氧杂环丁烷的扩环反应

氧杂环丁烷是一类重要的小杂环化合物,也是重要有机合成中间体,在有机化学、药物化学和高分子化学中都有广泛的应用.作为具有较大环张力的小杂环化合物,氧杂环丁烷类化合物除可以发生开环反应外,也很容易发生扩环反应,构建含氧普通环到大环化合物.主要总结了氧杂环丁烷的扩环反应,包括重氮化合物作为卡宾前体与氧杂环丁烷的扩环反应、金属...     

Stacking interactions between nitrogen-containing six-membered heterocyclic aromatic rings and substituted benzene: studies in solution and in the solid state

The stacking interactions between an aromatic ring and a pyridine or a pyrimidine ring are studied by using a series of triptycene-derived scaffolds. The indicative ratios of the syn and anti conformers were determined by variable-temperature NMR spectroscopy. The syn conformer aligns the attached aromatic ring and the heterocycle in a parallel-displaced orientation while the anti conformer sets the two rings apart from each other. Comparing to the corresponding control compounds where a benzene ring is in the position of the heterocycle, higher attractive interactions are observed as indicated by the higher syn/anti ratios. In general, the attractive interactions are much less sensitive to the substituent effects than the corresponding nonheterocycles. The greatest attractive interactions were observed between a pyrimidine ring and a N,N-dimethylaminobenzene, consistent with a predominant donor-acceptor interaction. The interactions between a pyridine ring and a substituted benzene ring show that the pyridine is comparable to that of a NO2- or a CN-substituted benzene ring except for the unpredictable substituent effects.     

A Topological Approach to the Problem of Ring Structures

In the mechanized documentation of chemical literature, the definition of structural concept is very important. The usual for definitions for ring structures are inadequate. Essential ring structures are sometimes not recognized on the basis of these definitions and are therefore missed in a literature search. This is particularly true of bridged ring systems. The ring concept and ring condensation types are now redefined on a topological basis in the closest possible analogy to the intuitive approach of the chemist. In complicated molecular structures, these “fundamental rings” can be easily determined, either manually or by means of a programmed computer. The concept of the “ring complex” is defined and suggested as a preliminary screen in literature searches for ring structures. This will save machine time, and so reduce the cost of searches.     

Satellite Hole Investigation of the Vibrational Modes of 9-Aminoacridine upon Binding to DNA

The spectral features of satellite holes are used to investigate 9-aminoacridine-DNA interactions. The hole depths of the outer ring vibronic modes are reduced more than that of the inner ring vibronic modes, implying that inner ring motion is less perturbed than outer ring motion. As a result, the mode coupling between the inner ring and outer ring is reduced upon binding to DNA. However, similar hole frequency and width of the satellite hole corresponding to the NH₂ mode upon binding to DNA imply that the amino group of 9-aminoacridine sits outside the DNA.     

Polyesters by a Radical Pathway: Rationalization of the Cyclic Ketene Acetal Efficiency

Radical ring‐opening polymerization (rROP) of cyclic ketene acetals (CKAs) combines the advantages of both ring‐opening polymerization and radical polymerization thereby allowing the robust production of polyesters coupled with the mild polymerization conditions of a radical process. rROP was recently rejuvenated by the possibility to copolymerize CKAs with classic vinyl monomers leading to the insertion of cleavable functionality into a vinyl‐based copolymer backbone and thus imparting (bio)degradability. Such materials are suitable for a large scope of applications, particularly within the biomedical field. The competition between the ring‐opening and ring‐retaining propagation routes is a major complication in the development of efficient CKA monomers, ultimately leading to the use of only four monomers that are known to completely ring‐open under all experimental conditions. In this article we investigate the radical ring‐opening polymerization of model CKA monomers and demonstrate by the combination of DFT calculations and kinetic modeling using PREDICI software that we are now able to predict in silico the ring‐opening ability of CKA monomers.     

