Nucleophilic Fluoroalkylation of α,β‐Unsaturated Carbonyl Compounds with α‐Fluorinated Sulfones: Investigation of the Reversibility of 1,2‐Additions and the Formation of 1,4‐Adducts

A detailed investigation of the reactions of PhSO₂CF₂H and PhSO₂CH₂F with (E)‐chalcone (=(E)‐1,3‐diphenylprop‐2‐en‐1‐one) at low temperatures revealed that these two reactions were kinetically controlled, and the ratios of 1,2‐ vs. 1,4‐adducts, which did not change much over time at these temperatures, reflect the relative rates of the two reaction pathways. The controlled experiments of converting the PhSO₂CF₂‐ and PhSO₂CHF‐substituted 1,2‐adducts to 1,4‐adducts showed that these isomerizations are not favored due to the low stability and hard‐soft nature of PhSO₂CF and PhSO₂CHF^? anions. Moreover, taking advantage of the remarkable stability and softness of (PhSO₂)₂CF^? anion, an efficient thermodynamically controlled isomerization of (PhSO₂)₂CF‐substituted 1,2‐adduct to 1,4‐adduct was achieved for the first time.     

Photophysical Properties of Intramolecular Charge Transfer in a Tribranched Donor–π–Acceptor Chromophore

The photophysical properties of intramolecular charge transfer (ICT) in a novel tribranched donor–π–acceptor chromophore, triphenoxazine‐2,4,6‐triphenyl‐1,3,5‐triazine (tri‐PXZ‐TRZ), with thermally activated delayed fluorescence character was investigated in different aprotic solvents by steady‐state spectroscopy and femtosecond and nanosecond transient absorption spectroscopy measurements. Increasing the solvent polarity led to a significant increase in the Stokes shift. The large Stokes shift in highly polar solvents was attributed to ICT properties upon excitation; this resulted in a strong interaction between the tri‐PXZ‐TRZ molecule and the surrounding solvent, which led to a strong solvation process. Quantum‐chemical calculations and changes in the dipole moment showed that this compound has a large degree of ICT. Furthermore, an apolar environment helped to preserve the symmetry of tri‐PXZ‐TRZ and to enhance its emission efficiency. The femtosecond and nanosecond transient absorption spectroscopy results indicated that the excited‐state dynamics of this push–pull molecule were strongly influenced by solvent polarity through the formation of a solvent‐stabilized ICT state. The excited‐state relaxation mechanism of tri‐PXZ‐TRZ was proposed by performing target model analysis on the femtosecond transient absorption spectra. In addition, the delayed fluorescence of tri‐PXZ‐TRZ was significantly modulated by a potential competition between solvation and intersystem crossing processes.     

Charge Transfer Through Dithieno[2,3‐a:3′,2′‐c]phenazine: Effect of Substitution Pattern on the Optoelectronic Properties of Regioisomeric Luminophores

Two series of regioisomeric luminophores that contained a dithieno[2,3‐a:3′,2′‐c]phenazine (DTP) unit as an electron acceptor have been designed and synthesized. To investigate the effect of substitution pattern on the optoelectronic properties of these luminophores, electron donors (N,N‐dihexylaniline or N,N‐dihexyl‐4‐vinylaniline) were incorporated at the 2,5‐, 8,11‐, and 9,10‐positions of the DTP unit. We found that the optoelectronic properties of the regioisomeric luminophores were greatly affected by the substitution pattern: functionalization at the 8,11‐positions of the DTP unit was superior to the other two substitution patterns in extending the effective π‐conjugation and strengthening the intramolecular charge‐transfer interactions. Moreover, the insertion of vinyl groups between the DTP and N,N‐dihexylaniline units narrowed the energy band‐gap for isomers 4 and 5 . However, hypsochromically shifted absorption and photoluminescence maxima were observed for isomeric luminophore 6 , in which electron donors were substituted at the 2,5‐positions of the DTP unit. These results should facilitate greater understanding of the structure–property relationships in regioisomeric semiconductors and present a new way to design optoelectronic materials with effective substitution patterns.     

