噻吩螺烯的化学与光化学合成

本文综述了近年来噻吩螺烯的化学与光化学合成方面的重要进展。在螺烯的化学合成方面,阐明了单螺烯的常见合成手法,即以并三噻吩为构筑模块,合成螺烯前驱体联并三噻吩,其后通过硫代关环手法制备噻吩单螺烯。由于前驱体的两个并噻吩片段可能存在分子内的相互作用,造成无法无限制增长螺烯分子的尺寸。通过增加助溶基团的合成策略可以将螺烯的分子结构由单螺烯引入到双螺烯。在螺烯的光化学合成方面,光化学氧化关环的实例表明了光化学是构筑单螺烯与双螺烯的有效手法。由于存在前驱体双键在光照条件下可以打开产生双自由基的光化学反应机理,在其后关环步骤可有效产生外消旋体与内消旋体这样有趣的双螺烯产物。此外,本文针对噻吩螺烯领域的前景,提出了3个方面的观点:1)通过设计末端噻吩环上硫原子的位置异构,形成新的螺烯同分异构体;2)通过合成设计,可以制备新结构的双螺烯与多螺烯;3)通过手性拆分,可将螺烯旋光体应用于手性催化、手性组装等应用领域。     

Two types of two-component gels formed from pseudoenantiomeric ethynylhelicene oligomers

Two-component gels formed from pseudoenantiomeric ethynylhelicene oligomers in toluene exhibited two different properties depending on difference in numbers of helicenes in the two components. The combinations (M)-5/(P)-4, (M)-6/(P)-4, and (M)-7/(P)-4, which contained oligomers with comparable numbers of helicenes, formed transparent gels (Type I gels). The combinations (M)-6/(P)-3, (M)-7/(P)-3, and (M)-8/(P)-3, which contained oligomers with considerably different numbers of helicenes, formed turbid gels (Type II gels). Negative Cotton effects were observed for the Type I gels in the region between 350 and 450 nm, and were positive for the Type II gels, despite the use of (M)-oligomers for the longer components. UV/vis exhibited absorption maxima at 350 nm for the Type I gels and at 338 nm for the Type II gels. Different behaviors in gel formation processes were observed by fluorescence studies. Atomic force microscopy analysis showed fiber structures of 25-50 nm diameter for Type I gels and bundles of 100-150 nm diameter for Type II gels. The stoichiometry in gel formation also differed: The Type I gels showed 1:1 stoichiometry of the two components; the Type II gels showed no 1:1 stoichiometry, likely 1:2 stoichiometry. Using the Type I and II gels, two-layer gel systems were constructed.     

Symmetric,Unsymmetrical, and Asymmetric [7]‐, [10]‐, and [13]Helicenes

Fully aromatic helicenes with more than one pitch‐length are illustrious synthetic targets with potential applications in advanced optical devices and nano‐electronics. The task of extending the length of fully conjugated helicenes past one pitch length is challenging. Now, the synthesis of a series of azaoxa[7]‐, [10]‐, and [13]helicenes is described. The synthesis is based on iterative oxidative furan formation between 3,6‐dihydroxycarbazoles and/or 2‐naphthols. The flexibility of the presented method allows the convenient and scalable synthesis of symmetric, unsymmetrical, and asymmetric homo‐chiral structures. The [13]helicenes can be synthetically functionalized both at the termini and the periphery. The full range of helicenes were characterized using NMR and optical spectroscopy (UV/Vis, fluorescence, and CD) along with single‐crystal X‐ray crystallography. The enantiomers of the [13]helicenes are the longest optically pure helicenes isolated to date.     

