Copper(I)-Catalyzed Intramolecular Trifluoromethylation of Methylenecyclopropanes

Substituent-Controlled Copper-Catalyzed Trifluoromethylation of 1,7-Dienes: Synthesis of Mono- and Bis-trifluoromethylated Benzoxepines

A copper-catalyzed trifluoromethylation of benzene-linked 1,7-dienes with 1-trifluoromethyl-1,2-benziodoxole via a radical cascade cyclization process for the synthesis of mono- and bis-trifluoromethylated benzoxepines is developed. The selectivity depends on substituents on the double bond of the allyl group in 1,7-dienes. The large-scale operation and late-stage functionalization of bioactive molecules reveal the promising utility of this protocol.

Divergent Fluorinations of Vinylcyclopropanes: Ring-Opening 1,5-Hydrofluorination and Ring-Retaining 1,2-Difluorination

Organofluorine compounds have been widely used in pharmaceutical, agrochemical, and material sciences. Reported herein are divergent fluorination reactions of vinylcyclopropanes with different electrophiles, which allow the facile synthesis of homoallylic monofluorides and vicinal-difluorides through ring-opening 1,5-hydrofluorination and ring-retaining 1,2-difluorination, respectively. Both protocols feature mild conditions, simple operations, good functional group tolerance, and generally good yields. The practicality of these reactions is demonstrated by their scalability, as well as the successful conversion of the formed homoallylic monofluorides into other complex fluorinated molecules.

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.

Oxidative functionalization of alkylidenecyclopropanes and alkylidenecyclobutanes: a versatile platform to access nitrated cyclopropanes and cyclobutanes

A divergent radical nitration of alkylidenecyclopropanes (ACPs) and alkylidenecyclobutanes (ACBs) with Fe(NO₃)₃·9H₂O or AgNO₂ has been achieved, affording three categories of products including β-nitro alcohol, α-nitro ketone and nitro nitratosation products with yields up to 90%. Particularly, the cyclopropyl and cyclobutyl rings were conserved in the products. The applicability of this method was demonstrated by the scale-up experiment and reduction of the nitro into an amino group. Preliminary mechanistic studies suggested that the nitro radical was involved in the reaction process.

Ru(II)- or Rh(III)-Catalyzed Annulation of Aromatic/Vinylic Acids with Alkylidenecyclopropanes via C-H Activation

An efficient and new route for the synthesis of (E)-4-benzylideneisochroman-1-ones through tandem cascade annulation of benzoic acids with alkylidenecyclopropanes using Ru(II) as a catalyst is demonstrated. It is important to note that the reaction delivers selectively E-stereoselective 4-benzylideneisochroman-1-one derivatives in moderate to good yields, which has completely diverse selectivity as compared with previous methods. Further, the annulation was explored with less-reactive β C-H activation of vinylic acids with alkylidenecyclopropanes, leading to the highly useful α-pyrone derivatives in the presence of an Rh(III) catalyst.

Recent Advances in Transition-Metal Mediated Trifluoromethylation Reactions

Fluorine compounds are known for their abundance in more than 20% of pharmaceutical and agrochemical products mainly due to the enhanced lipophilicity, metabolic stability and pharmacokinetic properties of organofluorides. Consequently,...

Construction of an isoquinolinone framework from carboxylic-ester-directed umpolung ring opening of methylenecyclopropanes

An interesting type of reaction involving functionalized methylenecyclopropanes (MCPs) has been revealed. Here, a nucleophilic attack of an anionic species onto a partially polarity-reversed MCP was realized by treating a neighbouring carboxylic ester tethered to the MCP and amine with KHMDS to realize an umpolung ring opening of the MCP. This work established an operationally convenient protocol for the rapid construction of isoquinolinone frameworks.

SbCl3 initiated conjunctive C-H bond functionalization and carbochlorination between glycine esters and methylenecyclopropanes (MCPs)

In the presence of dioxygen, an antimony trichloride enabled conjunctive sp³ C-H bond functionalization and carbochlorination of glycines was realized, providing a series of chlorinated quinolines in high yields. The mechanistic study shows that the antimony(V) species might be involved in the oxidation of the sp³ C-H bond and is followed by carbochlorination through a radical intermediate.