Cyclophanes—13: Crystal and molecular structure of [2.2][2,5]furano(1,4)naphthalenophane

The crystal and molecular structure of [2.2](2,5)furano(1,4)naphthalenophane (1) was determined by X-ray crystallography. The molecule exists in the anti-conformation and the study represents the first instance in which the structural features of a naphthalenoid ring within a cyclophane were determined. Crystals of cyclophane 1 are orthorhombic, space group Pbca, with a = 7.859(2). b = 11.482(3) and c = 28.818(8) Å. While the nonbridged portion of the naphthalenoid ring is planar, the portion which is bridged to the furanoid ring through its 1 and 4 C atoms is puckered and boat-shaped. These C atoms are positioned 14° out of the plane of the other four C atoms of this ring. The furanoid ring is essentially planar but is not parallel to the naphthalenoid ring. It is inclined 22° to the least squares plane of the bridged portion of the naphthalenoid ring. This angle of inclination staggers the atoms of the furanoid and bridged naphthalenoid ring and positions the 3 and 4 C atoms, the 2 and 5 C atoms and the 0 atom of the furanoid ring 3.4. 2.9 and 2.6 Å. respectively, from the least squares plane of the bridged portion of the naphthalenoid ring. While the internal angles around the bridging C atoms α- to the naphthalenoid ring are 109°, those α- to the furanoid ring are 113°. In addition unusually large bond angles ($\text{\$}\text{?}$137°) at the 2 and 5 C atoms of the furanoid ring, external to the ring, are also observed. The distortions are considered with respect to the strain within the cyclophane macrocycle and are compared with other similar systems.     

The effect of the ferrocene unit on mesomorphic properties

The synthesis of a number of 1,1'-disubstituted ferrocene-containing compounds is described; the structures of the compounds containing the ferrocene unit are related to those of mesogenic systems containing a 1,4-disubstituted benzene ring or a trans-1,4-cyclohexyl ring. Direct comparisons are made between the aryl-, cyclohexyl- and ferrocene-containing compounds in order to assess the effect on transition temperatures of replacing a benzene or cyclohexyl ring with a ferrocene unit. In comparison with conventional ring systems the ferrocene unit causes substantial reductions in clearing temperatures.     

Synthesis of ACE tricyclic systems of daphnicyclidin A and dehy-droxymacropodumine A

The synthesis of the ACE tricyclic system of daphnicyclidin A and dehydroxymacropodumine A are developed. The key reactions include an efficient aldol reaction to introduce chiral fragment 33 for further construction of piperidine ring B and seven-membered ring C, a nucleophilic addition of lithium pentene to aldehyde for installation of ring E, and a photocatalytic decarboxylation conjugate addition to construct ring C.     

Theoretical Calculations of β-Lactam Antibiotics. Part VI. AM1 calculations of alkaline hydrolysis of clavulanic acid

The gas-phase basic hydrolysis of clavulanic acid ( a ) was studied by using the AM1 semi-empirical method. The results obtained show that the hydroxyethylidene side chain at C(2) is pivotal to the stability of the different reaction products involved. The products with an open oxazolidine ring are more stable than those with a closed ring fused to the β-lactam ring. This behaviour differs from that of penicillins and cephalosporins where the most stable degradation products are those with an intact thiazolidine or dihydrothiazine ring, respectively, fused to the β-lactam ring. The different chemical reactivity of clavulanic acid relative to penicillins and cephalosporins could explain the disparate behaviour of the latter two types of compound towards β-lactamases. Once the acyl-enzyme intermediate of clavulanic acid has been formed, it can evolve with cleavage of the oxazolidine ring to form a difficult to deacylate compound.     

Designable Aluminum Molecular Rings: Ring Expansion and Ligand Functionalization

Presented herein are the Al^III molecular ring architectures from 8‐ring to 16‐ring. Although there are numerous reported cyclic coordination compounds based on transition metals, gallium, or lanthanides, the Al versions are less developed due to the fast hydrolysis nature of Al³⁺ ion. With the assistant of monohydric alcohols, a series of atomic precisely Al molecular rings based on benzoates are synthesized. The ring expansion of these Al‐rings from 8‐ring to 16‐ring is related to the monohydric alcohol structure‐directing agents. Moreover, the organic ligands on the Al‐rings can be modified by using various benzoate derivatives, which lead to tunable surface properties of the Al‐rings from hydrophilicity to ultra‐hydrophobicity. Importantly, 4‐aminobenzoic acid bridged 16‐ring is soluble in organic solvents and exhibits high solution stability revealed by mass spectroscopy. Ligand substitution also can be performed between these Al‐rings, which reveal controllable ligand functionalization of these Al‐rings.     