Multi‐Responsive Supramolecular Gels Based on Charge Transfer Interactions

We report the co‐assembly of aromatic donor (D) and acceptor (A) molecules into purple sponge‐like supramolecular gels through susceptible charge transfer interactions with the aid of solvophobic interactions. The gel remained intact with the addition of up to 23 % (v/v) of nonpolar good solvents, such as toluene and xylene, but dissociated in the presence of <2 % (v/v) of polar solvents, such as tetrahydrofuran, ethyl acetate, and alcohols, with highly distinguishable changes of color. Notably, the gel dissolved within 1 min and the solution turned blue when 0.1 % (v/v) of methanol was added. The response to trifluoroacetic acid was extremely sensitive (i.e., the gel vanished immediately in the presence of 2 equivalents of trifluoroacetic acid), and the subsequent addition of trimethylamine could recover the purple gel. The multiple and visible response thus render the D–A gels as a potential detector for sensing complex chemical environments.     

Visible‐Light‐Mediated Synthesis of β‐Chloro Ketones from Aryl Cyclopropanes

We report the visible‐light‐mediated synthesis of β‐chloro ketones from aryl cyclopropanes, oxygen, hydrochloric acid, and nitric acid. The operationally simple and catalyst‐free method uses cheap standard laboratory reagents and displays broad functional‐group tolerance. Moreover, scale up of the reaction and late‐stage functionalization of bioactive compounds is possible, providing the opportunity to utilize the cyclopropane ring as a masked β‐chloro ketone in a reaction sequence. We propose a light‐driven radical chain reaction initiated by the reaction of diluted hydrochloric and nitric acid to produce small quantities of molecular chlorine. The mechanistic hypothesis is supported by ¹⁸O labelling and UV/Vis experiments, cyclovoltammetry, and several control reactions.     

Imidazole as a Donor/Acceptor Unit in Charge‐Transfer Chromophores with Extended π‐Linkers

Eleven new, stable, push–pull systems that feature 4,5‐bis[4‐(N,N‐dimethylamino)phenyl]imidazole and 4,5‐dicyanoimidazole as the donor and acceptor moieties and the systematically extended and varied π‐linker were prepared and investigated. Evaluation of the measured UV/Vis spectra, electrochemical data (cyclic voltammetry (CV), rotating‐disc voltammetry (RDV), and polarography) and calculated β and γ polarizabilities showed efficient charge transfer (CT) in biimidazole‐type chromophores. Push–pull system 27 , which features a planar thiophene‐derived π‐linker, was revealed to be the most efficient chromophore within the studied series. This chromophore possessed the most bathochromically shifted CT band, the lowest electrochemical gap, and highest β and γ polarizabilities. The CT transition was most significantly affected by structural features such as π‐linker length, planarity, conjugating arrangement, and the presence of olefinic/acetylenic or 1,4‐phenylene/thiophene subunits in the π‐linker.     

A Mild Isomerization Reaction for β,γ‐Unsaturated Ketone to α,β‐Unsaturated Ketone

A series of β,γ‐unsaturated ketones were isomerized to their corresponding α,β‐unsaturated ketones by the introduction of DABCO in iPrOH at room temperature. The endo‐cyclic double bond (β,γ‐position) on ketone was rearranged to exo‐cyclic double bond (α,β‐position) under the reaction conditions.     

Visible Light Promoted β‐C—H Alkylation of β‐Ketocarbonyls via a β‐Enaminyl Radical Intermediate

A 5πe carbonyl activation mode is reported on the basis of photo‐induced single‐electron‐transfer (SET) oxidation of a secondary enamine. The resultant β‐enaminyl radical intermediate was trapped by a wide range of Michael acceptors, producing β‐alkylation products of β‐ketocarbonyls in a highly efficient manner.     

