Annulation

About: Annulation is a research topic. Over the lifetime, 10152 publications have been published within this topic receiving 189701 citations.

Gold-Catalyzed Regiospecific C−H Annulation of o-Ethynylbiaryls with Anthranils: π-Extension by Ring-Expansion En Route to N-Doped PAHs

Abstract: We describe a novel, short, and flexible approach to diverse N-doped polycyclic aromatic hydrocarbons (PAHs) through gold-catalyzed π-extension of anthranils with o-ethynylbiaryls as reagents. This strategy uses easily accessible starting materials, is simple due to high step and atom economy, and shows good functional-group compatibility as well as scale-up potential. Mechanistically, the tandem reaction is proposed to involve a nucleophilic addition/ring opening/regiospecific C-H annulation/protodeauration sequence terminated by a Friedel-Crafts-type cyclization. Photophysical studies of the products indicated violet-blue fluorescence emission with quantum yields up to 0.45.

Utilization of the Intramolecular Cycloaddition-Cationic pi-Cyclization of an Isomünchnone Derivative for the Synthesis of (+/-)-Lycopodine

Abstract: A new annulation sequence leading to the tetracyclic skeleton of the Lycopodium family of alkaloids is effected by using the tandem cycloaddition-cationic pi-cyclization reaction of an isomunchnone dipole as the key strategic element. Synthesis of the required alpha-diazo imide precursor involved treating 5-methylcyclohex-2-en-1-one with the organocopper reagent derived from 3-methoxybenzyl chloride in the presence of chlorotrimethylsilane. Ozonolysis of the resulting silyl enol ether followed by a Wittig reaction and conversion to the desired alpha-diazo imide was carried out using standard malonylacylation and diazotization procedures. Treatment of the alpha-diazo imide with rhodium(II) perfluorobutyrate afforded a transient 1,3-dipole which subsequently cycloadded across the tethered pi-bond. The resulting cycloadduct was treated with BF(3).2AcOH to give a rearranged tetracyclic compound derived from a Pictet-Spengler-type cyclization of an N-acyliminium ion. The rearranged product was subsequently converted into a key intermediate previously used for the synthesis of (+/-)-lycopodine.

Gold(III)‐Catalyzed Site‐Selective and Divergent Synthesis of 2‐Aminopyrroles and Quinoline‐Based Polyazaheterocycles

Abstract: A facile, site-selective, and divergent approach to construct 2-aminopyrroles and quinoline-fused polyazaheterocycles enabled by a simple gold(III) catalyst from ynamides and anthranils under mild reaction conditions is described. This one-pot strategy uses readily available starting materials, proceeds in a highly step- and atom-economical manner, with broad substrate scope and scale-up potential. The key element for success in this tandem reaction is a catalyst-directed preferred quenching of the in situ generated gold carbene intermediates by a nucleophilic benzyl/2-furylmethyl moiety on the ynamides as an alternative to the known C-H annulation leading to indoles.

Synthesis of Functionalizable Boron‐Containing π‐Electron Materials that Incorporate Formally Aromatic Fused Borepin Rings

Abstract: Boron-containing p-electron systems have emerged as exciting subjects in contemporary organic materials chemistry. The strong Lewis acidity of tricoordinate boron has been utilized for the detection of biologically or environmentally relevant anions. 9] Anionic and neutral boron heteroaromatic molecules are important p-donor ligands for organometallics, and the aromaticity of boroncontaining molecules has inspired substantial experimental and theoretical investigations, thus suggesting that the heteroaromaticity of boron will play will play a key role in other areas where polarization may need to distort p-electron frameworks, such as during operation in electronic devices. The vast majority of boron-based p-electron materials was built with mainchain or lateral 18, 19] tricoordinate boron substitution or from locally antiaromatic four-p-electron fragments such as the borole nucleus within 9-borafluorene. Herein, we present the syntheses and characterization of polycyclic aromatic molecules built around the neutral and formally aromatic six-p-electron borepin ring system that is structurally poised for synthetic elaboration into complex molecular structures. The dibenzo[b,f]borepin (DBB) framework continues to attract substantial attention. 22] Van Tamelen et al. reported the first isolation of DBB as its ethanolamine adduct, and Piers and co-workers very recently reported a B-mesityl DBB that slowly oxidized under ambient conditions. Theoretical studies have revealed planarity throughout the B-H DBB; thus planarity was attractive to us as a means to enhance p-electron delocalization, and nucleus-independent chemical shift (NICS) values reveal a weak degree of aromatic character within the borepin ring of benzo-annelated molecules. However, no synthetic routes for robust and stable tricoordinate borepins that could be tailored into complex p-electron systems have been reported to date. The synthesis of the parent compound DBB 1a is shown in Scheme 1. The stilbene precursor 2a was constructed by a Wittig-type process using reactants derived from a-bromo-o-