Symmetric,Unsymmetrical, and Asymmetric [7]‐, [10]‐, and [13]Helicenes

Fully aromatic helicenes with more than one pitch‐length are illustrious synthetic targets with potential applications in advanced optical devices and nano‐electronics. The task of extending the length of fully conjugated helicenes past one pitch length is challenging. Now, the synthesis of a series of azaoxa[7]‐, [10]‐, and [13]helicenes is described. The synthesis is based on iterative oxidative furan formation between 3,6‐dihydroxycarbazoles and/or 2‐naphthols. The flexibility of the presented method allows the convenient and scalable synthesis of symmetric, unsymmetrical, and asymmetric homo‐chiral structures. The [13]helicenes can be synthetically functionalized both at the termini and the periphery. The full range of helicenes were characterized using NMR and optical spectroscopy (UV/Vis, fluorescence, and CD) along with single‐crystal X‐ray crystallography. The enantiomers of the [13]helicenes are the longest optically pure helicenes isolated to date.     

Multiple Helicenes Defected by Heteroatoms and Heptagons with Narrow Emissions and Superior Photoluminescence Quantum Yields**

The incorporation of heteroatoms and/or heptagons as the defects into helicenes expands the variety of chiroptical materials with novel properties. However, it is still challenging to construct novel boron-doped heptagon-containing helicenes with high photoluminescence quantum yields (PLQYs) and narrow full-width-at-half-maximum (FWHM) values. We report an efficient and scalable synthesis of a quadruple helicene 4Cz-NBN with two nitrogen-boron-nitrogen (NBN) units and a double helicene 4Cz-NBN-P1 bearing two NBN-doped heptagons, the latter could be formed via a two-fold Scholl reaction of the former. The helicenes 4Cz-NBN and 4Cz-NBN-P1 exhibit excellent PLQYs up to 99 % and 65 % with narrow FWHM of 24 nm and 22 nm, respectively. The emission wavelengths are tunable via stepwise titration experiments of 4Cz-NBN-P1 toward fluoride, enabling distinguished circularly polarized luminescence (CPL) from green, orange (4Cz-NBN-P1-F1) to yellow (trans/cis-4Cz-NBN-P1-F2) with near-unity PLQYs and broader circular dichroism (CD) ranges. The five structures of the aforementioned four helicenes were confirmed by single crystal X-ray diffraction analysis. This work provides a novel design strategy for construction of non-benzenoid multiple helicenes exhibiting narrow emissions with superior PLQYs.     

Syntheses and properties of enantiomerically pure higher (n > or = 7) [n-2]triangulanedimethanols and sigma-[n]helicenes

(P)-(+)-Hexaspiro[2.0.0.0. 0.0.2.1.1.1.1.1]pentadecane [(P)-17] as well as (M)-(-)- and (P)-(+)-octaspiro[2.0.0.0.0.0.0.0.2.1.1.1.1.1.1.1]nonadecanes [(M)- and (P)-25]-enantiomerically pure unbranched [7]- and [9]triangulanes-have been prepared starting from racemic THP-protected (methylenecyclopropyl)methanol 6. The relative configurations of all important intermediates as well as the absolute configurations of the key intermediates were established by X-ray crystal structure analyses. This new convergent approach to enantiomerically pure linear [n]triangulanes for n=7, 9 was also tested in two variants towards [15]triangulane. Some of the most prominent and unexpected features of the newly prepared compounds are the remarkable modes of self-assembly of the diols (P)-14, (E)-(3S,3'S,4S,4'S,5R,5'R)-21, (P)-(+)-22, and (E)-31 in the solid state through frameworks of intermolecular hydrogen bonds leading to, depending on the respective structure, nanotube- [(P)-14, (P)-(+)-22, and (E)-31], honeycomb-like structures [(E)-(3S,3'S,4S,4'S,5R,5'R)-21] or a supramolecular double helix [(P)-(+)- and (M)-(-)-22]. Liquid crystalline properties of the esters and ethers of the diols (P)-14, (P)-, and (M)-22 have also been tested. Although all of these [n]triangulanes have no chromophore which would lead to significant absorptions above 200 nm, they exhibit surprisingly high specific rotations even at 589 nm with [alpha](20)(D)=+672.9 (c=0.814 in CHCl(3)) for (P)-(+)-17, +909.9 (c=0.96 in CHCl(3)) for (P)-(+)-25, -890.5 (c=1.01 in CHCl(3)) for (M)-(-)-25, and -1302.5 (c=0.36 in CHCl(3)) for (M)-(-)-39, and the specific rotations increase drastically on going to shorter wavelengths. This outstanding rotatory power is in line with their rather rigid helical arrangement of sigma bonds, and accordingly these helically shaped unbranched [n]triangulanes may be termed "sigma-[n]helicenes", as they represent the sigma-bond analogues of the aromatic pi-[n]helicenes. Density functional theory (DFT) computations at the B3 LYP/6-31+G(d,p) level of theory for the geometry optimization and time-dependent DFT for determining optical rotations with a triplet-zeta basis set (B3 LYP/TZVP) reproduce the optical rotatory dispersions (ORD) very well for the lower members (n=4, 5) of the sigma-[n]helicenes. For the higher ones (n=7, 9, 15) the computed specific rotations turn out increasingly larger than the experimental values. The remarkable increase of the specific rotation with an increasing number of three-membered rings is proportional neither to the molecular weight nor to the number of cyclopropane rings in these sigma-[n]helicenes.     

