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Compared to the outstanding development in the synthesis of Si−B single bonded species, borylsilanes and their application to organic synthesis, the chemistry of Si=B double bonded species, borasilenes and boratasilenes have only made little progress, first of all, due to the difficulties in accessing such double bonds. Herein we report the synthesis of the first Si=B analogue of a vinyl halide, a bromoboratasilene, via formal borylene insertion to the coordination sphere of a monoatomic Si(0) complex, using a dihaloborane as the borylene source. The treatment of bromoboratasilene toward neutral or anionic Lewis bases gives access to new boratasilenes, all of which were proved to possess significant Si=B double bond character by XRD analysis and DFT calculations. These results demonstrate exciting strategies to synthesize new types of Si=B double bonded species which should further progress the chemistry of boron, silicon‐containing molecules. [ABSTRACT FROM AUTHOR]

Compared to the outstanding development in the synthesis of Si−B single bonded species, borylsilanes and their application to organic synthesis, the chemistry of Si=B double bonded species, borasilenes and boratasilenes have only made little progress, first of all, due to the difficulties in accessing such double bonds. Herein we report the synthesis of the first Si=B analogue of a vinyl halide, a bromoboratasilene, via formal borylene insertion to the coordination sphere of a monoatomic Si(0) complex, using a dihaloborane as the borylene source. The treatment of bromoboratasilene toward neutral or anionic Lewis bases gives access to new boratasilenes, all of which were proved to possess significant Si=B double bond character by XRD analysis and DFT calculations. These results demonstrate exciting strategies to synthesize new types of Si=B double bonded species which should further progress the chemistry of boron, silicon‐containing molecules. [ABSTRACT FROM AUTHOR]

The Chemical Communications journal, published by The Royal Society of Chemistry, features articles on various topics such as advances in oxygen catalysis, total synthesis of natural products, and the synthesis of different chemical compounds. The journal also covers research on batteries, energy storage, and the development of new materials for various applications. The articles in this issue highlight recent advancements in the field of chemistry and showcase innovative research in the chemical sciences. [Extracted from the article]

A stereoselective hydroxyallylation reaction of cyclopropenes with cyclopropanols is achieved under zinc‐mediated conditions, affording densely functionalized cyclopropanes with excellent diastereocontrol over three contiguous stereocenters within and outside the cyclopropane ring. A racemic variant of the reaction is synergistically promoted by catalytic N‐heterocyclic carbene (NHC) and organic base, whereas chiral amino alcohol‐derived bifunctional NHC enables a catalytic enantioselective variant. The reaction likely involves the generation of enolized zinc homoenolate via ring‐opening of zinc cyclopropoxide and enolization of the resulting homoenolate, followed by its addition to the cyclopropene as a prochiral allylzinc nucleophile. Our mechanistic investigations highlighted the transient nature of enolized homoenolate, which, once generated from thermodynamically predominant cyclopropoxide, immediately proceeds to allylzincation with cyclopropene. The NHC not only promotes the rate‐determining generation of enolized homoenolate but also engages in the allylzincation process. The resulting cyclopropylzinc species undergoes partial in situ protonation while partially remaining intact, thereby leaving an opportunity for trapping with an external electrophile. [ABSTRACT FROM AUTHOR]

The synthesis of housane derivatives from cyclopropenes is described. Under rhodium(II) catalysis, cyclopropenylvinyl carbinols can regioselectively generate a carbene intermediate which undergoes an intramolecular cyclopropanation to form a housane, a skeleton with similar ring strain as the cyclopropene precursor. The procedure shows a remarkable broad scope and efficiency. Moreover, the method served to prepare man‐made housane‐containing terpene derivatives, which are not accessible by Nature. [ABSTRACT FROM AUTHOR]

A stereoselective hydroxyallylation reaction of cyclopropenes with cyclopropanols is achieved under zinc‐mediated conditions, affording densely functionalized cyclopropanes with excellent diastereocontrol over three contiguous stereocenters within and outside the cyclopropane ring. A racemic variant of the reaction is synergistically promoted by catalytic N‐heterocyclic carbene (NHC) and organic base, whereas chiral amino alcohol‐derived bifunctional NHC enables a catalytic enantioselective variant. The reaction likely involves the generation of enolized zinc homoenolate via ring‐opening of zinc cyclopropoxide and enolization of the resulting homoenolate, followed by its addition to the cyclopropene as a prochiral allylzinc nucleophile. Our mechanistic investigations highlighted the transient nature of enolized homoenolate, which, once generated from thermodynamically predominant cyclopropoxide, immediately proceeds to allylzincation with cyclopropene. The NHC not only promotes the rate‐determining generation of enolized homoenolate but also engages in the allylzincation process. The resulting cyclopropylzinc species undergoes partial in situ protonation while partially remaining intact, thereby leaving an opportunity for trapping with an external electrophile. [ABSTRACT FROM AUTHOR]