Ferrocene‐Donor and 4,5‐Dicyanoimidazole‐Acceptor Moieties in Charge‐Transfer Chromophores with π Linkers Tailored for Second‐Order Nonlinear Optics

A series of new nonlinear optical chromophores ( 1 – 15 ) that were comprised of ferrocene‐donor and 4,5‐dicyanoimidazole‐acceptor moieties and various π linkers of different length were synthesized. Support for the presence of significant D ? A interactions in these NLO‐phores was obtained from the evaluation of the quinoid character of the 1,4‐phenylene moieties and their electronic absorption spectra, which featured intense high‐energy (HE) bands that were accompanied by less‐intense low‐energy (LE) bands. The redox behavior of these compounds was investigated by cyclic voltammetry (CV) and by rotating‐disc voltammetry (RDV); their electrochemical gaps decreased steadily from 2.64 to 2.09 V. In addition to the experimentally obtained data, DFT calculations of their absorption spectra, HOMO/LUMO levels, and second‐order polarizabilities (β) (?2ω,ω,ω) were performed. A structure–property relationship study that was performed by systematically altering the π linker revealed that the intramolecular charge‐transfer and nonlinear optical properties of these inorganic–organic hybrid D? π? A systems ( 1 – 15 ) were primarily affected by: 1) The presence of olefinic/acetylenic subunits; 2) the length of the π linker; and 3) the spatial arrangement (planarity) of the π linker.     

Organocatalytic Enantioselective Synthesis of Tetrasubstituted α‐Amino Allenoates by Dearomative γ‐Addition of 2,3‐Disubstituted Indoles to β,γ‐Alkynyl‐α‐imino Esters

The first asymmetric synthesis of tetrasubstituted α‐amino allenoates by a chiral phosphoric acid catalyzed dearomative γ‐addition reaction of 2,3‐disubstituted indoles to β,γ‐alkynyl‐α‐imino esters is reported. This method provides access to a series of highly functionalized tetrasubstituted allenes featuring quaternary stereocenters in high yields, and with excellent regio‐, diastereo‐, and enantioselectivities under mild conditions without by‐product formation. Representative large‐scale reactions and diverse transformations of the products into various scaffolds with potential biological activities render are also disclosed. The mechanism of the reaction was elucidated by control reactions and DFT calculations.     

Synthesis of β‐Haloketones by β‐Addition Reactions of α,β‐Unsaturated Ketones with BX3 (X = Br,Cl) as Halide Source

A series of β‐bromoketones and β‐chloroketones were synthesized by the addition reactions of α,β‐unsaturated ketones under BX₃ (X = Br, Cl) and ethylene glycol reaction system. The α,β‐unsaturated ester also was successfully converted to its corresponding β‐bromoester under the reaction condition.     

A New V‐Shaped Organic Fluorescent Compound Integrated with Crystallization‐Induced Emission Enhancement and Intramolecular Charge Transfer

The emission behavior of a new V‐shaped organic fluorescent compound (p,p′‐bis(2‐aryl‐1,3,4‐oxadiazol‐5‐yl)diphenyl sulfone ( OZA-SO ), consisting of diethylamino (donor) and sulfone (acceptor) units, has been studied in various polar solvents and with different morphologies. As expected, there is the gradual transition from the locally excited state to the intramolecular charge‐transfer (ICT) state with the increasing solvent polarity. The photoluminescence intensity of OZA-SO initially decreases with a low water fraction (f_w), owing to ICT effect, and then increases with a high f_w, owing to crystallization‐induced emission enhancement. At the same time, the fluorescence lifetime of OZA-SO increases from 0.062 ns in dimethylformamide (DMF) to 5.80 ns in a solution containing 90 % water, and then to 7.49 ns in a solution containing 60 % water. Furthermore, the solid‐state emission of OZA-SO can be tuned reversibly from green to yellow by fuming/grinding or fuming/heating owing to morphological changes. This color‐switchable feature of OZA-SO may have potential applications in optical‐recording and temperature‐sensing materials.     