One-electron attachment reaction of B- and Z-DNA modified by 8-bromo-2'-deoxyguanosine

The one-electron attachment reaction of 8-bromo-2'-deoxyguanosine ((Br)G) in DNA was studied by comparing that in B- and Z-DNA. Oligodeoxynucleotides (ODNs) modified by (Br)G were synthesized as Z-DNA in which the syn-conformation deoxyguanosine is stabilized by steric interference between the 8-bromo group of (Br)G and the sugar moiety. Debromination from the (Br)G-modified ODNs occurred from the one-electron attachment during the gamma-radiolysis. The structural dependence of B- and Z-DNA was observed for the one-electron attachment reaction. The conversion of (Br)G was higher in Z-DNA than in B-DNA. Because the solvent-accessible surface of the purine base in Z-DNA is greater than that in B-DNA, it is demonstrated that the reactivity of purine base C8 is enhanced in Z-DNA compared to that in B-DNA.     

Recent Progress in Chemistry of Multiple Helicenes

The last decade has witnessed multiple helicenes arising as an interesting class of nonplanar polycyclic aromatics of inherent multihelicity. These molecules present esthetic structures and interesting properties not available to helicenes of single helicity. Herein an overview of multiple helicenes with respect to structures, stereochemical dynamics, synthesis, and applications is provided. Recently reported multiple helicenes are surveyed with an emphasis on molecular structures and stereochemistry of multiple carbohelicenes. After this survey, the synthesis of multiple helicenes through the Scholl reaction is discussed and recent applications of multiple helicenes in organic electronics are summarized. On the basis of these discussions, conclusions are reached on the current status of multiple helicenes and an outlook for this field is provided.     

Theory of helicenic hydrocarbons. Part 1: Invariants and symmetry

Helicenes form a subclass of polyhexes and correspond to hydrocarbons of considerable chemical interest. This paper is the first part of a general graph-theoretical treatment of helicenes. The invariants are studied: the relations between them, their possible values, and their upper and lower bounds in helicenes. Extremal helicenes and circular helicenes are useful definitions of subclasses of the systems under consideration. Finally an account of symmetry of helicenes is given.On leave from: Department of Mathematics, Xinjiang University, Wulumuqi Xinjiang 830046, People's Republic of China.     

One-Step Simultaneous Synthesis of Circularly Polarized Luminescent Multiple Helicenes Using a Chrysene Framework

A series of multiple helicenes was simultaneously synthesized in one step by intramolecular cyclization of a single chrysene derivative containing two 2-[(4-alkoxyphenyl)ethynyl]phenyl units accompanied by rearrangements of the aryl pendants. The electrophile-induced double cyclization with or without aryl migrations proceeded efficiently under acidic conditions to afford annulative π-extension of the chrysene units and produced quadruple (QH- 2 ), triple (TH- 2 ), and double (DH- 2 ) helicenes containing [4]- and/or [5]helicene frameworks with dynamic and/or static helicene chirality in one step. Three multiple helicenes’ structures were determined by X-ray crystallography and/or density functional theory calculations. The multiple TH- 2 and DH- 2 helicenes were separated into enantiomers because of the stable one and two [5]helicene moieties, respectively, and showed intense circular dichroism and circularly polarized luminescence. Although QH- 2 , which comprises four [4]helicene subunits, was not resolved into enantiomers, the TH- 2 enantiomers were further separated into a pair of diastereomers at low temperature resulting from their substituted [4]helicene chirality.     