The synthesis of housane derivatives from cyclopropenes is described. Under rhodium(II) catalysis, cyclopropenylvinyl carbinols can regioselectively generate a carbene intermediate which undergoes an intramolecular cyclopropanation to form a housane, a skeleton with similar ring strain as the cyclopropene precursor. The procedure shows a remarkable broad scope and efficiency. Moreover, the method served to prepare man‐made housane‐containing terpene derivatives, which are not accessible by Nature. [ABSTRACT FROM AUTHOR]

In the context of the growing importance of heterocyclic compounds across various disciplines, numerous strategies for their construction have emerged. Exploiting the distinctive properties of cyclopropenes, this study introduces an innovative approach for the synthesis of benzo‐fused five‐membered oxa‐ and aza‐heterocycles through a formal [4+1] cyclization and subsequent acid‐catalyzed intramolecular O‐ to N‐ rearrangement. These transformations exhibit mild reaction conditions and a wide substrate scope. The applications in the late‐stage modification of complex molecules and in the synthesis of a potential PD‐L1 gene down‐regulator, make this method highly appealing in related fields. Combined experimental mechanistic studies and DFT calculations demonstrate Rh(III)‐mediated sequential C─H coupling/π‐allylation/dynamically favorable O‐attack route. [ABSTRACT FROM AUTHOR]

Herein we report a platinum‐catalyzed isomerization of cyclopropenes to 1,3‐dienes. Diverse dienylated alcohols were obtained in 42–98 % yield. The synthetic potential of the products was demonstrated by their use in Diels–Alder cycloadditions with various dienophiles. Isotope labelling studies provide strong support for a mechanism involving pericyclic [1,5]‐σ‐bond rearrangement of a vinyl platinum carbene intermediate. [ABSTRACT FROM AUTHOR]

Unstable tetra(methoxycarbonyl)cyclopentadienone was investigated in the synthesis of electron-deficient cycloheptatrienes via [4+2]-cycloaddition/cycloelimination reaction with cyclopropenes. The use of its stable dimer did not afford the product although similar reactions with alkynes have been reported. Quantum chemical calculation revealed that cyclopentadienone is not generated from the dimer and the reaction with alkynes proceeds via a more complicated cycloelimination/cycloaddition/cycloelimination cascade. However, the formation of cycloheptatrienes was found favorable over the formation of the dimer. Therefore, the trapping of tetra(methoxycarbonyl)cyclopentadienone upon formation was successful to give cycloheptatrienes with five ester groups. The use of methyl coumalate as a four-electron component was successful with cyclopropenes containing only one ester group to afford only two ester groups in the product. [ABSTRACT FROM AUTHOR]

A photocatalytic decarboxylative functionalization of cyclopropenes is reported. Starting from a broad range of redox‐active ester‐substituted cyclopropenes, cyclopropenylphthalimides can be synthesized in the absence of a nucleophile. Alternatively, different carbon and heteroatom nucleophiles can be introduced. The transformation proceeds most probably through the formation of an aromatic cyclopropenium cation, followed by trapping with the nucleophiles. [ABSTRACT FROM AUTHOR]

A photocatalytic decarboxylative functionalization of cyclopropenes is reported. Starting from a broad range of redox‐active ester‐substituted cyclopropenes, cyclopropenylphthalimides can be synthesized in the absence of a nucleophile. Alternatively, different carbon and heteroatom nucleophiles can be introduced. The transformation proceeds most probably through the formation of an aromatic cyclopropenium cation, followed by trapping with the nucleophiles. [ABSTRACT FROM AUTHOR]

The document is the contents list for an issue of the journal Chemical Communications. It includes highlights, cover images, and a list of articles and authors featured in the issue. The journal is published by The Royal Society of Chemistry and aims to connect the world with the chemical sciences. The articles cover a range of topics including asymmetric synthesis, solid-electrolyte interface layers, metal selenides, and various catalytic applications. [Extracted from the article]

A KOtBu-catalyzed ring-opening gem-silylborylation of cyclopropenes with silylboronates has been developed for the synthesis of (1-silyl)allylboronates, a useful class of compounds in organic synthesis. The reaction proceeds with high selectivity under mild conditions, and the reaction mechanism has been theoretically investigated using DFT calculations. [ABSTRACT FROM AUTHOR]

