取代基对苯腈类低聚物几何及电子特征的影响

用半经验量化计算研究了一系列苯腈类低聚合物的几何结构及其电子特征。苯腈类低聚合物几何结构的计算采用半经验量子化学计算和分子力学构象分析相结合的方法,而电子特征则的计算采用ＺＩＮＤＯ／Ｓ－ＣＩ方法。取代基包括甲氧基、甲基、羟基、氨基、氟和硝基。它们在苯环上可以采用邻位、间位和对位三个取代位置。计算结果表明,不同的基团在苯环上采用不同的取代位置时,低聚物的构象会存在一定的差别,而且电性会随着基团的得失     

Synthesis of 3-amino-1,2,4-benzothiadi- azine 1,1-dioxides via a tandem aza-Wittig/heterocumulene annulation

[reaction: see text] Reaction of o-azidobenzenesulfonamides with polymer-supported triphenylphosphine affords the corresponding iminophosphoranes. Subsequent reaction with isocyanates gives 3-amino-1,2,4-benzothiadiazine 1,1-dioxides in high yields and purities. The reaction has been successfully applied to the synthesis of derivatives with various substituents at the 2- and 3-positions and in the benzenoid ring.     

Regioselective Synthesis of 1,2,3,4-Tetrasubstituted Arenes by Vicinal Functionalization of Arynes Derived from Aryl(Mes)iodonium Salts**

Herein, the synthesis of 1,2,3,4-tetrasubstituted benzenoid rings, motifs found in pharmaceutical, agrochemical, and natural products, is described.^[1] In the past, the regioselective syntheses of such compounds have been a significant challenge. This work reports a method using substituted arynes derived from aryl(Mes)iodonium salts to access a range of densely functionalized 1,2,3,4-tetrasubstituted benzenoid rings. Significantly, it was found that halide substituents are compatible under these conditions, enabling post-synthetic elaboration via palladium-catalyzed coupling. This concise strategy is predicated on two regioselective events: 1) ortho- deprotonation of aryl(Mes)iodonium salts to generate a substituted aryne intermediate, and 2) regioselective trapping of said arynes, thereby improving previously reported reaction conditions to generate arynes at room temperature and in shorter reaction times. Density functional theory (DFT) computations and linear free energy relationship (LFER) analysis suggest the regioselectivity of deprotonation is influenced by both proximal and distal ring substituents on the aryne precursor. A competition experiment further reveals the role of arene substituents on relative reactivity of aryl(Mes)iodoniums as aryne precursors.     

Benzenoid rings resonance energies and local aromaticity of benzenoid hydrocarbons

In this article, we consider partitioning of the analytical expression for resonance energy (RE) in smaller benzenoid hydrocarbons, to individual benzenoid rings of polycyclic molecules. The analytical expression for molecular RE, available since 1976, is given by the count of all linearly independent conjugated circuit in all Kekulé structures in a molecule. Analytical expression for local ring RE (RRE) is given by counting all linearly independent conjugated circuits involving single benzenoid ring in all Kekulé structures, which when added, gives the molecular RE. If for benzene ring the RRE is taken to be 1.000, rings in polycyclic benzenoid hydrocarbons have their ring RRE, which give the degree of their local aromaticity, smaller than 1.000. The difference to 1.000 is a measure of the similarity of a ring to benzene in this one-dimensional (1-D) representation of local aromaticities of benzenoid hydrocarbons. The plot of RRE against the distance of the same ring from benzene in the Local Aromaticity Map, in which benzenoid rings are characterized ring bond orders and average variations of adjacent CC bonds, shows linear correlation (with r = 0.91), reducing the local aromaticity in benzenoid hydrocarbons to 1-D molecular property. © 2018 Wiley Periodicals, Inc.     

Synthesis of polycyclic benzofused nitrogen heterocycles via a tandem ynamide benzannulation/ring-closing metathesis strategy. Application in a formal total synthesis of (+)-FR900482

A two-stage "tandem strategy" for the synthesis of benzofused nitrogen heterocycles is described that is particularly useful for the construction of systems with a high level of substitution on the benzenoid ring. The first stage in the strategy involves a benzannulation based on the reaction of cyclobutenones with ynamides. This cascade process proceeds via a sequence of four pericyclic reactions and furnishes a multiply substituted aniline derivative which can bear a variety of functionalized substituents at the position ortho to the nitrogen. In the second stage of the tandem strategy, ring-closing metathesis generates the nitrogen heterocyclic ring. This two-step sequence provides efficient access to highly substituted dihydroquinolines, benzazepines, benzazocines, and related benzofused nitrogen heterocyclic systems. The application of this chemistry in a concise formal total synthesis of the anticancer agents (+)-FR900482 and (+)-FR66979 is described.     

Asymmetric annellation effects—II

The comparison of the U.V. absorption spectra of acenes, 1:2–3:4-dibenzacenes and tetrabenzacenes shows a strong asymmetric annellation effect. This is explained on the basic assumption that an aromatic sextet or benzenoid ring can transfer only two electrons to another ring. Three benzenoid rings can thus produce an induced aromatic sextet in an included ring of the type of the central ring in triphenylene.