Ring Expansion Strategies for the Synthesis of Medium Sized Ring and Macrocyclic Sulfonamides

Two new ring expansion strategies are reported for the synthesis of medium sized ring and macrocyclic sulfonamides. Both methods can be performed without using classical protecting groups, with the key ring expansion step initiated by nitro reduction and amine conjugate addition respectively. Each method can be used to make diversely functionalised cyclic sulfonamides in good to excellent yields, in a range of ring sizes. The ring size dependency of the synthetic reactions is in good agreement with the outcomes modelled by Density Functional Theory calculations.     

Synthesis of Thiadiazolylaminoglycosides Through Ring Contraction of Triazinoglycosides Induced by [TBA‐Ox]

A new synthetic route to thiadiazolylaminoglycosides, by a ring expansion/ring contraction sequence of glycosyl triazines, has been developed. Two potential mechanisms of this oxidative ring contraction using [TBA‐Ox] are discussed. The more plausible involves formation of an oxatriazepane intermediate followed by loss of formic acid, ring opening, and subsequent recyclization.     

Unsupervised 3D ring template searching as an ideas generator for scaffold hopping: use of the LAMDA, RigFit, and field-based similarity search (FBSS) methods

Crystal structures taken from the Cambridge Structural Database were used to build a ring scaffold database containing 19 050 3D structures, with each such scaffold then being used to generate a centroid connecting path (CCP) representation. The CCP is a novel object that connects ring centroids, ring linker atoms, and other important points on the connection path between ring centroids. Unsupervised searching in the scaffold and CCP data sets was carried out using the atom-based LAMDA and RigFit search methods and the field-based similarity search method. The performance of these methods was tested with three different ring scaffold queries. These searches demonstrated that unsupervised 3D scaffold searching methods can find not only the types of ring systems that might be retrieved in carefully defined pharmacophore searches (supervised approach) but also additional, structurally diverse ring systems that could form the starting point for lead discovery programs or other scaffold-hopping applications. Not only are the methods effective but some are sufficiently rapid to permit scaffold searching in large chemical databases on a routine basis.     

Carbon-13 NMR of fluorocyclopropanes

Carbon-13 and hydrogen NMR data are presented for several cyclopropanes with one to four fluorine atoms attached to the ring. Substituents directly attached to a ring carbon are found to unshield that carbon to an extent increasing with their electronegativity, but remote substituents may have an opposite effect. Relative orientation of the substituent groups, especially if they are bulky, also has a strong influence on the ring-carbon shifts. Chemical shifts of carbons in methyl groups attached to the ring change to an extent which is additive in the effects of gem and cis substituents. One-bond coupling of ring carbons with fluorines is affected both by geminal and vicinal substituents, in a way generally related to their electronegativity. It is tentatively concluded that two-bond coupling between ring carbons and ring-attached fluorines depends in magnitude primarily on what groups are cis to the fluorine. Two-bond coupling between a carbon atom in a ring-attached methyl and the hydrogen gem to the methyl appears to be vanishingly small, but there is appreciable three-bond coupling of the methyl carbons to vicinal hydrogens.     

Selective tandem enyne metathesis for the synthesis of functionalized cycloheptadienes

The regio- and site-selective ring expansion of dienes and the regioselective ring expansion of substituted cyclopentenes provide 1,3-cycloheptadienes by enyne metathesis under methylene-free conditions. Site-selectivity results from differential ring strain among two different cycloalkenes in diene reactants. The high regioselectivity found in the ring expansion of tetrahydroindene (THI) is explained on the basis of a selective ring opening by the second generation Grubbs' ruthenium carbene complex. The ring opening of substituted cyclopentenes and cyclopentene contained in a bicyclic ring system was also achieved. The ring expansion of bicyclic dienes provided seven-membered dienes contained in the bicyclo[5.2.0]nonane ring system. Details of the structural analysis are also discussed. A mechanistic analysis is provided to account for the data presented herein.     

9,9‐Di‐n‐octyl‐9H‐fluorene

The title compound, C₂₉H₄₂, crystallizes from the melt as a triclinic crystal. The unit cell contains three crystallographically independent mol­ecules. The three fluorene ring systems are oriented such that two non‐equivalent ring systems related by a roto‐translation are separated by a third ring system oriented orthogonally to them. The octyl chains of all three mol­ecules are perpendicular to the fluorene ring system and force a 7.4 Å separation between the two coplanar mol­ecules, thereby preventing mol­ecular π‐stacking.     