A three-component organocatalytic reaction of 1,3-dipolar cycloaddition between the in situ generated azomethine ylides and 3-substituted 1,2-diphenylcyclopropenes is described. The azomethine ylides have been generated via condensation of aromatic compounds (such as isatins and acenaphthenequinone) with benzylamines. The reaction has afforded derivatives of 3-azabicyclo[3.1.0]hexane, spiro-fused with the fragments of 2-oxindole and acenaphthylene-1(2H)-one. The cycloadducts have been obtained with yield up to 91%, mainly as individual diastereomers. The influence of bifunctional squaramide-based organocatalysts on the course of these three-component reactions has been investigated. Antiproliferative activity of selected synthesized compounds with respect to the human erythromyelosis (K562) and melanoma (Sk-mel-2) cell lines has been assessed in vitro by means of MTS analysis. [ABSTRACT FROM AUTHOR]

Addition polymerization of 3-methyl-3-phenylcyclopropene and 3,3-di(n-propyl)cyclopropene in the presence of a palladium complex containing an acyclic diaminocarbene ligand was studied. When activated with the organoborate (Na+[B(3,5-(CF3)2C6H3)4]–), such complex catalyzes the addition polymerization of substituted cyclopropenes. The polymerization occurs selectively without opening of the cyclopropane ring. The copolymerization of 3,3-di(n-propyl)cyclopropene with a monomer of the norbornene series (5-ethylidene-2-norbornene) was monitored by a decrease in the intensity of the characteristic signals in the 1H NMR spectra of the corresponding monomers. The substituted cyclopropenes were found to be more active monomers than norbornenes in the addition polymerization. The addition homopolymers of 3-methyl-3-phenylcyclopropene and 3,3-di(n-propyl)cyclopropene were characterized by differential scanning calorimetry, thermogravimetric analysis, and X-ray diffraction. [ABSTRACT FROM AUTHOR]

Heavy‐atom tunneling limits the lifetime and observability of bicyclo[4.1.0]hepta‐2,4,6‐triene, a key intermediate in the rearrangement of phenylcarbene. Bicyclo[4.1.0]hepta‐2,4,6‐triene had been proposed as the primary intermediate of the rearrangement of phenylcarbene, but despite many efforts evaded its characterization even in cryogenic matrices. By introducing fluorine substituents into the ortho‐positions of the phenyl ring of phenylcarbene, the highly strained cyclopropene 1,5‐difluorobicyclo[4.1.0]hepta‐2,4,6‐triene becomes stable enough to be characterized in argon matrices. However, even at 3 K this cyclopropene is only metastable and rearranges via heavy‐atom tunneling to the corresponding cycloheptatetraene. Calculations suggest that fluorination is necessary to slow down the tunneling rearrangement of the bicycloheptatriene. The parent bicycloheptatriene rapidly rearranges via heavy‐atom tunneling and therefore cannot be detected under matrix isolation conditions. [ABSTRACT FROM AUTHOR]

Heavy‐atom tunneling limits the lifetime and observability of bicyclo[4.1.0]hepta‐2,4,6‐triene, a key intermediate in the rearrangement of phenylcarbene. Bicyclo[4.1.0]hepta‐2,4,6‐triene had been proposed as the primary intermediate of the rearrangement of phenylcarbene, but despite many efforts evaded its characterization even in cryogenic matrices. By introducing fluorine substituents into the ortho‐positions of the phenyl ring of phenylcarbene, the highly strained cyclopropene 1,5‐difluorobicyclo[4.1.0]hepta‐2,4,6‐triene becomes stable enough to be characterized in argon matrices. However, even at 3 K this cyclopropene is only metastable and rearranges via heavy‐atom tunneling to the corresponding cycloheptatetraene. Calculations suggest that fluorination is necessary to slow down the tunneling rearrangement of the bicycloheptatriene. The parent bicycloheptatriene rapidly rearranges via heavy‐atom tunneling and therefore cannot be detected under matrix isolation conditions. [ABSTRACT FROM AUTHOR]

The selective activation of C–C bonds holds vast promise for catalysis. So far, research has been primarily directed at rhodium and nickel under harsh reaction conditions. Herein, we report C–C insertion reactions of a 12-electron palladium(0) surrogate stabilized by a cyclic(alkyl)(amino) carbene (CAAC) ligand. Benzonitrile (1), biphenylene (2), benzocyclobutenone (3), and naphtho[b]cyclopropene (4) were studied. These substrates allow elucidation of the effect of ring strain as well as hybridization encompassing sp3, sp2 and sp hybridized carbon atoms. All reactions proceed quantitatively at or below room temperature. This work therefore outlines perspectives for mild C–C bond functionalization catalysis. [ABSTRACT FROM AUTHOR]

