space of Bicyclic Dienes for Molecular Solar Thermal Energy Storage Candidates.

Photoswitches are molecular systems that are chemically transformed subsequent to interaction with light and they find potential application in many new technologies. The design and discovery of photoswitch candidates require intricate molecular engineering of a range of properties to optimize a candidate to a specific applications, a task which can be tackled efficiently using quantum chemical screening procedures. In this paper, we perform a large scale screening of approximately half a million bicyclic diene photoswitches in the context of molecular solar thermal energy storage using ab initio quantum chemical methods. We further device an efficient strategy for scoring the systems based on their predicted solar energy conversion efficiency and elucidate potential pitfalls of this approach. Our search through the chemical space of bicyclic dienes reveals systems with unprecedented solar energy conversion efficiencies and storage densities that show promising design guidelines for next generation molecular solar thermal energy storage systems.

Searching the Chemical Space of Bicyclic Dienes for Molecular Solar Thermal Energy Storage Candidates

AbstractPhotoswitches are molecular systems that are chemically transformed subsequent to interaction with light and they find potential application in many new technologies. The design and discovery of photoswitch candidates require intricate molecular engineering of a range of properties to optimize a candidate to a specific applications, a task which can be tackled efficiently using quantum chemical screening procedures. In this paper, we perform a large scale screening of approximately half a million bicyclic diene photoswitches in the context of molecular solar thermal energy storage using ab initio quantum chemical methods. We further device an efficient strategy for scoring the systems based on their predicted solar energy conversion efficiency and elucidate potential pitfalls of this approach. Our search through the chemical space of bicyclic dienes reveals systems with unprecedented solar energy conversion efficiencies and storage densities that show promising design guidelines for next generation molecular solar thermal energy storage systems.

Prospects of Improving Molecular Solar Energy Storage of the Norbornadiene/Quadricyclane System through Bridgehead Modifications.

We have investigated novel bicyclic diene molecular solar thermal energy storage systems that presently are the ones with the highest predicted energy density. Using a variety of different ab initio quantum chemical methods, we report storage energies, absorption spectra, and reaction barriers for the release of stored energy for a series of bicyclic dienes. The bicyclic dienes are all constructed by modifying the bridgehead of the well-known norbornadiene/quadricyclane (NBD/QC) system. In conclusion, we find it promising that it is possible to significantly amplify the storage energy of the NBD/QC system without seriously compromising other crucial properties by introducing simple modifications to the bridgehead.

Stereoselective Synthesis of Hydrindane and Hydroazulene Derivatives by Transannular Cyclization of Nine- and Ten-Membered Carbocycles.

Treatment of cis-fused bicyclic diene dicarboxylates with Li/naphthalene triggers a tandem ring-opening and transannular cyclization process that stereoselectively yields hydroazulenes and hydrindanes derivatives. Cyclononadienyl diesters, which can be isolated after the ring-opening step by judicious choice of the reaction conditions, undergo a tandem conjugate addition/intramolecular Michael addition upon treatment with chiral lithium amides to give bicyclic β-amino esters in a process where 4 contiguous stereocenters are formed with high diastereocontrol. A concise route toward the highly enantioenriched AEF ring core of the aconitine-type alkaloids has been developed as an application of this methodology. The starting cis-fused bicyclic dicarboxylates are easily prepared in one step by reductive alkylation of diisopropyl phthalate (Na/THF, followed by the appropriate bis-electrophiles).

Synthesis of new ruthenium complexes and their use as catalysts in the hydrogenation of diene compounds

Ruthenium half-sandwich complexes [Cp*Ru (diene compound)]+X− containing various commercially available diene compounds as ligands were tested as catalysts for the hydrogenation of diene compounds. Complexes containing acyclic, cyclic, bicyclic dienes, and α,β-unsaturated carboxylic acids and their derivatives as diene ligands were successfully prepared. The anionic part of the complexes (X−) was represented by triflate, perchlorate and tetrafluoroborate ions. Hydrogenations were carried out in homogeneous and heterogeneous arrangements. The desired products with Z-configuration of the double bond were formed with high selectivity (95–99%) in both cases. It was found out that selectivity was influenced neither by the type of diene ligand nor by the type of the anionic part of the complex. The hydrogenation rate was influenced by the type and the size of the diene ligand. The rate of hydrogenation of diene using complexes containing isolated cyclic or bicyclic ligands was the highest. The lowest reaction rates were observed using complexes with acyclic dienes. The influence of the type of the anionic part of the complex on the reaction rate was also studied. The lowest rate of hydrogenation was observed using complexes with tetrafluoroborate anion. The difference in reaction rates using complexes with triflate and perchlorate anions was not significant. This work added important information for the understanding the mechanism of diene hydrogenation using ruthenium half-sandwich complexes.