Thermally-Induced Intramolecular [4+2] Cycloaddition of Allylamino- or Allyloxy-Tethered Alkylidenecyclopropanes

A thermally-induced intramolecular [4+2] cycloaddition reaction of allylamino- or allyloxy-tethered alkylidenecyclopropanes has been reported in this paper, giving a new protocol for the rapid construction of polycyclic skeleton molecules in moderate to excellent yields with a broad substrate scope. On the basis of control experiments and DFT calculations, we disclosed that the reaction proceeded through a [4+2] cycloaddition and trace of water assisted 1,3-H shift process to give the target product.

A visible-light mediated ring opening reaction of alkylidenecyclopropanes for the generation of homopropargyl radicals

Classical cyclopropylcarbinyl radical clock reactions have been widely applied to conduct mechanistic studies for probing radical processes for a long time; however, alkylidenecyclopropanes, which have a similar molecular structure to methylcyclopropanes, surprisingly have not yet attracted researcher's attention for similar ring opening radical clock processes. In recent years, photocatalytic NHPI ester activation chemistry has witnessed significant blooming developments and provided new synthetic routes for cross-coupling reactions. Herein, we wish to report a non-classical ring opening radical clock reaction using innovative NHPI esters bearing alkylidenecyclopropanes upon photoredox catalysis, providing a brand-new synthetic approach for the direct preparation of a variety of alkynyl derivatives. The potential synthetic utility of this protocol is demonstrated in the diverse transformations and facile synthesis of bioactive molecules or their derivatives and medicinal substances.

Visible light mediated synthesis of 4-aryl-1,2-dihydronaphthalene derivatives via single-electron oxidation or MHAT from methylenecyclopropanes

A new synthetic strategy of a single-electron oxidation and MHAT of methylenecyclopropanes (MCPs) for the rapid construction of 4-aryl-1,2-dihydronaphthalene derivatives by merging photoredox catalysis and cobalt catalysis has been developed.

Recent Advances on Synthetic Methodology Merging C-H Functionalization and C-C Cleavage

The functionalization of C-H bonds has become a major thread of research in organic synthesis that can be assessed from different angles, for instance depending on the type of catalyst employed or the overall transformation that is carried out. This review compiles recent progress in synthetic methodology that merges the functionalization of C-H bonds along with the cleavage of C-C bonds, either in intra- or intermolecular fashion. The manuscript is organized in two main sections according to the type of substrate in which the cleavage of the C-C bond takes place, basically attending to the scission of strained or unstrained C-C bonds. Furthermore, the related research works have been grouped on the basis of the mechanistic aspects of the different transformations that are carried out, i.e.,: (a) classic transition metal catalysis where organometallic intermediates are involved; (b) processes occurring via radical intermediates generated through the use of radical initiators or photochemically; and (c) reactions that are catalyzed or mediated by suitable Lewis or Brønsted acid or bases, where molecular rearrangements take place. Thus, throughout the review a wide range of synthetic approaches show that the combination of C-H and C-C cleavage in single synthetic operations can serve as a platform to achieve complex molecular skeletons in a straightforward manner, among them interesting carbo- and heterocyclic scaffolds.

Copper-promoted cyanoalkylation/ring-expansion of vinylcyclopropanes with α-C-H bonds in alkylnitriles toward 3,4-dihydronaphthalenes

A copper-promoted oxidative cyanomethylation/ring-expansion of vinylcyclopropanes with α-C(sp3)-H bonds in alkyl nitriles is established for the generation of 1-cyanoethylated 3,4-dihydronaphthalenes. This cyanomethylation/ring-expansion involves a radical pathway and proceeds via cyanomethyl radical formation, radical addition and ring-expansion. This ring-expansion strategy offers a highly atom-economical route for the construction of nitrile-containing 3,4-dihydronaphthalenes, which can be transformed into other useful products under simple conditions.

Silver-promoted oxidative sulfonylation and ring-expansion of vinylcyclopropanes with sodium sulfinates leading to dihydronaphthalene derivatives

Silver-promoted sulfonylation and ring-expansion of vinylcyclopropanes with sodium sulfinates is established for the construction of 1-sulfonylmethylated 3,4-dihydronaphthalenes. This sulfonylation process involves a radical pathway, including sulfonyl radical formation, radical addition, ring-opening and cyclization. The 1-sulfonylmethylated 3,4-dihydronaphthalenes can be converted into other useful products.