Herein, a copper(I)‐catalyzed asymmetric hydrophosphination of 3,3‐disubstituted cyclopropenes is reported. It provides a series of phosphine derivatives in high to excellent diastereo‐ and enantioselectivities. The methodology enjoys broad substrate scope on both 3,3‐disubstituted cyclopropenes and diarylphosphines. The high stereoselectivity is attributed to both the high stability of the Cu(I)‐(R,R)‐QUINOXP* complex in the presence of stoichiometric HPPh2 and the produced phosphines, and the high‐performance asymmetric induction of the Cu(I)‐(R,R)‐QUINOXP* complex. Finally, the method is used for the synthesis of new chiral phosphine‐olefin compounds built on a cyclopropane skeleton, one of which serves as a wonderful ligand in Rh‐catalyzed asymmetric conjugate addition of phenylboronic acid to various α,β‐unsaturated compounds. [ABSTRACT FROM AUTHOR]

Herein, a copper(I)‐catalyzed asymmetric hydrophosphination of 3,3‐disubstituted cyclopropenes is reported. It provides a series of phosphine derivatives in high to excellent diastereo‐ and enantioselectivities. The methodology enjoys broad substrate scope on both 3,3‐disubstituted cyclopropenes and diarylphosphines. The high stereoselectivity is attributed to both the high stability of the Cu(I)‐(R,R)‐QUINOXP* complex in the presence of stoichiometric HPPh2 and the produced phosphines, and the high‐performance asymmetric induction of the Cu(I)‐(R,R)‐QUINOXP* complex. Finally, the method is used for the synthesis of new chiral phosphine‐olefin compounds built on a cyclopropane skeleton, one of which serves as a wonderful ligand in Rh‐catalyzed asymmetric conjugate addition of phenylboronic acid to various α,β‐unsaturated compounds. [ABSTRACT FROM AUTHOR]

We evaluate the accuracy of CCSD(T) and density functional theory (DFT) methods for the calculation of equilibrium rotational constants ( A e , B e , and C e ) for four experimentally detected low-lying C 5 H 2 isomers (ethynylcyclopropenylidene (2), pentatetraenylidene (3), ethynylpropadienylidene (5), and 2-cyclopropen-1-ylidenethenylidene (8)). The calculated rotational constants are compared to semi-experimental rotational constants obtained by converting the vibrationally averaged experimental rotational constants ( A 0 , B 0 , and C 0 ) to equilibrium values by subtracting the vibrational contributions (calculated at the B3LYP/jun-cc-pVTZ level of the theory). The considered isomers are closed-shell carbenes, with cumulene, acetylene, or strained cyclopropene moieties, and are therefore highly challenging from an electronic structure point of view. We consider both frozen-core and all-electron CCSD(T) calculations, as well as a range of DFT methods. We find that calculating the equilibrium rotational constants of these C 5 H 2 isomers is a difficult task, even at the CCSD(T) level. For example, at the all-electron CCSD(T)/cc-pwCVTZ level of the theory, we obtain percentage errors ≤0.4% ( C e of isomer 3, B e and C e of isomer 5, and B e of isomer 8) and 0.9–1.5% ( B e and C e of isomer 2, A e of isomer 5, and C e of isomer 8), whereas for the A e rotational constant of isomers 2 and 8 and B e rotational constant of isomer 3, high percentage errors above 3% are obtained. These results highlight the challenges associated with calculating accurate rotational constants for isomers with highly challenging electronic structures, which is further complicated by the need to convert vibrationally averaged experimental rotational constants to equilibrium values. We use our best CCSD(T) rotational constants (namely, ae-CCSD(T)/cc-pwCVTZ for isomers 2 and 5, and ae-CCSD(T)/cc-pCVQZ for isomers 3 and 8) to evaluate the performance of DFT methods across the rungs of Jacob's Ladder. We find that the considered pure functionals (BLYP-D3BJ, PBE-D3BJ, and TPSS-D3BJ) perform significantly better than the global and range-separated hybrid functionals. The double-hybrid DSD-PBEP86-D3BJ method shows the best overall performance, with percentage errors below 0.5% in nearly all cases. [ABSTRACT FROM AUTHOR]

Herein, we disclose the first regio‐, site‐ and chemoselective late‐stage (hetero)aryl C−H bond cyclopropenylation with cyclopropenium cations (CPCs). The process is fast, operationally simple and shows an excellent functional group tolerance in densely‐functionalized drug molecules, natural products, agrochemicals and fluorescent dyes. Moreover, we discovered that the installation of the cyclopropene ring in drug molecules could not only be used to shield against metabolic instability but also as a synthetic tool to reach medicinally‐relevant sp3‐rich scaffolds exploiting the highly‐strained nature of the cyclopropene ring with known transformations. [ABSTRACT FROM AUTHOR]

