Small-angle light scattering from hedrites,ovoids, and spiral ovoids. II. Experimental

Procedures for obtaining hedrites, ovoids, and spiral ovoids in polyoxymethylene are described. Results of morphological studies on these structures by optical and electron microscopy are presented. Small-angle light scattering studies on single isolated supermolecular structures are described. The V_v and H_v diffraction patterns obtained experimentally are discussed in the light of theoretical results of Part I of this study.     

The mass spectra of small-ring heterocycles. IV

Both the high and low resolution mass spectra of fourteen isomeric trans- and cis-aroylaziridines are presented. In contrast to earlier low resolution mass spectral work on these compounds [1], a new fragmentation pathway for the loss of hydroxyl is presented. Also, the simple fission of the N-alkylnitrogen bond is described. Detailed fragmentation mechanisms are presented and discussed for the major ions found in the mass spectra.     

The scattering of light from thin polymer films: Multiple scattering. II. Effect of depolarization

A procedure is described to include the effect of depolarization of the originally plane-polarized incident light beam as it passes through a thin polymer sample on the intensity of multiple light scattering. The multiple scattering gives rise to “polarization scrambling” in which, for example, H_v scattering measurements involve multiple scattered rays which may have undergone some V_v scattering. These phenomena reduce the angular dependence of scattering since large intensities originally occurring at small values of θ are rescattered so as to enhance intensities at other angles. Correction factors for both H_v and V_v scattering are presented.     

1,8-Naphthyridines. Part I. Synthesis of some trifluoromethyl-1,8-naphthyridine derivatives

The synthesis of some 2-amino-1,8-naphthyridine derivatives substituted in the 5- and/or 7-positions with trifluoromethyl is described along with their conversions to the corresponding 1,8-naphthyridin-2(1H)ones. A modified procedure for oxidizing electron-deficient heterocyclic compounds to their N-oxides is presented.     

1,8-Naphthyridines. Part III. Synthesis of some 6-substituted-1,8-naphthyridin-2(1H)ones

The syntheses of some 1,8-naphthyridines substituted in the 6-position with heterocyclic groups are described. A synthetic route to 6-amino-5,7-dimethyl-1,8-naphthyridin-2(1H)one is also presented.     

Anionic Synthesis of Heteroarm,Star-Branched Polymers. Scope and Limitations

Abstract

The scope and limitations of the following methods for the synthesis of heteroarm star-branched polymers are presented: (a) divinylbenzene linking reactions; (b) coupling reactions with macromolecular silyl halides; and (c) 1,1-diphenylethylene-based living linking reactions. The methodology of using l, 3-bis(1-phenylethenyl)benzene to prepare A₂B₂ hetero 4-armed stars is reviewed, and the synthesis of well-defined (polystyrene)₂(1,4-polybutadiene)₂ heteroarm stars is described. The synthesis of well-defined ABC heteroarm star polymers using macromonomers functionalized with 1, 1-diphenylethylene groups is described.     

Ozonolyse von Enolethern. 10. Mitteilung

Ozonolysis of Enol Ethers. Part 10. Ozonization of Enol Ethers from 1,2‐ and 1,3‐Dicarbonyl Compounds: Direct Quantitative Synthesis of Phthalonic Acid Anhydride The results of ozonolyses of enol ethers from 1,2‐ and 1,3‐dicarbonyl compounds presented here strongly indicate that these reactions do not proceed via the established Criegee ozonolysis mechanism for nucleophilic C?C bonds. The quantitative one‐step synthesis of phthalonic acid anhydride via ozonolysis of 2‐(methoxymethyliden)‐1H‐inden‐1,3(2H)‐dione ( 28a ) is described. Furthermore, a revision of the theory of alkene ozonolysis in the presence of tetracyanoethylene (TCNE) is proposed on the basis of a single‐electron‐transfer (SET) chemistry.     