Rücktitelbild: A Facile and Versatile Approach to Double N‐Heterohelicenes: Tandem Oxidative C?N Couplings of N‐Heteroacenes via Cruciform Dimers (Angew. Chem. 18/2015)

Novel double N‐hetero[5]helicenes that are composed of two nitrogen‐substituted heteropentacenes are synthesized by tandem oxidative C N couplings via the cruciform heteropentacene dimers. The developed method is very facile and enables the synthesis of a double helicene in only two steps from commercially available naphthalene derivatives. These double N‐hetero[5]helicenes have larger torsion angles in the fjord regions than typical [5]helicenes, and optical/electrochemical measurements revealed a significant increase in the electronic communication between the two heteropentacene moieties of the double helicenes compared with their cruciform dimers. The optical resolution of one of the double helicenes was successfully carried out, and their stability towards racemization was remarkably higher than those of typical [5]helicenes. The synthetic strategy proposed in this paper should be versatile and widely applicable to the preparation of double helicenes from other N‐containing π‐conjugated planar molecules.     

A Facile and Versatile Approach to Double N‐Heterohelicenes: Tandem Oxidative CN Couplings of N‐Heteroacenes via Cruciform Dimers

Novel double N‐hetero[5]helicenes that are composed of two nitrogen‐substituted heteropentacenes are synthesized by tandem oxidative C? N couplings via the cruciform heteropentacene dimers. The developed method is very facile and enables the synthesis of a double helicene in only two steps from commercially available naphthalene derivatives. These double N‐hetero[5]helicenes have larger torsion angles in the fjord regions than typical [5]helicenes, and optical/electrochemical measurements revealed a significant increase in the electronic communication between the two heteropentacene moieties of the double helicenes compared with their cruciform dimers. The optical resolution of one of the double helicenes was successfully carried out, and their stability towards racemization was remarkably higher than those of typical [5]helicenes. The synthetic strategy proposed in this paper should be versatile and widely applicable to the preparation of double helicenes from other N‐containing π‐conjugated planar molecules.     

Identification of novel ligands for the Z-DNA binding protein by structure-based virtual screening

We describe the first discovery of small molecules that bind to the Z-DNA binding domain of human ADAR1 (Adenosine Deaminase Acting on RNA 1) by structure-based virtual screening of chemical database. These molecules bind to Z-DNA binding domain to inhibit the interaction with the Z-DNA. Many viruses have Z-DNA binding proteins, which are structurally similar to Z-DNA binding domain of human ADAR1, and the ability of Z-DNA binding protein to bind the Z-DNA is essential for their pathogenicity. Therefore, the molecules identified in this study may serve as novel leads for the design of agents that inhibit biological functions of those pathogenic viruses.     

Efficient synthesis of benzo fused tetrathia[7]helicenes

An efficient route toward the synthesis of symmetrical and unsymmetrical benzo fused tetrathia[7]helicenes substituted with electron donor (ED) and electron acceptor (EA) groups is reported. A common, readily available precursor 1,2- bis-(2-thienyl)benzene was used to synthesize different helicenes through a Wittig reaction, Stille coupling, and modified oxidative photocyclization.     

Azahelicenes from the Oxidative Photocyclization of Boron Hydroxamate Complexes

Aromatic hydroxamic acids (Ar–CO–NOH–Ar′) were used as bidentate chelating ligands to generate the corresponding boron hydroxamate complexes, which were subsequently transformed into nitrogen‐containing helicenes (azahelicenes) using an oxidative photocyclization method that is frequently used for stilbene‐type (Ar–CH=CH–Ar′) precursors of carbohelicenes. The nitrogen atom of the hydroxamate linker was thus directly embedded into the helicene core without using nitrogen‐containing aromatic rings in the stilbene‐type precursors. In a batch photoreaction, aza[4]helicenes were readily and efficiently prepared, but aza[6]helicenes underwent severe decomposition upon irradiation. Alternatively, a continuous flow photoreactor was employed to furnish an amide‐type aza[6]helicene.     

