Dihydroaromatic Boronic Esters as Building Blocks for the Synthesis of Phenanthrenes and Phenanthridines

Synthesis and reactivity of alkynyl boron compounds

Over the last century, there have been considerable developments in organoboron chemistry due to the stability, non-toxicity, and easy commercial availability of various boronic esters. Several organoboron reagents have emerged and play an increasingly important role in everyday organic synthesis. Among them, alkynyl boron compounds have attracted significant attention due to their easy synthesis and diverse reactivity. In this review, we summarize the advancement of research on alkynyl boron compounds, highlighting their importance in the synthesis of valuable compounds.

Regio- and Diastereoselective Synthesis of Cyclohexadienylborons via an Intermolecular Diels-Alder Reaction of Alkenyl MIDA Boronates with 2-Pyrones

An efficient synthesis of highly functionalized cyclohexadienylborons via an inverse electron-demand Diels-Alder reaction/CO₂ extrusion of alkenyl MIDA boronates with 2-pyrones is outlined. By controlling the reaction temperature, the corresponding C(sp³ )-rich bicyclolactones could also be readily formed. The exo-selective reactions feature good functional-group tolerance, broad substrate scope, and excellent regio- and diastereoselectivity. Oxidation of the cyclohexadienylborons in a one-pot procedure led to the construction of aromatic boronates bearing valuable functional groups. Synthetic transformations of the C-B bond were demonstrated.

Conformationally restricted benzothienoazepine respiratory syncytial virus inhibitors: their synthesis, structural analysis and biological activities

Atropisomeric drug substances are known to have different biological properties. Compounds containing the N-benzoylbenzazepine motif have been shown to exhibit energetically restricted rotation around the Ar(CO)N axis. Herein we report, for the first time, the synthesis, physical characterisation and anti-viral profiles of a series of C-4 and C-5 methylated thieno-benzazepines. NMR analysis reveals that incorporation of a single additional substituent at either of these loci influences the conformational dynamics of the azepine ring system. In the case of the C-5 alkyl analogues, the influence of the new stereocentre is so pronounced that its absolute configuration determines which unique atropisomer is obtained following the generation of the benzazepine nucleus. Screening of the alkylated derivatives for their anti-respiratory syncytial virus (RSV) activity indicates that the desired viral pathogenicity is strongly associated with the conformation adopted by the modified tricyclic scaffolds. This is particularly evident in the case of the C-5 homologues in which one atropisomer was found to be potently active and the other essentially inert. These results provide compelling evidence that we have determined the bioactive conformation shared by RSV inhibitors that employ the thienobenazapine nucleus as their core molecular architecture. Furthermore, the understanding obtained from these studies may make it possible to design improved agents against RSV infection in the future.

Diversity-Oriented Approaches to Polycyclics and Bioinspired Molecules via the Diels-Alder Strategy: Green Chemistry, Synthetic Economy, and Beyond

We describe diverse approaches to various dienes and their utilization in the Diels-Alder reaction to produce a variety of polycycles. The dienes covered here are prepared by simple alkylation reaction or via the Claisen rearrangement or by enyne metathesis of alkyne or enyne building blocks. Here, we have also included the Diels-Alder chemistry of dendralenes, a higher analog of cross-conjugated dienes. The present article is inclusive of o-xylylene derivatives that are generated in situ starting with benzosultine or benzosulfone derivatives. The Diels-Alder reaction of these dienes with various dienophiles gave diverse polycyclic systems and biologically important targets.

Comprehensive profiling of coal tar and crude oil to obtain mass spectra and retention indices for alkylated PAH shows why current methods err

Investigators use C(1) to C(4) substituted polycyclic aromatic hydrocarbons (PAH) to assess ecological risk and to track fossil fuels and related pollutants in the environment. To quantify these compounds gas chromatography/mass spectrometry (GC/MS) is used. This work demonstrates single ion monitoring (SIM) or extraction (SIE) of full scan data produces inaccurate and imprecise concentration estimates due to incorrect homologue peak assignments. Profiling of coal tar and crude oil by automated sequential GC-GC/MS provided the retention windows and spectral patterns for each homologue to correctly quantify these compounds. Simultaneous pulsed flame photometric (sulfur-specific) detection differentiated PAH from polycyclic aromatic sulfur heterocycles and their alkylated homologues when they eluted within the same retention windows and had common ions. Differences between SIE and spectral deconvolution of GC/MS data based on multiple fragmentation patterns per homologue ranged from a few percent for C(1) compounds to hundreds of percent for the higher alkylated homologues. Findings show current methods produce poor quality data adversely affecting forensic investigations, risk assessments, and weathering studies.

Synthesis of 9-fluorenylidenes and 9,10-phenanthrenes through palladium-catalyzed aryne annulation by o-halostyrenes and o-halo allylic benzenes

A number of functionally substituted 9-fluorenylidenes and 9,10-phenanthrenes have been synthesized from substituted o-halostyrenes and o-halo allylic benzenes respectively in good yields by the palladium-catalyzed annulation of arynes. The methodology tolerates a variety of functional groups, including cyano, ester, aldehyde, and ketone groups, occurs under relatively mild reaction conditions, and involves the generation of two new carbon-carbon bonds, thus providing these important carbocyclic ring systems in a single synthetic step.

An alkynylboronic ester cycloaddition route to functionalised aromatic boronic esters

A series of functionalised aromatic boronic esters have been prepared via the regioselective cycloaddition of 2-pyrones with alkynylboronates.

A novel approach to functionalised pyridazinone arrays

A series of 3,6-dichloro-1H-pyridazin-4-ones have been prepared via the cycloaddition of 3,6-dichlorotetrazine with alkynylboronates, and their employment as useful synthetic intermediates was highlighted through a selection of highly regioselective C-O, C-S and C-C bond forming reactions.