Modeling and Graphic Presentation of Acid–Base Titration Curves. Presentation of an Alternative Method

Titration curves for the acid—base–titration of polyvalent acids and bases and their mixtures can be created in a simple way and presented graphically. The method, an alternative to the existing procedures, shall be presented here for discussion. With the described method it is possible in an easy manner and for didactic purposes to show how the boundary conditions, such as concentrations, pK_a values, K_w values (temperature–dependent), and mixing ratios influence the shape of titration curves.The method comes from closed mathematical formulas, which can be developed in the form: titration degree, T = f(pH). An increase in the titration volume is, therefore, not considered. It can be neglected in practice by choice of suitable volumes and concentrations. The graphic presentation can be realized with the help of a customary mathematic program, such as MathCAD 7. The titration curves are derived in the familiar form of pH = f(T). During the derivation of the equations for the titration of polyvalent acids and bases, difficult expressions appear and approximations are suggested with only small deviations from the exact formulas, which nevertheless are both simple and manageable.The procedure is presented in a series of practical examples where computed and measured titration curves are compared. When using polyvalent acids, such as malonic acid or citric acid, the appropriate activity coefficients have to be considered. If the ionic strength is constant, which can be accomplished by addition of electrolytes like KCl, this is easily accomplished and is demonstrated by examples.     

Azadiene diels-alder reactions: Scope and applications. Total synthesis of natural and Ent-fredericamycin A

A review of our studies of the inverse electron demand Diels-Alder reactions of heteroaromatic and acyclic azadienes is presented and the application of a N-sulfonyl-1-aza-1,3-butadiene [4+2] cycloaddition reaction in the total synthesis of natural and ent-fredericamycin A is described in detail.     

Macrocyclic Spermine Alkaloids from Verbascum: Isolation,Structure Elucidation,and Syntheses of the (E/Z)-Isomeric Pairs (S)-Verbasikrine/(S)-Isoverbasikrine and (S)-Verbamekrine/(S)-Isoverbamekrine

The isolation and structure elucidation of the 17-membered macrocyclic spermine alkaloids (S)-verbasikrine ( 3 ), (S)-isoverbasikrine ( 6 ), (S)-verbamekrine ( 9 ), and (S)-isoverbamekrine ( 12 ) is presented. The syntheses of their racemates are described. The HPLC/APCI-MS analysis of the original total alkaloid extract of Verbascum pseudonobile is presented.     

Iridium‐Catalyzed C?H Activation versus Directed ortho Metalation: Complementary Borylation of Aromatics and Heteroaromatics

Systematic studies are presented demonstrating the complementarity of directed ortho metalation (DoM) and Ir‐catalyzed strategies for the provision of borylated aromatics and their subsequent Suzuki–Miyaura coupling reactions. A new concept, the use of the TMS group, readily introduced by DoM, as a latent regiodirective moiety to overcome the otherwise problematic production of isomeric borylated product mixtures is presented. Additional electrophile‐induced ipso‐deborylation and DoM reactions of the Bpin products are described.     

Synthese der diastereomeren 4-Amino- und 4-Hydroxy-3-(p-chlorphenyl)-valeriansäuren. Kristallstruktur von cis-4-(p-bromphenyl)-5-methyl-2-pyrrolidinon

Synthesis of 4-amino- and 4-hydroxy-3-(p-chlorophenyl)-valeric acids. X-ray structure of cis-4-(p-bromophenyl)-5-methyl-2-pyrrolidinone The syntheses of diastereomeric 4-amino- and 4-hydroxy-3-(p-chlorophenyl)-valeric acids and of their ring closure products (lactones and lactams), starting from 3-(p-chlorophenyl)-4-oxo-valeric acid, are described. A single-crystal X-ray structure analysis of cis-4-(p-bromophenyl)-5-methyl-2-pyrrolidinone is given. Some aspects of the biochemistry of threo-3-(p-chlorophenyl)-4-amino-valeric acid are presented.     

Front Cover: A Highly Sterically Congested Bis-Zinc-Porphyrin Containing a Single Buta-1,3-diyne Linkage: From a Serendipitous Finding to Supramolecular Encapsulation (Eur. J. Org. Chem. 35/2023)

A unique example of a bis-zinc-porphyrin chemical system in which both macrocycles are covalently connected with a single, short buta-1,3-diyne linkage placed at the ortho sites of the meso phenyl rings is presented. This dimeric compound resulted from an homo-coupling side-reaction taking place during a copper-catalyzed click reaction between an alkyne porphyrin and 2-azidopyridine derivatives. Its unexpected formation was rationalized by control experiments and an improved synthesis was achieved under copper-catalyzed Glaser-Hay coupling reaction conditions. This highly sterically congested bis-zinc-porphyrin derivative behaved as a supramolecular host for encapsulating ditopic molecular guests such as 1,4-diazabicyclo[2.2.2]octane (DABCO) with association constant K_1.1 in the order of 10⁶ M⁻¹. This value is comparable to current systems that typically feature several connecting linkages between the two zinc-porphyrin sites resulting in (supra)molecular cages ensuring a high pre-organization. As such, the requirements to take benefit from supramolecular encapsulation can be reduced to a highly rigid, minimal covalent linkage of four atoms between zinc-porphyrins as herein described.     