The synthesis of tetrabenzotetracene is described.     

Direct synthesis of 2,4-diaminoquinazolines from 2-fluorobenzonitriles

In a search for new methods for preparing 2,4-diaminoquinazolines having a diversity of substituents in the benzenoid ring, it was found that the reaction of 2,6-difluorobenzonitrile with guanidine carbonate gave 2,4-diamino-5-fluoroquinazoline in excellent yield. Extension of this approach to other 2-fluorobenzonitriles, some of which were elaborated for the first time, showed that this reaction possesses considerable generality. The cyclization was successful even when electron donating groups were present at position six. Only in two cases where a primary or secondary amino group was also present ortho to the cyano group was this transformation unsuccessful.     

The mass spectra of some alkyl and aryl oxazoles

The mass spectra of a variety of alkyl and aryl oxazoles have been determined and the spectra analyzed with the aid of deuterium labelling and high resolution mass spectrometry. In contrast to the corresponding benzenoid compounds, the mass spectra of isomeric alkyl oxazoles are distinctive and in this respect are akin to those of the corresponding pyridines. Further analogy to the pyridines is suggested by the unfavorable nature of a carbonium ion adjacent to the 2-position and this effect may be used to locate alkyl substituents attached to the oxazole nucleus. The loss of carbon monoxide from the molecular ions of 2,5-disubstituted oxazoles probably occurs with ring opening and migration of the C-5 substituent (e.g.Br) to the C-4 position.     

5H-oxazol-4-ones as building blocks for asymmetric synthesis of alpha-hydroxycarboxylic acid derivatives

5H-Alkyl-2-phenyl-oxazol-4-ones, a little-known heterocyclic ring system, are readily available via a microwave-assisted, sodium fluoride catalyst cyclization of mono-alpha-haloimides, which in turn are accessed by N-acylation of benzamides with alpha-bromo acid halides. Terminally substituted allyl systems serve as excellent substrates for Mo-catalyzed asymmetric allylic alkylation. The resultant products are formed with excellent ees involving a catalyst derived from N,N'-bis-picolinamide of trans-1,2-diaminocyclohexane and cycloheptatriene molybdenum tris(carbonyl). In addition to benzenoid, nonbenzenoid aromatic and vinyl substituents on the allyl carbonate moiety provide good to excellent regio- and diastereoselectivity as well as excellent enantioselectivity. Substituents on the heterocycle include methyl, n-butyl, allyl, isobutyl, isopropyl, and cyclohexyl. The presence of a double bond in the product allows them to be further modified via the chemistry of the double-bond, including metathesis. The products are hydrolyzed under basic conditions to provide alpha-hydroxyamides.     

Partitioning of pi-electrons in rings of polycyclic benzenoid hydrocarbons. 2.1. Catacondensed coronoids

Various types of coronoids are examined for finding the partitioning of pi-electrons in individual benzenoid rings of polycyclic aromatic hydrocarbons. A class of catacondensed coronoids, namely fibonacenes, has four pi-electrons in every ring. Most other catacondensed coronoids have more than one type of benzenoid ring, each type with a different partition, but the average per ring is always four pi-electrons. For the class of catacondensed coronoids that have an acenic hole, simple quadratic equations in terms of their number R of rings exist for the partitions of pi-electrons in the three possible ring types.     

Studies on 2,1-benzisoxazoles. Behaviour towards electrophilic substitution and cycloaddition reactions

The behaviour of 2,1-benzisoxazoles (anthranils) towards electrophilic substitutions has been studied. Nitration of 5-chloro-2,1-benzisoxazole (VII) exclusively gives 4-nitro-5-chloro-2,1-benzisoxazole (XII). However, 5-chloro-3-phenyl-2,1-benzisoxazole (VIII) gives dinitrated products XIII, one nitro group entering at position C₇ instead of C₄ of the carbocyclic ring and the other at the 4′ position of the 3-aryl ring. When 6-nitro-3-carbalkoxy-2,1-benzisoxazoles (X and XI) are nitrated, 4-nitroisomers XV and XVI are obtained exclusively. The substituents already present in the carbocyclic ring exert decisive directing influence. While the parent 2,1-benzisoxazole (Ia) fails to react with dimethyl acetylenedicarboxylate, 6-nitro-2,1-benzisoxazole (XVII) and 5-chloro-2,1-benzisoxazole (VII) react to give 1,4-cycloadducts XIX and XX, respectively. These results suggest that 2,1-benzisoxazoles possess benzenoid as well as ortho-quinonoid character.     