Rapid construction of cyclopenta[b]naphthalene frameworks from propargylic alcohol tethered methylenecyclopropanes

We have developed a new synthetic methodology for the rapid construction of cyclopenta[b]naphthalene frameworks from the reaction of propargylic alcohol tethered methylenecyclopropanes with mesyl chloride in the presence of triethylamine through cascade cyclization. The reaction can be performed under mild conditions without the use of transition metals, affording the target products in moderate to good yields, and this cyclization reaction process can be scaled up to a gram-scale synthesis.

A highly efficient method for the construction of cyclopropane-containing dihydroindole derivatives from indolemethylenecyclopropanes with DIAD and DEAD

A highly efficient method for the construction of cyclopropane-containing dihydroindole derivatives from indolemethylenecyclopropanes with DIAD and DEAD has been disclosed. The transformation could occur under catalyst-free conditions at ambient temperature to afford dihyroindole derivatives in good yields. It has been proved that the strained moiety of methylenecyclopropane in the substrate of indolemethylenecyclopropane is critical and DFT calculations reveal that the reaction proceeds through a two-step pathway.

Visible-light photoredox-catalyzed dual C–C bond cleavage: synthesis of 2-cyanoalkylsulfonylated 3,4-dihydronaphthalenes through the insertion of sulfur dioxide

A novel visible-light photoredox-catalyzed dual C–C bond cleavage of methylenecyclopropanes and cycloketone oximes for accessing 2-cyanoalkylsulfonated 3,4-dihydronaphthalenes is established.

Lewis or Brønsted acid-catalysed reaction of propargylic alcohol-tethered alkylidenecyclopropanes with indoles and pyrroles for the preparation of polycyclic compounds tethered with indole or pyrrole motif

We developed a facile synthetic method to access the cyclopenta[b]naphthalene skeleton from Lewis or Brønsted acid-catalysed propargylic alcohol-tethered alkylidenecyclopropanes with indole and pyrrole derivatives.

Copper/B2pin2-Catalyzed Difluoroalkylation of Methylenecyclopropanes with Bromodifluorinated Acetates and Acetamides: One-Pot Synthesis of CF2-Containing Dihydronaphthalene Derivatives

Novel copper/B₂pin₂-catalyzed difluoroalkylation of methylenecyclopropanes with bromodifluorinated acetates and acetamides via a tandem radical process involving ring-opening/intramolecular cyclization has been reported. This protocol is not only tolerated to a diverse range of substrates but also applicable to the synthesis of useful difluoromethylated compounds. Moreover, the reaction could be performed on a gram scale with a high yield, which opens up the possibility for practical applications.

Oxidative radical ring-opening/cyclization of cyclopropane derivatives

The ring-opening/cyclization of cyclopropane derivatives has drawn great attention in the past several decades. In this review, recent efforts in the development of oxidative radical ring-opening/cyclization of cyclopropane derivatives, including methylenecyclopropanes, cyclopropyl olefins and cyclopropanols, are described. We hope this review will be of sufficient interest for the scientific community to further advance the application of oxidative radical strategies in the ring-opening/cyclization of cyclopropane derivatives.

Rh(i)-Catalyzed stereoselective intramolecular cycloaddition reactions of ene-vinylidenecyclopropanes for the construction of fused 6,5-bicyclic skeletons with a quaternary all-carbon stereocenter

Rh(i)-catalyzed asymmetric [3 + 2] cycloadditions of ene-VDCPs are demonstrated, producing cyclic ring structures with an all-carbon quaternary stereocenter in good yields with excellent enantioselectivities.

Silver-mediated oxidative C–C bond sulfonylation/arylation of methylenecyclopropanes with sodium sulfinates: facile access to 3-sulfonyl-1,2-dihydronaphthalenes

The novel AgNO₃-mediated sulfonylation/arylation of a C–C σ-bond in MCPs with sodium sulfinates to synthesize 3-sulfonylated 1,2-dihydronaphthalenes is reported.

Rh(i)-Catalyzed intramolecular [3 + 2] cycloaddition reactions of yne-vinylidenecyclopropanes

A Rh(i)-catalyzed intramolecular [3 + 2] cycloaddition reaction of yne-vinylidenecyclopropanes has been developed, providing fused [6.5]-bicyclic products in moderate to good yields.