Herein, we disclose the first regio‐, site‐ and chemoselective late‐stage (hetero)aryl C−H bond cyclopropenylation with cyclopropenium cations (CPCs). The process is fast, operationally simple and shows an excellent functional group tolerance in densely‐functionalized drug molecules, natural products, agrochemicals and fluorescent dyes. Moreover, we discovered that the installation of the cyclopropene ring in drug molecules could not only be used to shield against metabolic instability but also as a synthetic tool to reach medicinally‐relevant sp3‐rich scaffolds exploiting the highly‐strained nature of the cyclopropene ring with known transformations. [ABSTRACT FROM AUTHOR]

The asymmetric hydrophosphination of cyclopropenes with phosphines is of much interest and importance, but has remained hardly explored to date probably because of the lack of suitable catalysts. We report here the diastereo‐ and enantioselective hydrophosphination of 3,3‐disubstituted cyclopropenes with phosphines by a chiral lanthanocene catalyst bearing the C2‐symmetric 5,6‐dioxy‐4,7‐trans‐dialkyl‐substituted tetrahydroindenyl ligands. This protocol offers a selective and efficient route for the synthesis of a new family of chiral phosphinocyclopropane derivatives, featuring 100 % atom efficiency, good diastereo‐ and enantioselectivity, broad substrate scope, and no need for a directing group. [ABSTRACT FROM AUTHOR]

The asymmetric hydrophosphination of cyclopropenes with phosphines is of much interest and importance, but has remained hardly explored to date probably because of the lack of suitable catalysts. We report here the diastereo‐ and enantioselective hydrophosphination of 3,3‐disubstituted cyclopropenes with phosphines by a chiral lanthanocene catalyst bearing the C2‐symmetric 5,6‐dioxy‐4,7‐trans‐dialkyl‐substituted tetrahydroindenyl ligands. This protocol offers a selective and efficient route for the synthesis of a new family of chiral phosphinocyclopropane derivatives, featuring 100 % atom efficiency, good diastereo‐ and enantioselectivity, broad substrate scope, and no need for a directing group. [ABSTRACT FROM AUTHOR]

Cyclopropene hydrofunctionalization has been a promising strategy for accessing multi‐substituted cyclopropanes; however, cyclopropene hydroalkylation remains underdeveloped. Herein, we report a low‐valent CoH‐catalyzed facial‐selective cyclopropene hydroalkylation to access multi‐substituted cyclopropanes. This reaction exhibits a broad substrate scope of alkyl halides and cyclopropenes and tolerates many functional groups. Moderate‐to‐good facial‐selectivity is obtained without any directing groups. Mechanism studies provide evidence that alkyl radicals are generated from alkyl halides and irreversible CoH insertion is responsible for the facial‐selectivity. Our preliminary exploration demonstrates that asymmetric cyclopropene hydroalkylation can be realized without conspicuous auxiliary groups. [ABSTRACT FROM AUTHOR]

Cyclopropene hydrofunctionalization has been a promising strategy for accessing multi‐substituted cyclopropanes; however, cyclopropene hydroalkylation remains underdeveloped. Herein, we report a low‐valent CoH‐catalyzed facial‐selective cyclopropene hydroalkylation to access multi‐substituted cyclopropanes. This reaction exhibits a broad substrate scope of alkyl halides and cyclopropenes and tolerates many functional groups. Moderate‐to‐good facial‐selectivity is obtained without any directing groups. Mechanism studies provide evidence that alkyl radicals are generated from alkyl halides and irreversible CoH insertion is responsible for the facial‐selectivity. Our preliminary exploration demonstrates that asymmetric cyclopropene hydroalkylation can be realized without conspicuous auxiliary groups. [ABSTRACT FROM AUTHOR]

Reactions of terminal alkynes (alkyl−C≡CH) and internal alkynes with rhenium(III) phosphine complex ReCl3(PMePh2)3 were studied, producing cationic mononuclear bi(rhenacyclopropene) complexes and η2‐alkyne complexes, respectively. The bi(rhenacyclopropene) complexes represent rare examples of well‐defined mononuclear metal complexes containing two η2‐vinyl ligands, as well as bis(dialkylcarbene) complexes of transition metals. [ABSTRACT FROM AUTHOR]

