https://pubs.rsc.org/en/content/articlepdf/2019/NP/C8NP00092A

Marine natural products.

Organic molecules as well as metal complexes may exist as several geometric isomers1 which display distinct physical properties and chemical reactivities. A molecule containing two atoms (in general, two carbons) attached together by a double bond with substituents W-Z may be found as two isomeric † C.D. dedicates this review to Professor Andrée Marquet as a mark of his admiration and gratitude. * To whom correspondence should be addressed: Tel: (33) 169 08 52 25. Fax: (33) 169 08 90 71. E-mail: christophe.dugave@cea.fr. ‡ Present address: Département de Chimie, Institut de Pharmacologie, Université de Sherbrooke, 3001, 12e Avenue nord, Sherbrooke, Québec, J1H 5N4 Canada. 2475 Chem. Rev. 2003, 103, 2475−2532

Cis-trans isomerization of organic molecules and biomolecules: implications and applications.

A brief analysis is presnted of the current understanding of substituent perturbations in monosubstituted benzenes as determined by substituent induced carbon chemical shifts. A critical tabulation of the four substituent chemical shifts is given for c. 700 monosubstituted benzenes.

13C substituent effects in monosubstituted benzenes

A versatile method for the synthesis of complex, fused polycyclic aromatic systems in high chemical yield is described. Construction is achieved using a general two-step synthetic sequence. Pd-catalyzed Suzuki and Negishi type cross-coupling chemistries allow for the preparation of nonfused skeletal ring systems in yields consistently >80%. The critical ring-forming step, which generally proceeds in very high to quantitative yield, utilizes 4-alkoxyphenylethynyl groups and is induced by strong electrophiles such as trifluoroacetic acid and iodonium tetrafluoroborate. The reaction in essence produces phenanthrene moieties which are integrated into extended polycyclic aromatic structures. Fused polycyclic benzenoids as well as benzenoid/thiophene systems may be prepared utilizing this methodology. The scope of the described cross-coupling/cyclization chemistry including mechanistic insights and problematic side reactions are described.

http://web.mit.edu/tswager/Desktop/tswager/www/Papers/050-PolycyclicAromatics.pdf

Directed Electrophilic Cyclizations - Efficient Methodology for the Synthesis of Fused Polycyclic Aromatics

The principles of the theoretical calculations of the carbon atom screening constant are reviewed. The Independent Electron, SCFMO and Valence Bond formulae are briefly discussed, and the relative importance of the different terms involved in an approximate decomposition of σ13C are pointed out. The variations of the excitation energy ΔE, the mean distance between the nucleus and 2p electrons, and the electronic charges and bond orders with the structure are presented. The nature of the steric effect is also explained. In a second part the various empirical correlations which make an evaluation of δ13C from structural and physical properties possible are shown. The actual substituent parameters of the main classes of compounds are listed and worked examples given to make the use of the tables easier. The correlations between δ13C and the electronic charge, electronegativity, Hammett-Taft constants, electric field effects, geometrical parameters, spectroscopic data (electronic transitions, screening of other nuclei) and pH are also discussed with a view to appraising the carbon screening.

Theoretical and empirical calculations of the carbon chemical shift in terms of the electronic distribution in molecules

The free energies of activation for hindered rotation around the C—N bond have been determined for a series of N,N-disubstituted thioamides by means of 13C and 1H dynamic nmr.A comparison between b...

1H and 13C dynamic nuclear magnetic resonance study of hindered rotation in thiobenzoylpiperidines and thiobenzoylmorpholines. Correlation between barrier heights of amides and thioamides

This paper describes the structure determinations of two new ichthyotoxic bis-quinolizidine alkaloids from the marine sponge Petrosia seriata. The structural elucidations are mostly based on homonuclear 2D-1H NMR experiments.

/pdf/petrosin-a-and-b-two-new-bis-quinolizidine-alkaloids-from-2cfln6gssq.pdf

Petrosin‐A and ‐B, Two New Bis‐Quinolizidine Alkaloids from the Sponge Petrosia Seriata(1)

L'etude RMN 13C de composes epoxybicyclo[2.2.1]‐heptaniques fait ressortir une forte influence de l'orientation endo ou exo de l'heterocycle sur le glissement chimique du 13C pontal. La difference entre les variations de glissements chimiques en 13C et 1H montre que l'effet de courant de cycle ne peut seul rendre compte des resultats observes. Copyright © 1974 Heyden & Son Ltd.

Etude par RMN 13C de quelques époxydes exo et endo dans la série du bicyclo[2.2.1]heptane

NMR and stereochemical studies of non aromatic heterocyclic compounds—II : 13C and 31P NMR of 2-methoxy-1,3,2-dioxaphosphorinanes☆

13C n.m.r. spectra of a series of N,N‐disubstituted thioamides have been recorded and signal assignments were performed. Separate signals are observed for methylene groups fixed on the nitrogen atom. Since the carbon atom syn to the thiocarbonyl sulfur resonates at higher field than the anti carbon, the syn‐anti assignment in 1H n.m.r. is easily obtained by selective double irradiation. This method, which is rapid and reliable, affords a rather general solution to the interesting problem of resonance assignments in tertiary amides and thioamides (and in analogous molecules such as oximes and nitrosamines). Copyright © 1976 Heyden & Son Ltd.

Daniel Zimmermann

Papers

1H and 13C dynamic nuclear magnetic resonance study of hindered rotation in thiobenzoylpiperidines and thiobenzoylmorpholines. Correlation between barrier heights of amides and thioamides

Petrosin‐A and ‐B, Two New Bis‐Quinolizidine Alkaloids from the Sponge Petrosia Seriata(1)

Etude par RMN 13C de quelques époxydes exo et endo dans la série du bicyclo[2.2.1]heptane

NMR and stereochemical studies of non aromatic heterocyclic compounds—II : 13C and 31P NMR of 2-methoxy-1,3,2-dioxaphosphorinanes☆

13C n.m.r. spectra of some thiobenzamides. Correlation between 13C and 1H n.m.r. spectra and signal assignments of syn and anti CH2 groups