Medium‐Sized‐Ring Analogues of Dibenzodiazepines by a Conformationally Induced Smiles Ring Expansion

Analogues of dibenzodiazepines, in which the seven‐membered nitrogen heterocycle is replaced by a 9–12‐membered ring, were made by an unactivated Smiles rearrangement of five‐ to eight‐membered heterocyclic anthranilamides. The conformational preference of the tertiary amide in the starting material leads to intramolecular migration of a range of aryl rings, even those lacking electron‐withdrawing activating groups, and provides a method for n →n +4 ring expansion. The medium‐ring products adopt a chiral ground state with an intramolecular, transannular hydrogen bond. The rate of interconversion of their enantiomeric conformers depends on solvent polarity. Ring size and adjacent steric hindrance modulate this hidden hydrophilicity, thus making this scaffold a good candidate for drug development.     

The NICS‐XY‐Scan: Identification of Local and Global Ring Currents in Multi‐Ring Systems

Nucleus‐independent chemical shift (NICS)‐based methods are very popular for the determination of the induced magnetic field under an external magnetic field. These methods are used mostly (but not only) for the determination of the aromaticity and antiaromaticity of molecules and ions, both qualitatively and quantitatively. The ghost atom that serves as the NICS probe senses the induced magnetic field and reports it in the form of an NMR chemical shift. However, the source of the field cannot be determined by NICS. Thus, in a multi‐ring system that may contain more than one induced current circuit (and therefore more than one source of the induced magnetic field) the NICS value may represent the sum of many induced magnetic fields. This may lead to wrong assignments of the aromaticity (and antiaromaticity) of the systems under study. In this paper, we present a NICS‐based method for the determination of local and global ring currents in conjugated multi‐ring systems. The method involves placing the NICS probes along the X axis, and if needed, along the Y axis, at a constant height above the system under study. Following the change in the induced field along these axes allows the identification of global and local induced currents. The best NICS type to use for these scans is NICS_πZZ, but it is shown that at a height of 1.7 Å above the molecular plane, NICS_ZZ provides the same qualitative picture. This method, namely the NICS‐XY‐scan, gives information equivalent to that obtained through current density analysis methods, and in some cases, provides even more details.     

High Reactivity of Strained Seven‐Membered‐Ring trans‐Alkenes

trans‐Oxasilacycloheptenes are highly reactive strained alkenes. Competition reactions showed that these seven‐membered ring trans‐alkenes underwent [4+2] cycloaddition reactions faster than a trans‐cyclooctene. They also reacted with quinones and dimethyl acetylenedicarboxylate to form adducts with high diastereoselectivity. Kinetic studies showed that ring strain increases nucleophilicity by approximately 10⁹.     

Counter‐Rotating Spin‐Polarised Ring Currents in Odd‐Electron Carbocycles

We propose a molecular‐orbital model to explain how majority and minority spins in odd‐π‐electron carbocycles sustain counter‐rotating magnetic‐field‐induced ring currents. The model is based on the ipsocentric approach to magnetic response, in which ring currents are dominated by frontier‐orbital contributions obeying angular‐momentum selection rules. Coupled unrestricted Hartree–Fock ab initio calculations of the ring‐current responses for singly charged benzene and planarised cyclo‐octatetraene ions confirm the predictions of the qualitative model, and are consistent with correlated MP2 spin‐polarised current calculations.     

Iridium‐Catalyzed Enantioselective Synthesis of Pyrrole‐Annulated Medium‐Sized‐Ring Compounds

Enantioselective synthesis of pyrrole‐annulated medium‐sized‐ring compounds by an iridium‐catalyzed allylic dearomatization/retro‐Mannich/hydrolysis sequence is presented. Various substituted pyrrole‐annulated seven‐ and eight‐membered‐ring products were obtained under mild reaction conditions with moderate to good yields and excellent enantioselectivity. Additionally, these products contain a scaffold widely distributed in natural products and biologically active compounds. The current method provides a convenient way for accessing such pyrrole‐anuulated medium‐sized‐ring compounds.     