11‐Methyl‐12a‐phenyl‐9a,12a‐di­hydro­phenanthro­[9′,10:5,6][1,4]­dioxino­[2,3‐d]­thia­zole

In the title compound, C₂₄H₁₇NO₂S, the dioxine and thia­zoline rings are distorted from planarity towards a half‐chair and an envelope conformation, respectively. The configurations of the dioxine ring, the thiazoline ring and the attached phenyl ring are conditioned by the sp³ state of the two bridgehead C atoms. The phenanthrene system is nearly coplanar with the dioxine ring, while the attached phenyl ring is orthogonal to the thia­zoline ring.     

New way of describing static and dynamic deformations of the Jahn-Teller type in ring molecules

A new method is presented to describe deformations of an N-membered planar ring (N-ring) molecule in terms of deformation vectors that can be expressed by a set of 2N-3 deformation amplitudes and phase angles. The deformation coordinates are directly derived from the normal vibrational modes of the N-ring and referenced to a regular polygon (N-gon) of unit length. They extend the conceptual approach of the Cremer-Pople puckering coordinates (J. Am. Chem. Soc. 1975, 97, 1354) to the planar ring and make it possible to calculate, e.g., a planar ring of special deformation on a Jahn-Teller surface. It is demonstrated that the 2N-3 deformation parameters are perfectly suited to describe the pseudorotation of a bond through the ring as it is found in cyclic Jahn-Teller systems. In general, an N-membered planar ring can undergo N-2 different bond pseudorotations provided the energetics of such a process is feasible. The Jahn-Teller distortions observed in ring compounds correspond either directly to the basic pseudorotation modes or to linear combinations of them. Any deformed ring molecule can be characterized in terms of the new ring deformation coordinates, which help to identify specific electronic effects. The usefulness of the ring deformation coordinates is demonstrated by calculating the Jahn-Teller surfaces for bond pseudorotation in the case of the cyclopropyl radical cation and cyclobutadiene as well as the ring deformation surfaces of disulfur dinitride and its dianion employing multireference averaged quadratic coupled cluster (MR-AQCC) theory, equation-of-motion coupled cluster theory in form of EOMIP-CCSD, and single determinant coupled cluster theory in form of CCSD(T).     

STRUCTURE OF A THYMINE-THYMINE ADDUCT FORMED BY MENADIONE PHOTOSENSITIZATION

Abstract— The structure of one of the dithymine adducts formed by near-UV photosensitization of aqueous oxygenated thymine in the presence of 2-methyl- 1, 4-naphthoquinone is reported. The compound, 6'β-hydroxy-5'β-1 - [5-methylpyrimidinyl- 2,4-dione]-5'-6'-dihydrothymine has one thymine ring (ring I) linked through the 1-nitrogen atom to the C5' atom of a second thymine, which has been hydroxylated af C6' (ring II). Crystals are monoclinic, space group 12/c, and the structure was refined to R_obs= 0.036 for 2072 unique reflections with intensities I greater than 2.33(I). Ring I is planar, whereas ring II is not. Ring I and the OH group on ring II are cis to ring II. The planar ring I and the OH group are attached, respectively, in an equatorial and axial manner to ring II (which is in the sofa conformation). The planar rings I of close-lying pairs of molecules stack parallel to each other. The structure is held together by a hydrogen-bonding system consisting of the water molecules, the NH groups, two of the C=O groups and the OH group. The chemical formula and relative configurations at C5' and C6 are established by this analysis.     

百部酰胺的全合成研究进展

百部酰胺(Stemoamide)是从百部科植物对叶百部Stemona tuberosa L.根部分离得到的天然产物。百部化合物在中医药应用中具有镇咳和驱虫的功效。其结构是γ-丁内酯并氮杂薁环的三环体系,有四个连续的手性中心。文章综述了目前国内外对百部酰胺Stemoamide的全合成方法,着重从成环顺序的角度进行论述,介绍了(Diels-Alder)-(逆-Diels-Alder)策略、自由基环化、RCM环化、分子内的Barbier反应和仿生亚胺离子环化等方法在百部酰胺全合成中的应用。