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1. Progress on the Cu-Catalyzed 1,4-Conjugate Addition to Thiochromones

   https://doi.org/10.3390/catal13040713  

   Guo, Fenghai; Young, Jayla A.; Perez, Mina S.; Hankerson, Holden A.; Chavez, Alex M. (April 2023, Catalysts)

   Carbon–carbon bond formation is one of the most important tools in synthetic organic chemists’ toolbox. It is a fundamental transformation that allows synthetic chemists to synthesize the carbon framework of complex molecules from inexpensive simple starting materials. Among the many synthetic methodologies developed for the construction of carbon–carbon bonds, organocopper reagents are one of the most reliable organometallic reagents for this purpose. The versatility of organocuprate reagents or the reactions catalyzed by organocopper reagents were demonstrated by their applications in a variety of synthetic transformations including the 1,4-conjugate addition reactions. Sulfur-containing heterocyclic compounds are a much less studied area compared to oxygen-containing heterocycles but have gained more and more attention in recent years due to their rich biological activities and widespread applications in pharmaceuticals, agrochemicals, and material science. This paper will provide a brief review on recent progress on the synthesis of an important class of sulfur-heterocycles-2-alkylthiochroman-4-ones and thioflavanones via the conjugate additions of Grignard reagents to thiochromones catalyzed by copper catalysts. Recent progress on the synthesis of 2-substituted thiochroman-4-ones via alkynylation and alkenylation of thiochromones will also be covered in this review. 

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2. Phosphorus‐Directed C−H Borylation

   https://doi.org/10.1002/adsc.202100173  

   Auth, Marin_R; McGarry, Kathryn_A; Clark, Timothy_B (March 2021, Advanced Synthesis & Catalysis)

   Abstract Phosphorus‐containing compounds have a long history of utility in a broad range of fields, including agricultural, pharmaceutical, and metal‐mediated reactions. In recent decades, numerous methods have been developed to streamline the synthesis of organophosphorus reagents based on these numerous applications. This review focuses upon the recent development of phosphorus(III)‐ and phosphorus(V)‐directed C−H borylation reactions. This transformation has evolved significantly in the past two years, resulting in several new methods that provide access to organic substrates containing both phosphorus and boron. Further functionalization of the carbon−boron bond to provide functionalized organophosphorus products is discussed. magnified image 

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3. Recent advances in the synthesis and reactivity of azetidines: strain-driven character of the four-membered heterocycle

   https://doi.org/10.1039/d1ob00061f  

   Mughal, Haseeb; Szostak, Michal (April 2021, Organic & Biomolecular Chemistry)

   null (Ed.)

   Azetidines represent one of the most important four-membered heterocycles used in organic synthesis and medicinal chemistry. The reactivity of azetidines is driven by a considerable ring strain, while at the same the ring is significantly more stable than that of related aziridines, which translates into both facile handling and unique reactivity that can be triggered under appropriate reaction conditions. Recently, remarkable advances in the chemistry and reactivity of azetidines have been reported. In this review, we provide an overview of the synthesis, reactivity and application of azetidines that have been published in the last years with a focus on the most recent advances, trends and future directions. The review is organized by the methods of synthesis of azetidines and the reaction type used for functionalization of azetidines. Finally, recent examples of using azetidines as motifs in drug discovery, polymerization and chiral templates are discussed. 

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4. Recent strategies used in the synthesis of saturated four-membered heterocycles

   https://doi.org/10.1039/D1OB00988E  

   Malarney, Kien P.; KC, Shekhar; Schmidt, Valerie A. (October 2021, Organic & Biomolecular Chemistry)

   The importance and prevalance of O-, N-, and S-atom containing saturated four-membered ring motifs in biologically active molecules and potential therapeutics continues to drive efforts in their efficient synthetic preparation. In this review, general and recent strategies for the synthesis of these heterocycles are presented. Due to the limited potential bond disconnections, retrosynthetic strategies are broadly limited to cyclizations and cycloadditions. Nonetheless, diverse approaches for accessing cyclization precursors have been developed, ranging from nucleophilic substitution to C–H functionalization. Innovative methods for substrate activation have been developed for cycloadditions under photochemical and thermal conditions. Advances in accessing oxetanes, azetidines, and thietanes remain active areas of research with continued breakthroughs anticipated to enable future applications. 

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5. Photochemically and Thermally Generated BN-Doped Borafluorenate Heterocycles via Intramolecular Staudinger-Type Reactions

   https://doi.org/10.1021/acs.inorgchem.3c02284  

   Tra, Bi Youan; Molino, Andrew; Hollister, Kimberly K.; Sarkar, Samir Kumar; Dickie, Diane A.; Wilson, David J.; Gilliard, Robert J. (January 2023, Inorganic Chemistry)

   A series of BN-incorporated borafluorenate heterocycles, bis(borafluorene-phosphinimine)s (11–15), have been formed via intramolecular Staudinger-type reactions. The reactions were promoted by light or heat using monodentate phosphine-stabilized 9-azido-9-borafluorenes (R3P-BF-N3; 6–10) and involve the release of dinitrogen (N2), migration of phosphine from boron to nitrogen, and oxidation of the phosphorus center (PIII to PV). Density functional theory (DFT) calculations provide mechanistic insight into the formation of these compounds. Compounds 11–15 are blue emissive in the solution and solid states with absolute quantum yields (ΦF) ranging from 12 to 68%. 

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