Recent Advances in the Cycloisomerizations of Methylenecyclopropanes using Gold Catalysis

During the past decades, cycloisomerizations of methylenecyclopropanes using gold catalysis have attracted much attention from organic chemists. The different patterns of gold(I)-catalyzed cycloisomerizations of methylenecyclopropanes have been developed, and they can be classified as ring-opening and ring-expansion reaction patterns. This synthetic methodology provides a new approach to novel cyclic- or polycyclic compounds. The corresponding products have great potential for material science, medicinal chemistry and total synthesis. This Concept article will mainly focus on the recent advances in the cycloisomerizations of methylenecyclopropanes in the past four years.

Oxidative C-C Bond Functionalization of Methylenecyclopropanes with Aldehydes for the Formation of 2-Acyl-3,4-dihydronaphthalenes

A new FeCl₂- and DTBP (di- tert-butyl peroxide)-promoted oxidative ring-opening and cyclization of methylenecyclopropanes with aldehydes for the synthesis of 2-acyl-3,4-dihydronaphthalenes is presented. This oxidative cyclization reaction proceeds via a radical addition, ring-opening, and cyclization sequence facilitated by a Lewis acid, and it offers a practical and straightforward route for the oxidative cyclization of methylenecyclopropanes with an aromatic carbon and a C(sp²)-H bond by simultaneously forming two new carbon-carbon bonds.

Gold- and silver-catalyzed intramolecular annulation and rearrangement of aniline-linked 1,6-enynes containing methylenecyclopropanes

A new synthetic approach for the construction of 1,2-dihydroquinolines having a methylenecyclopropane moiety or a cyclobutene moiety has been developed from gold- and silver-catalyzed annulation of N-tethered 1,6-enynes containing methylenecyclopropanes.

Palladium-catalyzed intramolecular transfer hydrogenation & cycloaddition of p-quinamine-tethered alkylidenecyclopropanes to synthesize perhydroindole scaffolds

A facile Pd-catalyzed intramolecular transfer hydrogenation and cycloaddition of p-quinamine-tethered alkylidenecyclopropanes has been developed, giving rigid tricyclic perhydroindole skeletons in moderate to good yields.

Gold-catalyzed ring enlargement and cycloisomerization of alkynylamide tethered alkylidenecyclopropanes

A gold(i)-catalyzed ring enlargement and cycloisomerization of alkynylamide tethered alkylidenecyclopropanes has been developed, providing facile access to functionalized polycyclic and spiropolycyclic products based on the use of gold(i) catalysts.

Synthesis of 3-(((2,3-dihydrobenzofuran-3-yl)methyl)sulfonyl) coumarins through the reaction of 2-(allyloxy)anilines, sulfur dioxide, and aryl propiolates

A facile route to 3-(((2,3-dihydrobenzofuran-3-yl)methyl)sulfonyl) coumarins through the reaction of 2-(allyloxy)anilines, sulfur dioxide, and aryl propiolates is achieved.

Iron-catalyzed or iodine-induced intramolecular halocyclization of N-vinyl-tethered methylenecyclopropanes: facile access to halogenated 1,2-dihydroquinolines

Iron(iii) catalyst or I₂ acts as a Lewis acid to activate enamines, affording the corresponding halogenated 1,2-dihydroquinolines in good yields.

A gold(i)-catalyzed intramolecular tandem cyclization reaction of alkylidenecyclopropane-containing alkynes

A novel strategy for the gold(i)-catalyzed intramolecular tandem cyclization reaction of ortho-(arylethynyl)arenemethylenecyclopropanes has been developed, providing a facile access to functionalized 11H-benzo[a]fluorene derivatives.

Copper-catalyzed trifluoromethylazidation and rearrangement of aniline-linked 1,7-enynes: access to CF3-substituted azaspirocyclic dihydroquinolin-2-ones and furoindolines

A set of reactions involving copper-catalyzed trifluoromethylazidation and then rearrangement of aniline-linked 1,7-enynes was developed, and provided facile access to azaspirocyclic dihydroquinolin-2-ones, furoindolines and functionalized aziridines.

Recent advances in the chemical transformations of functionalized alkylidenecyclopropanes (FACPs)

Classification of functionalized alkylidenecyclopropanes (FACPs) and recent chemical transformations for the synthesis of novel and useful polycyclic and heterocyclic compounds.