Ring structures such as pyridine, cyclopentane or their combinations are important motifs in bioactive molecules. In contrast to previous cycloaddition reactions that necessitated a directly bonded initiating functional group, this work demonstrated a novel through‐(hetero)arene radical transmission concept for selective activation of a remote bond. An efficient, metal‐free and atom‐economical [3+2] cycloaddition between 4‐pyridinyl cyclopropanes and alkenes or alkynes has been developed for modular synthesis of pyridine‐substituted cyclopentanes, cyclopentenes and bicyclo[2.1.1]hexanes that are difficult to access using known methods. This complexity‐building reaction was catalyzed by a very simple and inexpensive diboron(4) compound and took place via dearomative/rearomative processes. The substrate scope was broad and more than 100 new compounds were prepared in generally high yields. Mechanistic experiments and density function theory (DFT) investigation supported a radical relay catalytic cycle involving alkylidene dihydropyridine radical intermediates and boronyl radical transfer. [ABSTRACT FROM AUTHOR]

Ring structures such as pyridine, cyclopentane or their combinations are important motifs in bioactive molecules. In contrast to previous cycloaddition reactions that necessitated a directly bonded initiating functional group, this work demonstrated a novel through‐(hetero)arene radical transmission concept for selective activation of a remote bond. An efficient, metal‐free and atom‐economical [3+2] cycloaddition between 4‐pyridinyl cyclopropanes and alkenes or alkynes has been developed for modular synthesis of pyridine‐substituted cyclopentanes, cyclopentenes and bicyclo[2.1.1]hexanes that are difficult to access using known methods. This complexity‐building reaction was catalyzed by a very simple and inexpensive diboron(4) compound and took place via dearomative/rearomative processes. The substrate scope was broad and more than 100 new compounds were prepared in generally high yields. Mechanistic experiments and density function theory (DFT) investigation supported a radical relay catalytic cycle involving alkylidene dihydropyridine radical intermediates and boronyl radical transfer. [ABSTRACT FROM AUTHOR]

Enantiomerically enriched cyclopropyl ethers, amines, and cyclopropylazole derivatives possessing three stereogenic carbon atoms in a small cycle are obtained via the diastereoselective, formal nucleophilic substitution of chiral, non-racemic bromocyclopropanes. The key feature of this methodology is the utilization of the chiral center of the cyclopropene intermediate, which governs the configuration of the two adjacent stereocenters that are successively installed via 1,4-addition/epimerization sequence. [ABSTRACT FROM AUTHOR]

In the field of lipid research, bioorthogonal chemistry has made the study of lipid uptake and processing in living systems possible, whilst minimising biological properties arising from detectable pendant groups. To allow the study of unsaturated free fatty acids in live cells, we here report the use of sterculic acid, a 1,2‐cyclopropene‐containing oleic acid analogue, as a bioorthogonal probe. We show that this lipid can be readily taken up by dendritic cells without toxic side effects, and that it can subsequently be visualised using an inverse electron‐demand Diels–Alder reaction with quenched tetrazine‐fluorophore conjugates. In addition, the lipid can be used to identify changes in protein oleoylation after immune cell activation. Finally, this reaction can be integrated into a multiplexed bioorthogonal reaction workflow by combining it with two sequential copper‐catalysed Huisgen ligation reactions. This allows for the study of multiple biomolecules in the cell simultaneously by multimodal confocal imaging. [ABSTRACT FROM AUTHOR]

In the field of lipid research, bioorthogonal chemistry has made the study of lipid uptake and processing in living systems possible, whilst minimising biological properties arising from detectable pendant groups. To allow the study of unsaturated free fatty acids in live cells, we here report the use of sterculic acid, a 1,2‐cyclopropene‐containing oleic acid analogue, as a bioorthogonal probe. We show that this lipid can be readily taken up by dendritic cells without toxic side effects, and that it can subsequently be visualised using an inverse electron‐demand Diels–Alder reaction with quenched tetrazine‐fluorophore conjugates. In addition, the lipid can be used to identify changes in protein oleoylation after immune cell activation. Finally, this reaction can be integrated into a multiplexed bioorthogonal reaction workflow by combining it with two sequential copper‐catalysed Huisgen ligation reactions. This allows for the study of multiple biomolecules in the cell simultaneously by multimodal confocal imaging. [ABSTRACT FROM AUTHOR]

The formation of polysubstituted cyclopropane derivatives in the gold(I)-catalyzed reaction of olefins and propargylic esters is a potentially useful transformation to generate diversity, therefore any method in which its stereoselectivity could be controlled is of significant interest. We prepared and tested a series of chiral gold(I)-carbene complexes as a catalyst in this transformation. With a systematic optimization of the reaction conditions, we were able to achieve high enantioselectivity in the test reaction while the cis:trans selectivity of the transformation was independent of the catalyst. Using the optimized conditions, we reacted a series of various olefins and acetylene derivatives to find that, although the reactions proceeded smoothly and the products were usually isolated in good yield and with good to exclusive cis selectivity, the observed enantioselectivity varied greatly and was sometimes moderate at best. We were unable to establish any structure-property relationship, which suggests that for any given reagent combination, one has to identify individually the best catalyst. [ABSTRACT FROM AUTHOR]