On the role of substituent in noncovalent functionalization of graphene and organophosphor recognition: IQA and SAPT perspective

Despite importance of integrating organic molecules with graphene to fabricate graphene‐based electronic devices, the role of substituents and interface stabilizing forces are poorly understood. In this work, the interactions of 7,7,8,8‐tetracyanoquinodimethane (TCNQ), 2,3,5,6‐tetrafluoro‐7,7,8,8‐tetracyanoquinodimethane (F4TCNQ), hydroquinone (Q), and tetrafluorohydroquinone (TFQ) with graphene have been investigated by means of interacting quantum atoms and SAPT(DFT). In addition, in context of potential design of a graphene‐based sensor for detection of the nerve agent sarin, we studied the interaction of graphene and the organic molecules with the dimethyl methylphosphonate (DMMP)—the molecule that mimics sarin. The results show that the organic molecules attach to graphene via C(sp²)?C(sp²), C(sp²)?C(sp) and H?π bonds. In addition, they trap DMMP via various linkages such as hydrogen, lonepair?π and H?π . The quantum effects play a significant role. The Pauli repulsion is responsible for p‐doping of graphene. The substituents are stabilized on graphene by the exchange‐correlation energy. The fluorination of the benzenoid ring raises the electron‐sharing . The through space and through bond effects of the fluorine atoms (‐F) increase the classical attraction of the cyano groups and benzenoid ring with graphene, respectively. When comparing performance of the ab initio and DFT methods, MP2 predicts too much attraction due to well‐known overestimation of the dispersion energy by the uncoupled dispersion component for benzene rings, while ω B97xD functional and SAPT(DFT) provide weaker interaction energies, in good agreement with each other.     

π‐Electron currents in larger fully aromatic benzenoids

Recently, we have reported on calculation of π‐electron ring currents in several smaller fully benzenoid hydrocarbons having up to eight fused benzene rings and five Clar π‐aromatic sextets. In contrast to early HMO ring current calculations and more recent ab initio calculations of π‐electron density, our current calculations are based on a graph theoretical model in which contributions to ring currents comes from currents associated with individual conjugated circuits. In this contribution, we consider several larger fully benzenoid hydrocarbons having from 9 to 13 fused rings and from six or seven π‐aromatic sextets. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

A Versatile Procedure for the Preparation of Aryl Thiocyanates Using N-Thiocyanatosuccinimide (NTS)

A mild procedure for the thiocyanation of several types of arene substrate using N-thiocyanatosuccinimide (NTS) is described. The method appears generally applicable to benzenoid substrates with a wide range of substituents, as well as to heteroaromatic analogues such as indoles and thiophenes.     

Ring signatures for benzenoids with up to seven rings,Part 1: Catacondensed systems

We revisited the π‐electron ring partitions in catacondensed benzenoids and re‐examined structural regularities reported for the ring partitions in these compounds, seeking the origin of the observed regularities. We examined the distribution of the π‐electron ring partitions by counting the contributions arising from benzene rings having different assigned numbers of π‐electrons. This has led to a better insight into the underlying structure of the π‐electron ring partitions and also to a novel and unique π‐electron “signature” of individual rings in benzenoid hydrocarbons. The physical interpretation of the local π‐electron ring partition represents the local π‐electron density of benzenoid molecules, and is not an alternative index of local aromaticity as one may erroneously assume. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008     

Analytical expressions for the count of LM-conjugated circuits of benzenoid hydrocarbons

A recursive method for enumeration of linearly independent and minimal conjugated circuits of benzenoid hydrocarbons had previously been given which is valid for several classes of benzenoid hydrocarbons. In the present article, the properties and constructions of unique minimal conjugated circuits and pairs of minimal conjugated circuits of a ring s in a benzenoid hydrocarbon B are investigated. An analytical expression for the count of LM-conjugated circuits of B is given which is based on the counts of Kekulé structures of selected subgraphs of B. By using the method, the LMC expression of any benzenoid hydrocarbon can be obtained. © 1996 John Wiley & Sons, Inc.     

π-Electron currents in fixed π-sextet aromatic benzenoids

In view of different patterns of π-electron density currents in benzenoid aromatic compounds it is of interest to investigate the pattern of ring currents in various classes of compounds. Recently such a study using a graph theoretical approach to calculating CC bond currents was reported for fully benzenoid hydrocarbons, that is, benzenoid hydrocarbons which have either π-sextets rings or “empty” rings in the terminology of Clar. In this contribution we consider π-electron currents in benzenoid hydrocarbons which have π-electron sextets and C=C bonds fully fixed. Our approach assumes that currents arise from contributions of individual conjugated circuits within the set of Kekulé valence structures of these molecules.     

Graph theoretical characterization and computer generation of certain carcinogenic benzenoid hydrocarbons and identification of bay regions

An algorithm is developed for generating and characterizing carcinogenic catacondensed benzenoid hydrocarbons. The bay regions in these structures are identified by a technique that we developed at Johns Hopkins. Using the three-digit code proposed by Balaban, and the concept of ring adjacency matrix expounded here, we generate catacondensed benzenoid hydrocarbons in the computer and identify the number of potentially carcinogenic bay regions in each of them. The results of computer generation agree with the combinatorial enumeration of Harary and Read. All structures containing up to five rings and some with six rings and the number of bay regions in these are presented. Computer results for the structures and bay regions of all seven-, eight-, and nine-membered unbranched catacondensed benzenoid hydrocarbons and the number of bays are available from the authors.