Synthesis of new optically active α,α′,β‐trisubstituted‐β‐lactones as monomers for stereoregular biopolyesters

Various optically active (4R)‐alkyloxycarbonyl‐3,3‐dialkyl‐2‐oxetanones as monomers were synthesized from L‐(S)‐malic acid in six steps to prepare a new family of stereopolyesters for biomedical applications. The synthesis began with an esterification followed of a dialkylation in the aim to introduce hydrophobic groups as methyl or reactive group as allyl. Then, a saponification has permitted to obtain the corresponding diacids that reacted with appropriate alcohols to furnish different monoesters. The last and most important step was activation of hydroxyl group of monoesters with the asymmetric carbon configuration inversion according to the Mitsunobu reaction. Thus, this reaction has provided lactones from monoesters with 100% enantiomeric excess which was confirmed by ¹H NMR and by the synthesis of corresponding isotactic and semicrystalline homopolyesters. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2586–2597     

Tuning the Rates of Long‐Range Charge Transfer across Phenylene Wires

Walking a tight wire: Phototriggered charge transfer across a tetra‐p‐dimethoxybenzene bridge is three orders of magnitude faster than that across a structurally similar tetra‐p‐xylene spacer, despite equal reaction driving forces in both cases (see picture). This result is interpreted in terms of markedly different donor–bridge energy gaps.

     

Intense Ground‐State Charge‐Transfer Interactions in Low‐Bandgap,Panchromatic Phthalocyanine–Tetracyanobuta‐1,3‐diene Conjugates

A cycloaddition–retroelectrocyclization reaction between tetracyanoethylene and two zinc phthalocyanines (Zn^IIPcs) bearing one or four anilino‐substituted alkynes has been used to install a strong, electron‐accepting tetracyanobuta‐1,3‐diene (TCBD) between the electron‐rich Zn^IIPc and aniline moieties. A combination of photophysical, electrochemical, and spectroelectrochemical investigations with the Zn^IIPc‐TCBD‐aniline conjugates, which present panchromatic absorptions in the visible region extending all the way to the near infrared, show that the formal replacement of the triple bond by TCBD has a dramatic effect on their ground‐ and excited‐state features. In particular, the formation of extremely intense, ground‐state charge‐transfer interactions between Zn^IIPc and the electron‐accepting TCBD were observed, something unprecedented not only in Pc chemistry but also in TCBD‐based porphyrinoid systems.     

Synthesis of Phenanthrene Derivatives through the Reaction of an α,α‐Dicyanoolefin with α,β‐Unsaturated Carbonyl Compounds

Phenanthrene derivatives were prepared by reacting an α,α‐dicyanoolefin with different α,β‐unsaturated carbonyl compounds resulting from Wittig reaction of ninhydrin and phosphanylidene or condensation of barbituric acid and an aldehyde. The easy procedure, mild and metal‐catalyst free, reaction conditions, good yields, and no need for chromatographic purifications are important features of this protocol. The structures of the product of type 3 and 5 were corroborated spectroscopically (IR, ¹H‐ and ¹³C‐NMR, and EI‐MS). A plausible mechanism for this type of reaction is proposed (Scheme 1).     

Asymmetric Dearomative Fluorination of 2‐Naphthols with a Dicarboxylate Phase‐Transfer Catalyst

A linked dicarboxylate phase‐transfer catalyst enables smooth asymmetric dearomative fluorination of 2‐naphthols with Selectfluor under mild conditions to give the corresponding 1‐fluoronaphthalenone derivatives in a highly enantioselective manner. This reaction, which is compatible with a range of functional groups, is the first example of catalytic asymmetric fluorination of 2‐naphthols, and is expected to be useful in the synthesis of bioactive molecules.