Azepanes are important seven‐membered heterocycles, which are present in numerous natural and synthetic compounds. However, the development of convergent synthetic methods to access them remains challenging. Herein, we report the Lewis acid catalyzed (4+3) annulative addition of aryl and amino donor‐acceptor cyclopropanes with 2‐aza‐1,3‐dienes. Densely substituted azepane derivatives were obtained in good to excellent yields and with high diastereoselectivity. The reaction occurred under mild conditions with ytterbium triflate as the catalyst. The use of copper triflate with a trisoxazoline (Tox) ligand led to an enantioselective transformation. The obtained cycloadducts were convenient substrates for a series of further modifications, showing the synthetic utility of these compounds. [ABSTRACT FROM AUTHOR]

Azepanes are important seven‐membered heterocycles, which are present in numerous natural and synthetic compounds. However, the development of convergent synthetic methods to access them remains challenging. Herein, we report the Lewis acid catalyzed (4+3) annulative addition of aryl and amino donor‐acceptor cyclopropanes with 2‐aza‐1,3‐dienes. Densely substituted azepane derivatives were obtained in good to excellent yields and with high diastereoselectivity. The reaction occurred under mild conditions with ytterbium triflate as the catalyst. The use of copper triflate with a trisoxazoline (Tox) ligand led to an enantioselective transformation. The obtained cycloadducts were convenient substrates for a series of further modifications, showing the synthetic utility of these compounds. [ABSTRACT FROM AUTHOR]

N-Butyl-2,3-bis(dicyclohexylamino)cyclopropenimine (1) crystallizes from benzene and hexanes in the presence of HCl as a monobenzene solvate of the hydrochloride salt, [1H]Cl⋅C6H6 or C31H54N3 +⋅Cl⋅C6H6, in the P21/n space group. The protonation of 1 results in the generation of an aromatic structure based upon the delocalization of the cyclopropene double bond around the cyclopropene ring, giving three intermediate C--C bond lengths of 1.41 A °, and the delocalization of the imine-type C--N double bond, giving three intermediate C--N bond lengths of 1.32 A °. Ion-ion and ion-benzene packing interactions are described and illustrated. [ABSTRACT FROM AUTHOR]

The ring‐opening metathesis polymerization (ROMP) of cyclopropenes using hydrazonium initiators is described. The initiators, which are formed by the condensation of 2,3‐diazabicyclo[2.2.2]octane and an aldehyde, polymerize cyclopropene monomers by a sequence of [3+2] cycloaddition and cycloreversion reactions. This process generates short chain polyolefins (Mn≤9.4 kg mol−1) with relatively low dispersities (Đ≤1.4). The optimized conditions showed efficiency comparable to that achieved with Grubbs' 2nd generation catalyst for the polymerization of 3‐methyl‐3‐phenylcyclopropene. A positive correlation between monomer to initiator ratio and degree of polymerization was revealed through NMR spectroscopy. [ABSTRACT FROM AUTHOR]

The ring‐opening metathesis polymerization (ROMP) of cyclopropenes using hydrazonium initiators is described. The initiators, which are formed by the condensation of 2,3‐diazabicyclo[2.2.2]octane and an aldehyde, polymerize cyclopropene monomers by a sequence of [3+2] cycloaddition and cycloreversion reactions. This process generates short chain polyolefins (Mn≤9.4 kg mol−1) with relatively low dispersities (Đ≤1.4). The optimized conditions showed efficiency comparable to that achieved with Grubbs' 2nd generation catalyst for the polymerization of 3‐methyl‐3‐phenylcyclopropene. A positive correlation between monomer to initiator ratio and degree of polymerization was revealed through NMR spectroscopy. [ABSTRACT FROM AUTHOR]

A facile synthesis of cyclopropenes and fluorinated cyclopropanes from readily available alkyl triflones was developed. The reaction, regardless of electronic effect, gave products in good to excellent yields and moderate diastereoselectivity. The mechanism may involve tandem Michael addition of triflones/intramolecular nucleophilic cyclization (elimination of ‐SO2CF3)/elimination of fluoride. [ABSTRACT FROM AUTHOR]

A diastereoselective synthesis of biologically interesting spirobarbiturates has been achieved via [3+2] cycloaddition of alloxan-derived azomethine ylides to 3- R -1,2-diphenylcyclopropenes. With this approach, a range of spirobarbiturate-3-azabicyclo[3.1.0]hexanes and spirobarbiturate-cyclopropa[ a ]pyrrolizines were obtained in moderate to good yields with excellent diastereoselectivities. DFT calculations (M11 density functional theory) were carried out to shed light on the molecular mechanism of 1,3-dipolar cycloaddition of alloxan-derived azomethine ylides to cyclopropenes. The cytotoxic activity of some obtained compounds against human erythroleukemia (K562) cell line was evaluated in vitro by MTS-assay. [ABSTRACT FROM AUTHOR]

