A Review on Synthesis, Reactions and Biological Properties of Seven Membered Heterocyclic Compounds: Azepine, Azepane, Azepinone

Enantioselective Synthesis of 1-Dihydrobenzazepines through Rh2(II)-Catalyzed Cycloisomerization of 1,6-Enyne

The 1-dihydrobenzazepine skeleton has emerged as a privileged structural motif in bioactive molecules. However, due to a lack of asymmetric methodology, access to chiral 1-dihydrobenzazepines has remained limited. Herein, we report the first intermolecular asymmetric cycloisomerization of benzo-fused enynes for the synthesis of chiral 1-dihydrobenzazepines via dirhodium catalysis. This methodology features high efficiency (up to 98% yield), high enantioselectivity (up to 99% ee), and broad scope of nucleophiles, including oxygen nucleophiles (alcohols, phenols, and carboxylic acids) and carbon nucleophiles (silyl enol ethers). Theoretical and experimental mechanistic studies reveal that the reaction pathway encompasses an asymmetric cycloisomerization, which gives rise to a dirhodium carbene containing a donor-acceptor (D-A) cyclopropane moiety, followed by a ring-opening process and stereoselective nucleophilic attack by external nucleophiles on the cyclopropyl ring. Control experiments demonstrate the pivotal role of the terminal group capped on the alkynyl group of substrates in achieving good efficiency.

Dynamic Kinetic Activation of Aziridines Enables Radical-Polar Crossover (4 + 3) Cycloaddition with 1,3-Dienes

The cycloaddition of aziridines with unsaturated compounds is a valuable method for synthesizing nitrogen heterocycles. However, this process is predominantly substrate-controlled, posing significant challenges in regulating the regioselectivity of the C-N bond cleavage. In this study, we report a nickel-catalyzed dynamic kinetic activation strategy that enables catalyst-controlled activation of aziridines. Various types of aziridines, including 2-phenyl, 2-carbonyl, 2-alkyl, and disubstituted aziridines, consistently cleave their more sterically hindered C-N bonds to generate 1,3-radical anion intermediates. These intermediates participate in a highly regioselective 1,4-Heck/allylic substitution cascade with aromatic branched 1,3-dienes, resulting in a radical-polar crossover (4 + 3) cycloaddition that produces seven-membered azepine products. This approach not only complements traditional dipolar cycloaddition, in which aziridines typically act as zwitterionic 1,3-dipoles, but also introduces an unusual cycloaddition mode for 1,3-dienes. Experimental investigations and density functional theory (DFT) calculations provide insight into the reaction mechanism.

Skeletal Rearrangement of Oxazole to Azepine and Pyrrole through Dynamic 8π Electrocyclizations

We present a novel approach for the skeletal rearrangement of an oxazole into an azepine and pyrrole through a dynamic electrocyclization process, showing an innovative, unconventional reaction sequence. This method enables precise control of regioselectivity in competitive 6π and 8π electrocyclization reactions, rendering the final products rich in functional groups that can be further developed for the synthesis of nitrogen-containing scaffolds. This is an unprecedented example of the selective synthesis of seven- and five-member heterocycles via dynamic electrocyclization ring opening or closure.

Iodine(III)-Mediated Oxidation of Anilines to Construct Dibenzazepines

The development of an efficient process that produces bioactive medium-sized N-heterocyclic scaffolds from 2-substituted anilines using either iodosobenzene or (bis(trifluoroacetoxy)iodo)-benzene is reported. The tether between the sulfonamide and the aryl group can be varied to access dihydroacridine-, dibenzazepine-, or dibenzazocine scaffolds. While substitution on the aniline portion is limited to electron-neutral- or electron-poor groups, a broader range of functional groups are tolerated on the ortho-aryl substituent and site selective C-NAr bond formation can be achieved. Preliminary mechanistic investigations suggest that medium-ring formation occurs via radical reactive intermediates.

(4+3) Annulation of Donor-Acceptor Cyclopropanes and Azadienes: Highly Stereoselective Synthesis of Azepanones

Azepanes are important seven-membered heterocycles, which are present in numerous natural and synthetic compounds. However, the development of convergent synthetic methods to access them remains challenging. Herein, we report the Lewis acid catalyzed (4+3) annulative addition of aryl and amino donor-acceptor cyclopropanes with 2-aza-1,3-dienes. Densely substituted azepane derivatives were obtained in good to excellent yields and with high diastereoselectivity. The reaction occurred under mild conditions with ytterbium triflate as the catalyst. The use of copper triflate with a trisoxazoline (Tox) ligand led to an enantioselective transformation. The obtained cycloadducts were convenient substrates for a series of further modifications, showing the synthetic utility of these compounds.

Synthesis of Azepane Derivatives via Formal 1,3-Migration of Hydroxy and Acyloxy Groups and Selective Annulation

Formal 1,3-migration of hydroxy and acyloxy groups initiated by α-imino rhodium carbene was achieved, and the following selective annulations of the corresponding zwitterions could efficiently afford azepane derivatives. Benefiting from a time-saving procedure as well as a good functional group tolerance, this unique migration-annulation protocol could provide an efficient tool for synthesizing seven-membered N-heterocycles. The plausible mechanism is discussed.

Research progress on antineoplastic, antibacterial, and anti-inflammatory activities of seven-membered heterocyclic derivatives

Abstract:

Seven-membered heterocyclic compounds are important drug scaffolds, because of their unique chemical structures. They widely exist in natural products and show a variety of biological activities. They have commonly been used in central nervous system drugs in the past 30 years. In the past decade, there are many studies on the activities of antitumor, antibacterial, etc. Herein, we summarize the research advances in different kinds of seven-membered heterocyclic compounds containing nitrogen, oxygen, and sulfur heteroatoms with antitumor, antisepsis, and anti-inflammation activities in the past ten years, which is expected to be beneficial to the development and design of novel drugs for the corresponding indications.

Asymmetric three-component reaction of diazo compound with alcohol and seven-membered imine

A dirhodium and chiral phosphoric acid co-catalyzed asymmetric three-component reaction of diazo compound with alcohol and seven-membered imine has been developed via Mannich-type interception of transient oxonium ylide. This reaction...