Sulfur in Waste-Free Sustainable Synthesis: Advancing Carbon-Carbon Coupling Techniques

This review explores the pivotal role of sulfur in advancing sustainable carbon-carbon (C-C) coupling reactions. The unique electronic properties of sulfur, as a soft Lewis base with significant mesomeric effect make it an excellent candidate for initiating radical transformations, directing C-H-activation, and facilitating cycloaddition and C-S bond dissociation reactions. These attributes are crucial for developing waste-free methodologies in green chemistry. Our mini-review is focused on existing sulfur-directed C-C coupling techniques, emphasizing their sustainability and comparing state-of-the-art methods with traditional approaches. The review highlights the importance of this research in addressing current challenges in organic synthesis and catalysis. The innovative use of sulfur in photocatalytic, electrochemical and metal-catalyzed processes not only exemplifies significant advancements in the field but also opens new avenues for environmentally friendly chemical processes. By focusing on atom economy and waste minimization, the analysis provides broad appeal and potential for future developments in sustainable organic chemistry.

Recent Advances in Alkenyl sp2 C-H and C-F Bond Functionalizations: Scope, Mechanism, and Applications

Alkenes and their derivatives are featured widely in a variety of natural products, pharmaceuticals, and advanced materials. Significant efforts have been made toward the development of new and practical methods to access this important class of compounds by selectively activating the alkenyl C(sp²)-H bonds in recent years. In this comprehensive review, we describe the state-of-the-art strategies for the direct functionalization of alkenyl sp² C-H and C-F bonds until June 2022. Moreover, metal-free, photoredox, and electrochemical strategies are also covered. For clarity, this review has been divided into two parts; the first part focuses on currently available alkenyl sp² C-H functionalization methods using different alkene derivatives as the starting materials, and the second part describes the alkenyl sp² C-F bond functionalization using easily accessible gem-difluoroalkenes as the starting material. This review includes the scope, limitations, mechanistic studies, stereoselective control (using directing groups as well as metal-migration strategies), and their applications to complex molecule synthesis where appropriate. Overall, this comprehensive review aims to document the considerable advancements, current status, and emerging work by critically summarizing the contributions of researchers working in this fascinating area and is expected to stimulate novel, innovative, and broadly applicable strategies for alkenyl sp² C-H and C-F bond functionalizations in the coming years.

Organic synthesis with the most abundant transition metal–iron: from rust to multitasking catalysts

The promising aspects of iron in synthetic chemistry are being explored for three-four decades as a green and eco-friendly alternative to late transition metals. This present review unveils these rich iron-chemistry towards different transformations.

Crystal structure, Hirshfeld surfaces, topology, energy frameworks and dielectric studies of 1-(2-chlorophenyl)- 3,3-bis(methylthio)prop-2-en-1-one

The title compound 1-(2-chlorophenyl)-3,3-bis(methylthio)prop-2-en-1-one (1) have been synthesized, crystallized and characterized using FT-IR, 1H NMR, 13C NMR, LCMS and confirmed by single crystal X-ray diffraction method. In addition, the intermolecular interactions in the crystal structure are analyzed using Hirshfeld surfaces computational method. The (1) crystallizes in a monoclinic crystal system (space group P 21/ c) with cell parameters a = 17.0132(9) Å, b = 8.6521(4) Å, c = 8.2815(7) Å, β = 95.512(6) ° and Z = 4. Intermolecular hydrogen bonds/interactions of the type C · · · H · · · O, C–H · · · S, C–H · · · Cg and C–Cl · · · Cg stabilize the crystal structure. The intermolecular interactions responsible for crystal packing are analyzed using Hirshfeld surfaces computational method, 2D finger print plots, electrostatic potential surfaces, toplogy surfaces [curvedness (C) and shape index (S), enrichment ratio (E) and 3D energy frameworks]. In addition the dielectric studies were performed for the title molecule. The crystal structure database (CSD) analysis was carried out for structural conformation and crystal packing confirmation. Overall structural studies confirmed that the intermolecular interactions of the type S · · · S chalocogen bonds are involved in crystal packing in addition to the C11–H11 · · · O1, C10–H10B · · · O1, two C10–H10 · · · S1, C4–H11 · · · Cg1 and C1–Cl1 · · · Cg1 interactions.

Palladium-Catalyzed C-S Bond Cleavage with Allenoates: Synthesis of Tetrasubstituted 2-Alkenylfuran Derivatives

Palladium-catalyzed C-S cleavage of tetrasubstituted internal alkene α-oxo ketene dithioacetals was realized with allenoates as the coupling partners, efficiently affording tetrasubstituted 2-alkenylfuran derivatives with excellent regioselectivity under mild conditions. Allenoates acted as C1 synthons in the desulfurative [4 + 1] annulation.

The theoretical chemical calculations clarify the mechanism of beta-alkylation of 1-phenylethanol with benzyl alcohol catalyzed by iron(ii) acetylacetonate methods

Iron(ii) acetylacetonate was suggested to be a better catalyst of the β-alkylation of 1-phenylethanol with benzyl alcohol to form 1,3-diphenyl-1-propanol. DFT calculations have been performed to study the internal mechanism, the structures of intermediates and transition states, and the exchange of electronic density in detail. The energetic results show that this β-alkylation reaction proceeds via the hydrogen autotransfer mechanism and the catalytic cycle includes three sequential stages: (1) alcohol oxidation to produce aldehyde associated with hydride anion transfer, (2) cross-aldol condensation to form a chalcone and (3) chalcone reduction with multi-step hydrogenation. In order to study whether the only by-product, water, has clearly influenced the reaction, eight catalyst hydrogenation pathways and four catalyst dehydrogenation pathways have been studied. We are delighted to find that the presence of the only by-product, water, can significantly increase the reduction energy barrier of dihydrochalcone. The energy barrier of the catalyst's hydrogenation is less than 6 kcal mol⁻¹. Our calculation results are fundamentally coincident with the experimental detections, and suggest that the crossing-coupling reaction occurs through a reliable mechanism. Two dihydrochalcone catalysts were designed on the basis of how the β-alkylation reaction proceeds.

Iron(ii) acetylacetonate was suggested to be a better catalyst of the β-alkylation of 1-phenylethanol with benzyl alcohol to form 1,3-diphenyl-1-propanol.

Copper-promoted direct C–H alkoxylation of S,S-functionalized internal olefins with alcohols

Efficient copper-promoted direct C–H alkoxylation of internal olefins, α-oxo ketene dithioacetals, was achieved with alcohols as the alkoxylating reagents.

Efficient trifluoromethylation of C(sp2)–H functionalized α-oxoketene dithioacetals: a route to the regioselective synthesis of functionalized trifluoromethylated pyrazoles

An operationally simple approach for regioselective construction of substituted trifluoromethylated pyrazoles via ligand free nucleophilic trifluoromethylation of iodo-substituted α-oxoketene dithioacetals.

Direct thiocyanation of ketene dithioacetals under transition-metal-free conditions

The first direct thiocyanation of ketene dithioacetals has been accomplished in the presence of N-chlorosuccinimide (NCS) and NH₄SCN under transition-metal-free conditions. Terminal alkenes and hydrazine were identified to be qualified candidates for the process as well.

A new approach for fused isoindolines via hexadehydro-Diels–Alder reaction (HDDA) by Fe(0) catalysis

A simple method has been developed for the synthesis of fused isoindolines via a cascade HDDA approach catalyzed by Fe₂(CO)₉.