The total enantioselective synthesis of (+)‐eucophylline 1 was achieved using as a key‐structural motif a chiral piperidinone bearing the natural product all‐carbon quaternary stereocenter. The elaboration of the latter is based on two strategies relying on the free‐radical carbo‐cyanation and sulfonyl‐cyanation respectively of enantiopure substituted cyclopropenes and cyclobutenes. Co‐ or Ni‐boride reduction of the nitrile functional group along with the cyclopropane and cyclobutane ring‐opening then led to the formation of the chiral piperidinone ring. Further elaboration of the latter into the key 1‐azabicyclo[3.3.1]nonane motif followed by its coupling with a 2‐cyanoaniline allowed the formation of the tetrahydrobenzo[b][1,8]‐naphthyridine skeleton of 1, which was finally accessible in 17 steps and 5.9 % overall yield from 1,1‐dibromobutene. [ABSTRACT FROM AUTHOR]

Here, a novel method for the stereoselective synthesis of alkynyl cyclopropanes, by the silver-catalyzed alkynylcyclopropanation of alkenes using alkynyl N-nosylhydrazones as alkynyl carbene precursors, is reported. This method provides a straightforward and powerful approach for preparing various alkynyl cyclopropanes in high yield with excellent stereoselectivities. In addition, the practicality of this method was demonstrated by gram-scale synthesis and late-stage modification of bioactive molecules. [ABSTRACT FROM AUTHOR]

The dearomatization of 2‐naphthols represents a simple method for the construction of complex 3D structures from simple planar starting materials. We describe a cyclopropanation of 2‐naphthols that proceeds via cyclopropene ring‐opening using rhodium and acid catalysis under mild conditions. The vinyl cyclopropane molecules were formed with high chemoselectivity and scalability, which could be further functionalized at different sites. Both computational and experimental evidence were used to elucidate the reaction mechanism. [ABSTRACT FROM AUTHOR]

The dearomatization of 2‐naphthols represents a simple method for the construction of complex 3D structures from simple planar starting materials. We describe a cyclopropanation of 2‐naphthols that proceeds via cyclopropene ring‐opening using rhodium and acid catalysis under mild conditions. The vinyl cyclopropane molecules were formed with high chemoselectivity and scalability, which could be further functionalized at different sites. Both computational and experimental evidence were used to elucidate the reaction mechanism. [ABSTRACT FROM AUTHOR]

A regio‐ and diastereoselective copper‐catalyzed carbomagnesiation of 1,2‐dialkylated cyclopropenes is reported. The regioselectivity is controlled by a subtle tethered Lewis basic moiety. The chelating moieties allow the differentiation between two electronically tantamount organometallic intermediates. Further functionalization grants access to polysubstituted stereodefined cyclopropanes bearing up to five alkyl groups. [ABSTRACT FROM AUTHOR]

A regio‐ and diastereoselective copper‐catalyzed carbomagnesiation of 1,2‐dialkylated cyclopropenes is reported. The regioselectivity is controlled by a subtle tethered Lewis basic moiety. The chelating moieties allow the differentiation between two electronically tantamount organometallic intermediates. Further functionalization grants access to polysubstituted stereodefined cyclopropanes bearing up to five alkyl groups. [ABSTRACT FROM AUTHOR]

Borylative difunctionalization of alkenes has emerged as a powerful approach for synthesizing highly functionalized molecules. Herein, dual Cu/Pd-catalysed borylfluoroallylation of alkenes was smoothly achieved by using gem-difluorinated cyclopropanes and B2pin2, providing the corresponding monofluoroalkene scaffolds in moderate to high yields with excellent stereoselectivity. Moreover, an array of synthetic building blocks can be obtained by downstream transformations. [ABSTRACT FROM AUTHOR]

β‐Aryl/alkyl vinyl diazoacetates were investigated in metallo‐vinylcarbene reactions with nitrones, revealing a Rh2(OAc)4‐catalyzed cyclopropene dimerization reaction and a copper(I) catalyzed [3+3]‐cycloaddition of nitrones. The chiral cyclopropyl‐In‐SaBox ligand with copper(I) catalysis could realize the asymmetric version of the cycloaddition reaction, delivering various 3,6‐dihydro‐1,2‐oxazine derivatives in good yield and with excellent enantioselectivity under mild conditions. [ABSTRACT FROM AUTHOR]