Improved Synthesis of Oligodeoxyribonucleotides by Solid-Phase Phosphotriester Method Utilizing O6-[2-(p-Nitrophenyl)ethyl]-2′-deoxyguanosine Derivatives

The synthesis of oligodeoxyribonucleotides on a cross-linked polystyrene solid support utilizing stable mono- and dinucleotide phosphotriester building blocks is presented. The use of O⁶[2-(p-nitrophenyl)ethyl]-2′-deoxyguanosine derivatives yields cleaner DNA fragments by suppressing side reactions. Modifications improving the phosphotriester methodology are presented. The purification methods and analysis of synthetic oligodeoxyribonucleotides are described.     

The BERKELEY system. III. General configuration-interaction methods for open-shell molecular electronic states

A system of general “open-ended” configuration-interaction (CI ) programs, specifically designed for the Harris Corporation Slash Four minicomputer, is described. These methods are general in the sense that an arbitrary list of configurations (linear combinations of Slater determinants) may be used, and open ended in that peripheral (i.e., disk) storage capacity determines the maximum size problem that can be solved. The largest variational calculations carried out to date using BERKELEY involve 7064 open-shell singlet configurations (31,898 Slater determinants). Detailed timing breakdowns are presented for four test cases, two of which involve the lowest ππ* singlet state of ethylene. The other two examples are the orthogonal or bisected singlet state of trimethylenemethane and the ⁸B₁ state of the MnCH₂ complex. In the latter case, it is found that the predicted Mn? CH₂ dissociation energy is only slightly increased by electron correlation effects.     

The thermal decomposition of hydrocarbons. Part 3. Polycyclic n-alkylaromatic compounds

The pyrolysis of the polycyclic n-alkylaromatic compounds, n-alkylpyrenes, methyl-anthracenes and n-alkylnaphthalenes is reviewed. The types and distributions of the decomposition products and also the mechanisms proposed for their formation are described. The theoretical calculations published on the feasibility of the unique elementary hydrogen transfer step, radical hydrogen transfer, are also discussed.     

Synthesis of insect trail pheromones: The isomeric 3-butyl-5-methyloctahydroindolizines

The syntheses of the geometrical isomers of 3-butyl-5-methyloctahydroindolizine are described. These compounds, reported as trail pheromones of Pharaoh ants, Monomorium pharaonis (L.), cannot be distinguished from each other by physical data alone and assignments must therefore be based on unambiguous synthesis. Routes to these compounds via suitably constituted dialkylpiperidines and a sequence involving a dialkylpyrrole are described. Infrared and nmr spectral data are presented. These data are examined for their potential in conformaational analyses of these compounds.     

Synthetische Juvenilhormone 1. Mitteilung. p-Substituierte β-Methyl-Zimtsäurederivate

In the first communication the synthetic methods are described for preparing aromatic analogues of juvenile hormone like activity. The para-substituted 2-methyl-cinnamic acid derivatives are formed by a Friedel-Crafts acylation of a phenol, followed by the Wadsworth-Emmons (Wittig-Horner)-Reaction with the corresponding phosphonates. More than 120 compounds are listed.     

A Stereocontrolied Entry to Racemic Eremophilane and Valencane Sesquiterpenes via an Intramolecular Diels-Alder Reaction

A stereocontrolied route to racemic eremophilane and valencane sesquiterpenes is described via a common intermediate 15 , accessible from an intramolecular Diels-Alder reaction. ¹³ C - NMR .-shift assignments of the bicyclic intermediates and products are presented.     

Spectra–structure relationships in carbon-13 nuclear magnetic resonance spectroscopy. Results from a large data base

A link between a substructure searching system and a ¹³C NMR data base has been established and permits the retrieval and examination of the chemical shifts associated with specific substructures. The means by which these searches are accomplished is described and the results from the searches are presented and discussed. The system is interactive, and can be used to locate in the data base the chemical shifts of carbon atoms in precisely defined environments. Alternatively, it may be used to learn the range of the chemical shifts possessed by particular types of carbon atoms, such as N-methyl or O-methyl carbons.