Dispersive Optical Activity of (R)-Methylene Norbornene: Intrinsic Response and Solvation Effects.

The dispersive optical activity of a homoconjugated bicyclic diene, (R)-methylene norbornene (R-MNB), was interrogated under complementary vapor-phase and solution-phase conditions to elucidate the structural/electronic provenance of its unusual chiroptical signatures and to explore the marked influence of environmental perturbations. The intrinsic (isolated-molecule) values of specific rotation measured at 355 and 633 nm (1623.5 ± 5.5 and 390.4 ± 3.7 deg dm-1 (g/mL)-1) were found to be factors of 3.9 and 2.1 smaller in magnitude than analogous quantities obtained for the kindred enone, (R)-norbornenone (R-NBO), reflecting, in part, the loss of prominent magnetic-dipole contributions from the C═O moiety and the exclusion of electron delocalization from the oxygen lone pairs. The wavelength-resolved rotatory powers of R-MNB were enhanced dramatically (by ∼40% on average) upon dissolution in any of the four common solvents targeted by the present study (acetonitrile, di-n-butylether, cyclohexane, and chloroform), yet displayed only a slight dependence on the exact nature of the surrounding liquid (±2.7% variation from the mean at 589.3 nm). Quantum-chemical calculations built upon the linear-response frameworks of density-functional theory and coupled-cluster theory were enlisted to interpret experimental results, with the substantial effects incurred by nonspecific solvation phenomena being explored through use of polarizable continuum models and bulk property-response relationships. Aside from enumerating the varied quality of agreement attained between computational predictions and polarimetric measurements, these efforts have found that refractive-index correlations, akin to those embodied in the venerable (albeit often discounted) Lorentz local-field correction, afford a viable means of linking the chiroptical behavior of R-MNB across phases.

Radiolysis products of the cyclohexane–bicyclic diene binary system

Solutions of 5-vinyl-2-norbornene (VNB, 5-vinylbicyclo[2.2.1]hept-2-ene) and the related compounds 5-ethylidene-2-norbornene (ENB, 5-ethylidenbicyclo[2.2.1]hept-2-ene) and 2-vinyl-2-norbornane (VNN, 2-vinylbicyclo[2.2.1]heptane) in cyclohexane have been irradiated with γ-rays at 40°C. The initial radiation-chemical yields G 0 for the consumption of the solutes and the formation of final products of γ-radiolysis of the solvent cyclohexane have been determined. It has been shown that solute consumption and molecular hydrogen formation yields G 0(−RH) and G 0(H2), respectively, are linearly related to the first vertical ionization potential of the solute. The G 0 values of molecular hydrogen, cyclopentadiene (CPD), butadiene, and methylallene, minor products of γ-radiolysis (40°C) of liquid VNB, ENB, and dicyclopentadiene (tricyclo[5.2.1.02.6]decadiene-3.8), have been determined. It has been shown that the G 0 values of CPD formation linearly depend on the first vertical ionization potentials of γ-irradiated bicyclic dienes. It is concluded that the γ-irradiation of cyclohexane generates two kinds of radical cations, which differ in mobility and reactivity.

General Route to Cyclobutadiene Rhodium Complexes.

Cyclobutadiene rhodium complexes bear high potential for applications in organometallic synthesis and catalysis. We have found that the cyclobutadiene complexes with substitutionally labile p-xylene ligands [(C4 R4 )Rh(p-xylene)](+) can be synthesized in one step from the commercially available bis(ethylene) complex [{(C2 H4 )2 RhCl}2 ], p-xylene, and internal alkynes. The replacement of p-xylene by various ligands provides a general access to other [(C4 R4 )Rh] compounds, such as [(C4 R4 )RhCl]x , [(C4 R4 )RhL3 ](+) , [(C4 R4 )Rh(C5 H5 )], and [(C4 R4 )Rh(arene)](+) . Complex [(C4 Et4 )Rh(p-xylene)](+) also catalyzes an unusual cycloisomerization of a 1,11-dien-6-yne into a bicyclic diene.

