Alternative Palladium-Catalyzed Vinylic C−H Difluoroalkylation of Ketene Dithioacetals Using Bromodifluoroacetate Derivatives

Visible-light-induced reactions of methylenecyclopropanes (MCPs)

Diverse, visible-light-induced transformations of methylenecyclopropanes (MCPs) have been reported in recent years, attracting significant attention from synthetic chemists. As readily accessible strained molecules, MCPs have sufficient reactivity to selectively generate different target products, through reactions with various radical species upon visible-light irradiation under regulated reaction conditions. These transformations can be classified into three subcategories of reaction pathway, forming ring-opened products, cyclopropane derivatives, and alkynes. These products include pharmaceutical intermediates and polycyclic/heterocyclic compounds that are challenging to obtain using traditional methods. This review summarizes the recent advancements in this field.

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.

Selectfluor-Promoted Intramolecular N-S Bond Formation of α-Carbamoyl Ketene Dithioacetals in the Presence of Water: Synthesis of Multifunctionalized Isothiazolones

A practical and efficient protocol toward fully substituted isothiazolones through Selectfluor-mediated intramolecular oxidative annulation of α-carbamoyl ketene dithioacetals has been developed in the presence of H₂O and metal-free conditions. Notably, the experimental results reveal that H₂O was crucial to the formation of new N-S bonds and the elimination of alkyl group from the sulfur atom. This protocol provides readily prepared substrates and possesses good functional group tolerance, mild reaction conditions, and operational simplicity, which provides potential access to applications in the pharmaceutical chemistry.

Transition metal free, green and facile halogenation of ketene dithioacetals using a KX–oxidant system

A facile oxidative halogenation of α-oxo ketene dithioacetals is achieved by using a potassium halide and an oxidant combination under transition metal free conditions at ambient temperature.

Synthetic methods for compounds containing fluoro-lactam units

In recent years, considerable attention has been devoted to the exploration of novel synthetic methods for fluoro-lactams due to their significant biological and pharmaceutical activities. This review summarizes recently established strategies for synthesizing fluorine-substituted lactams, including fluoro-β-lactams, fluoro-γ-lactams, and fluoro-δ-lactams. Additionally, the reaction scopes, limitations, and mechanisms are discussed.

Copper-Catalyzed Bromodifluoroacetylative Cyclization of Enynes

A copper-catalyzed bromodifluoroacetylative cyclization reaction is described. The treatment of bromodifluoroacete derivatives by CuI and B₂Pin₂ enables difluoroalkyl radical generation and triggers the radical addition/cyclization/bromination sequences. Bromodifluoroacetyl-derived ester, amide, and ketone were compatible and gave various vinyl C-Br bonds containing functionalized heterocycles in good yields.

Promising reagents for difluoroalkylation

This review describes recent advances in difluoroalkylation reactions using different substrates.

Metal free, facile sulfenylation of ketene dithioacetals catalyzed by an HBr–DMSO system

A transition metal free, efficient, sulfenylation of ketene dithioacetals catalyzed by an HBr–DMSO system is achieved. This strategy employs inexpensive and readily available HBr and DMSO to provide a direct C–H bond sulfenylation with a broad range of aryl thiols. This sulfenylated product is also transformed for the synthesis of pyrazole derivatives in excellent yield.

Copper-mediated cascade radical cyclization of olefins with naphthalenyl iododifluoromethyl ketones

Copper-mediated radical cyclization of naphthalenyl iododifluoromethyl ketones with olefins was developed to generate a series of unprecedented gem-difluorodihydrophenanthrenones with excellent regioselectivity.

Oxidant-controlled divergent transformations of 3-aminoindazoles for the synthesis of pyrimido[1,2-b]-indazoles and aromatic nitrile-derived dithioacetals

An oxidant-controlled divergent reactivity of 3-aminoindazoles is presented, which enables the [3 + 3] annulation and C–H arylation of ketene dithioacetals in disparate pathways to assemble pyrimido[1,2-b]-indazoles and aromatic nitrile-derived dithioacetals.

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.

Metal-Free Vinyl C-H Sulfenylation/Alkyl Thiolation of Ketene Dithioacetals for the Synthesis of Polythiolated Alkenes

The sulfenylation of the vinyl C-H bond in ketene dithioacetals leading to the synthesis of polythiolated alkenes is achieved via the promotion of molecular iodine. In addition, alkyl thiols also exhibit tolerance to the C-H bond elaboration reaction for the synthesis of corresponding alkylthiolated ketene dithioacetals.