Novel 3,4-Diazabenzotropone Compounds (2,3-Benzodiazepin-5-ones): Synthesis, Unique Reactivity, and Biological Evaluation

Recent advances in 8π electrocyclization reactions

Medium-ring systems, which constitute a class of structurally intriguing and biologically important molecules, are present in many natural products and pharmaceuticals. However, the construction of these skeletons tends to be difficult because of the torsional strain of the medium-sized ring, and control of the selectivity is also challenging in these flexible skeletons. Electrocyclization is one of the most straightforward methods to construct medium-sized rings and this process typically proceeds in a stereospecific manner, resulting in the stereo-controlled formation of two neighboring stereocenters. At present, there are few studies on 8π electrocyclization, mainly focusing on the synthesis of small molecules, while the applications in the synthesis of functional materials and biological contexts are rare. This feature article highlights recent advances, from 2000 to 2022, in the 8π electrocyclization reaction. This study is organized into four sections based on the size/composition of the target ring, including the synthesis of aza-seven-membered, cycloheptene, cyclooctene and bicyclo[4,2,0]octane frameworks. We expect that this feature article will provide beneficial guidance for the selective construction of medium-ring skeletons.

Facileo-quinodimethane formation from benzocyclobutenes triggered by the Staudinger reaction at ambient temperature

4π Ring-opening at ambient temperature triggered by the Staudinger reaction.

[Development of Novel Preparations for Nitrogen Heterocycles Based on Cascade Reactions]

　Nitrogen heterocycles are important skeletons in biologically active compounds such as medicines and natural alkaloids. However, in terms of the efficiency of the synthetic process, the many synthetic steps required to achieve the target compounds with complex architectures pose a significant problem. To overcome this challenge, novel approaches were developed to afford biologically active heterocycles, 1,2-diazepines, pyrroloisoquinolines, and pyrrolizidines utilizing cascade reactions that enable multiple bond formation in a one-pot process. This review discusses three one-pot reactions: 1) 1,2-diazepine synthesis from cyclobutenones and lithiodiazoesters via cascade 4π-8π electrocyclization; 2) synthesis of pyrroloisoquinolines from alkynylimino esters triggered by gold-catalyzed azomethine ylide formation; and 3) pyrrolizidine synthesis via three-component coupling reactions of iminoesters, acetylenes, and maleimides through the gold-catalyzed azomethine ylide generation/[3+2]-cycloaddition/enamine cyclization reaction.

Cyclobutenones and Benzocyclobutenones: Versatile Synthons in Organic Synthesis

Cyclobutenones, four-membered ketones bearing an unsaturated carbon-carbon double bond, and their structural sibling benzocyclobutenones, possess unique reactivity. Owing to their inherent high ring strain, such structures readily undergo ring opening under a variety of conditions, including thermolysis, photolysis, and transition metal catalysis, to afford reactive intermediates that can be trapped with nucleophiles, dienophiles, and unsaturated bonds. Their electron-deficient enone moieties are good electrophiles for facile nucleophilic addition. Such properties render cyclobutenones versatile synthons, serving as excellent coupling partners in a vast array of synthetically valuable transformations.