Cobalt-Mediated η5-Pentadienyl/Alkyne [5 + 2] Cycloaddition Reactions: Substitution Effects, Bicyclic Synthesis, and Photochemical η4-Cycloheptadiene Demetalation

The preparation of seven-membered carbocycles via traditional organic synthesis is difficult, yet essential, due to the prevalence of these moieties in bioactive compounds. As we report, the Co-mediated pentadienyl/alkyne [5 + 2] cycloaddition reaction generates kinetically stable η2,η3-cycloheptadienyl complexes in high yield at room temperature, which isomerize to the thermodynamically preferred η5-cycloheptadienyl complexes upon heating at 60–70 °C. Here we describe an extended investigation of this reaction manifold, exploring substituent effects and extending the reaction to tandem cycloaddition/nucleophilic cyclizations, generating fused bicyclic compounds. We also describe a new high-yielding photolytic method for the decomplexation of organic cycloheptadienes from Co(I) complexes. Both C5Me5 (Cp*) and C5H5 (Cp) half-sandwich complexes are active in [5 + 2] cycloaddition with alkynes, with Cp* generally providing higher yields of cycloheptadienyl complexes. Cp cycloheptadienyl complexes, however, are resistant to thermal η2,η3 → η5 isomerization. The reaction remains limited to open pentadienyl complexes incorporating substituents in the terminal (1 and 5) positions, except for the unsubstituted CpCo(η5-cycloheptadienyl)+ complex, which is modestly reactive. Incorporation of tethered latent nucleophiles allows cyclization onto the intermediate cycloheptadienyl cations, producing bicyclo[5.3.0]decadiene and bicyclo[5.4.0]undecadiene systems with complete diastereocontrol. A selection of intermediate complexes have been crystallographically characterized. Addition of tethered malonate nucleophiles occurs reversibly with equilibration to a thermodynamic elimination product, while enolate nucleophiles cyclize reliably under kinetic control. The resulting bicyclic products are decomplexed in high (>90%) yield by UV photolysis in the presence of allyl bromide to provide the organic bicyclic diene with complete retention of ring fusion geometry and without double-bond isomerization.

ChemInform Abstract: Enantioselective Rhodium‐Catalyzed Allylation of Cyclic Imines with Potassium Allyltrifluoroborates.

AbstractThe asymmetric reaction of different types of cyclic imines with a range of allyltrifluoroborates is described using a rhodium complex catalyst having a chiral bicyclic diene as ligand.

Synthesis of thermally degradable epoxy adhesives

ABSTRACTWe have developed a new strategy for the synthesis of epoxide‐containing polymers where the pendant reactive groups are connected to the main backbone via thermally labile oxonorbornene groups. The polymers were synthesized by radical 1,4‐polymerization of the appropriate bicyclic diene monomer. The produced polymers can be crosslinked in the presence of a diamine and de‐crosslinked by thermal treatment at 160 °C, which induces retro‐Diels–Alder reaction and cleaves pendant groups from the polymer backbone, as confirmed by differential scanning calorimetry. The potential for the utilization of this polymer as a thermally removable adhesive was demonstrated by a simple adhesion test. This method provides access to thermally cleavable epoxy networks that can be quickly and irreversibly disintegrated into nonvolatile components upon heating to a specified temperature. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4992–4997

Stereoselective Synthesis of a Bicyclic Norsesquiterpene Backbone – A Possible Route to Nardosinane Derivatives

AbstractWe have developed an efficient diastereoselective synthetic route towards a nardosinane sesquiterpene scaffold. The strategy used a key bicyclic diene intermediate 11a, and allowed access to valuable polyoxygenated sesquiterpenes 21 and 22, which may be regarded as analogues of the natural sesquiterpenes laevinol B and fulvol acetate, respectively.