Synthesis of helicenes utilizing palladium-catalyzed double C-H arylation reaction

[5]- and [6]helicenes were synthesized in moderate to good yields from Z,Z-bis(bromostilbene)s by palladium-catalyzed double C-H arylation reaction. This method can be applied to the syntheses of helicenes possessing electron-deficient substituents.     

The Preparation of Enantiopure [6]‐ and [7]Helicenes from Binaphthanol

A general and efficient synthetic methodology for the preparation of enantio‐ and diastereopure [6]‐, and [7]helicenes is developed. Commercially available chiral binaphthanols are utilized to generate the arylene‐vinylene precursors, which undergo helical folding via photocyclization to give enantio‐ and diastereopure [6]‐, and [7]helicenes. These optically pure helicenes could be easily obtained via silica gel column chromatography without the use of expensive HPLC or chiral resolution reagents. The configurations and structures of these helicenes are confirmed by CD spectra and X‐ray crystallographic analysis. This work provides a new method for preparation of enantiopure helicenes.     

Structure of a copper-mediated base pair in DNA.

Stable and selective DNA base pairing by metal coordination was recently demonstrated with nucleotides containing complementary pyridine-2,6-dicarboxylate (Dipic) and pyridine (Py) bases (Meggers, E.; Holland, P. L.; Tolman; W. B.; Romesberg, F. E.; Schultz, P. G. J. Am. Chem. Soc. 2000, 122, 10714-10715). To understand the structural consequences of introducing this novel base pair into DNA we have solved the crystal structure of a duplex containing the metallo-base pair. The structure shows that the bases pair as designed, but in a Z-DNA conformation. The structure also provides a structural explanation for the B- to Z-DNA transition in this duplex. Further solution studies demonstrate that the metallo-base pair is compatible with Z- or B-DNA conformations, depending on the duplex sequence.     

Diazadithia[7]helicenes: Synthetic Exploration,Solid‐State Structure,and Properties

Diazadithia[7]helicenes were synthesized from the readily available building block ethyl 7‐chloro‐8‐formylthieno[3,2‐f]quinoline‐2‐carboxylate by a Wittig reaction–photocyclization strategy. The helicene core was functionalized by nucleophilic aromatic substitution with a variety of nucleophiles (e.g., O‐, N‐, and C‐centered) and palladium‐catalyzed reactions such as Suzuki coupling and Buchwald–Hartwig amination. Racemization studies confirmed that the enantiopure forms of these [7]helicenes are conformationally stable compared to their lower analogues. The solid‐state structures of the novel diazadithia[7]helicenes were determined by single‐crystal X‐ray diffraction. The crystal structures of these azathia[7]helicenes show columnar stacking in antiparallel fashion. The HOMO–LUMO gaps of the new compounds were determined on the basis of electrochemical and optical measurements.     

Facile Synthesis and Chiral Resolution of Expanded Helicenes with up to 35 cata-Fused Benzene Rings**

Expanded helicenes are expected to show enhanced chiroptical properties as compared to the classical helicenes but the synthesis is very challenging. Herein, we report the facile synthesis of a series of expanded helicenes Hn (n=1–4) containing 11, 19, 27 and 35 cata-fused benzene rings through Suzuki coupling-based oligomerization followed by Bi(OTf)₃-mediated regioselective cyclization of vinyl ethers. Their structures were determined by X-ray crystallographic analysis. Enantiopure H2 , H3 , and H4 can be isolated by chiral HPLC and they all exhibit strong chiroptical responses with high absorption dissymmetry factor (|g_abs|) values (0.020 for H2 , 0.021 for H3 , and 0.021–0.024 for H4 ).