Ring Currents in Benzo‐ and Benzocyclobutadieno‐Annelated Biphenylene Derivatives

The effect of benzo and benzocyclobutadieno annelation on the current density induced in a series of biphenylene derivatives is examined at the B3LYP/cc‐pVDZ level of theory, by using the CTOCD‐DZ method. Angular benzo annelation increases, whereas linear benzo annelation decreases the intensity of paratropic (antiaromatic) current density along the four‐membered ring of biphenylene. The opposite effect is found for benzocyclobutadieno annelation. It is shown that the extent of local aromaticity of the four‐membered ring in biphenylene congeners can vary from highly antiaromatic to nonaromatic, as a result of different modes of annelation.     

Extension of N‐Heteroacenes through a Four‐Membered Ring

The synthesis of novel π‐extended N‐heteroacenes, which have a large tetraazaacene subunit and a quinoxaline subunit connected through a four‐membered ring, is reported. They were studied with experimental and computational methods in comparison to the corresponding tetraazaacenes. As found from the DFT calculation, the four‐membered ring is a better linker than a five‐membered ring or a C?C single bond to extend N‐heteroacenes for a new design of n‐type semiconductors in terms of the spatial delocalization and energy level of LUMO as well as the reorganization energy. In solution‐processed thin film transistors, the π‐extended N‐heteroacenes are found to function as n‐type semiconductors with field effect mobility of up to 0.02 cm² V^?1 s^?1 under ambient conditions.     

Structure and Reactivity of an Isolable Seven‐Membered‐Ring trans‐Alkene

The isolation and characterization of a trans‐oxasilacycloheptene is reported. Single‐crystal X‐ray crystallographic studies indicate a high level of strain and deviation from ideal geometry. Reactions with several electrophiles demonstrated the nucleophilicity of the C?C double bond, affording oxasilacycloheptane and tetrahydrofuran products as single diastereomers.     

Chiral Framework with 20‐Ring Channels Exhibiting Metal‐Activator‐Free Photoluminescence

The use of biomass‐derived sucrose has unprecedentedly induced the first chiral zinc phosphite structure with 20R channels along with a series of acentric frameworks, unveiling a facile synthesis of chiral nanoporous frameworks. The 20R‐channel structures are metal‐activator free but display blue‐to‐white photoluminescence under long UV excitation.     

Ligand‐Directed Divergent Synthesis of Carbo‐ and Heterocyclic Ring Systems

Chemical tools that enable a catalytic reaction to selectively and efficiently yield different products will allow charting of wider chemical space. In ligand‐directed divergent synthesis, a common mode of catalysis is modulated by employing different ligands for catalytic organometallic complexes to transform either common substrates or common reactive intermediates into distinct molecular scaffolds. The strategy has the potential to create important and diverse scaffolds and to unveil novel modes of catalytic transformations for wider synthetic applications. This strategy is described and recent efforts in this emerging field of catalysis, focusing on transition‐metal catalysis for the synthesis of carbo‐ and heterocyclic ring systems, are reviewed.     

Antimicrobial Activity of Novel Tetra‐ and Penta‐azaheterocyclic Ring Systems

A novel series of substituted [1,2,4]triazolo[4′,3′:1,2]pyrimido[4,5‐c ]benzo[f ]isoquinolin‐14(10H )‐one was synthesized from the reaction of hydrazonoyl chlorides with pyrimidine thione derivative or via oxidative cyclization of 3‐(2‐substituted‐benzylidene‐hydrazinyl)‐7,8‐dihydrobenzo[f ]pyrimido[4,5‐c ]isoquinolin‐1(2H )‐one. Also, some polyhetero‐cyclic ring systems were prepared through the reaction of 2‐dimethylaminomethylene‐3,4‐dihydro‐2H‐naphthalen‐1‐one and heterocyclic amines. The biological activity of some new products was evaluated, and the results obtained revealed that compounds 10e , 13a , and 18 showed excellent activities against the most bacteria and fungi species used.