Synthesis of Chiral Olefin Ligands and their Application in Asymmetric Catalysis

AbstractChiral olefins have recently emerged as among the most promising ligands for asymmetric catalysis. In the past nearly ten years, significant advances have been made in developing ligands, including diene and heteroatom/olefin hybrid ligands, and exploring their applications in challenging metal‐catalyzed asymmetric reactions. Especially in some cases, chiral olefin ligands have an obvious advantage over some conventional chiral ligands in terms of activity and selectivity. Besides the most often studied rigidly bicyclic dienes, readily accessible chiral‐chain dienes with flexible frameworks and two terminal olefins as coordinating groups have also proven to be effective for achieving high levels of enantioselectivity in transition‐metal‐catalyzed asymmetric reactions. Moreover, the terminal olefins can be combined with phosphorus atoms on suitable chiral skeletons for the development of novel phosphorus/olefin (P/olefin) hybrid ligands, which have high activity and selectivity in Pd‐catalyzed asymmetric transformations. Significantly, sulfur/olefin (S/olefin) hybrid ligands have been successfully explored and applied in a range of Rh‐catalyzed asymmetric transformations. This Focus Review will mainly discuss the synthesis of recently developed chiral‐chain diene ligands, phosphorus/terminal‐olefin hybrid ligands, and sulfur/olefin hybrid ligands, and their application in asymmetric catalysis.

ChemInform Abstract: Chiral Bicyclic [2.2.2] Octadiene Ligands for Rh‐Catalyzed Catalytic Asymmetric Conjugate Additions to Acyclic Enones: A Quantitative Structure—Property Relationship.

AbstractThe chiral bicyclic diene ligand shown appears to be the most effective one with respect to yield and enantioselectivity among 18 bicylic ligands studied.

Synthetic Studies Towards the Core Tricyclic Ring System of Pradimicin A

AbstractPradimicins are structurally intriguing natural products that possess potent biological activity as antifungal and antiviral agents through a unique mode of action as carbohydrate binding agents. A preliminary synthetic approach towards pradimicin A has focused on a model study of the core tricyclic ring system. The route features an alkoxyallylboration/cycloisomerization/Diels–Alder cycloaddition sequence as the key steps. The alkoxyallylboration was critical for differentiating the hydroxy groups in the central cyclohexadienediol unit of pradimycins, which will ensure a regiocontrolled glycosylation. For the cycloisomerization reaction, various substrates and conditions were tested for a ring‐closing enyne metathesis reaction. With enyne substrate 23, dimerization‐prone bicyclic diene 24 was isolated as the major product under the conditions of both ruthenium‐catalyzed metathesis and palladium‐catalyzed cycloisomerization. In the end, the optimal route found for the synthesis of the model functionalized tricyclic ring system 31 features a one‐pot sequential palladium‐catalyzed cycloisomerization, Diels–Alder reaction, and oxidative aromatization.

Soluble Polyacetylene Derivatives by Chain-Growth Polymerization of Dienes

A new method for the fabrication of soluble polyacetylene derivatives was developed based on bromination–dehydrobromination of bicyclic diene polymers. High molecular weight polymer precursors were...

ChemInform Abstract: Intramolecular Palladium(0)-Catalyzed Coupling of Enol Triflate and Vinylstannane Functions. New Annulation Sequences Leading to Bicyclic Diene Systems.

Abstract A new, concise annulation method leading to the efficient production of structurally novel bicyclic dienes has been developed. The individual synthetic steps that constitute this method, as outlined in general terms in Scheme 1, involve (a) the alkylation of (functionalized) carbonyl compounds with ϵ-iodo-2-trimethylstannyl-1-alkenes (17 → 21), (b) the conversion of the alkylatlon products into the corresponding enol trifluoromethanesulfonates (triflates) (21 → 22), and (c) the palladlum(0)-catalyzed intramolecular coupling of the enol triflate-vinylstannanes to provide the dienes (22 → 23). The generality of the method is demonstrated by the synthesis of functionalized bicyclo(4.3.0]nonane (61, 62, 65, 66), bicyclo[4.4.0]decane (63, 64, 67, 68, 71), bicyclo[5.3.0]decane (70), and bicyclo[5.4.0]undecane (69) derivatives.

Catalyst-controlled formal [4 + 3] cycloaddition applied to the total synthesis of (+)-barekoxide and (-)-barekol.

The tandem cyclopropanation/Cope rearrangement between bicyclic dienes and siloxyvinyldiazoacetate, catalyzed by the dirhodium catalyst Rh(2)(R-PTAD)(4), effectively accomplishes enantiodivergent [4 + 3] cycloadditions. The reaction proceeds by a cyclopropanation followed by a Cope rearrangement of the resulting divinylcyclopropane. This methodology was applied to the synthesis of (+)-barekoxide (1) and (-)-barekol (2).