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Enantiomerically enriched bispiro[γ‐butyrolactone‐pyrrolidin‐4,4′‐pyrazolone] skeletons were synthesized firstly through a simple organocatalytic 1,3‐dipolar cycloaddition reaction between α‐imino γ‐lactones and alkylidene pyrazolones in high yields and excellent stereoselectivities. This efficient organocatalytic strategy provides facile access to a variety of highly functionalized drug‐like compounds with two quaternary spirocenters and should allow for structure diversification of this intriguing class of compounds. [ABSTRACT FROM AUTHOR]

Abstract: The synthesis of α‐alkylidene cyclic carbonates (αCCs) by the carboxylative coupling of CO2 with propargylic alcohols is receiving increasing interest but requires the use of catalysts that are most often added in large quantities and/or lack selectivity. Herein, we describe the fine‐tuning of the structure of organocatalysts of the ammonium‐type that enables us to identify the important structural parameters that dictate their catalytic performance. Tetrabutylammonium oxalate was revealed to be one of the most attractive organocatalysts with a remarkably fast, complete and selective production of αCCs at a low catalyst loading (2.5 mol %) under solvent‐free conditions. This study opens new avenues for the facile and selective synthesis of libraries of αCCs from CO2 and propargylic alcohol by using simple organocatalysts. [ABSTRACT FROM AUTHOR]

Various secondary alkyl iodides bearing a remote alkynylsilane underwent intramolecular carbolithiations triggered by an I/Li-exchange performed at -100 °C using t-BuLi (2.5 equiv). The resulting alkenyllithiums were stereoselectively converted to tetrasubstituted cyclopentane exo-alkylidenes. After Pd-catalyzed hydrogenation, cyclopentanes and cis-bicyclo[4.3.0]nonanes were obtained with stereocontrol of four contiguous centers. [ABSTRACT FROM AUTHOR]

An original method for the synthesis of С 5 -С 6 cyclic ketones and tetrasubstituted furans was developed based on the Cp 2 TiCl 2 -catalyzed reaction of symmetrical alkynes and α,ω-dicarboxylates in the presence of Mg and ЕtAlCl 2 . The length of the hydrocarbon chain between carboxyl groups in a,ω-dicarboxylic acid esters affects the chemoselectivity of the reaction. The formation of 2-alkylidene and 2-alkenyl cyclopent(hex)an-1-ones occurred in the reaction with esters of glutaric and adipic acids. α,ω-Dicarboxylic acid esters with more than four methylene units between carboxyl groups gave rise to substituted furans. Stereochemistry of 2-alkenyl cyclopent(hex)an-1-ones was determined based on the analysis of experimental and theoretical data obtained from DFT calculations. [ABSTRACT FROM AUTHOR]

Abstract: Unprecedented silyl‐phosphino‐carbene complexes of uranium(IV) are presented, where before all covalent actinide–carbon double bonds were stabilised by phosphorus(V) substituents or restricted to matrix isolation experiments. Conversion of [U(BIPMTMS)(Cl)(μ‐Cl)2Li(THF)2] (1, BIPMTMS=C(PPh2NSiMe3)2) into [U(BIPMTMS)(Cl){CH(Ph)(SiMe3)}] (2), and addition of [Li{CH(SiMe3)(PPh2)}(THF)]/Me2NCH2CH2NMe2 (TMEDA) gave [U{C(SiMe3)(PPh2)}(BIPMTMS)(μ‐Cl)Li(TMEDA)(μ‐TMEDA)0.5]2 (3) by α‐hydrogen abstraction. Addition of 2,2,2‐cryptand or two equivalents of 4‐N,N‐dimethylaminopyridine (DMAP) to 3 gave [U{C(SiMe3)(PPh2)}(BIPMTMS)(Cl)][Li(2,2,2‐cryptand)] (4) or [U{C(SiMe3)(PPh2)}(BIPMTMS)(DMAP)2] (5). The characterisation data for 3–5 suggest that whilst there is evidence for 3‐centre P−C−U π‐bonding character, the U=C double bond component is dominant in each case. These U=C bonds are the closest to a true uranium alkylidene yet outside of matrix isolation experiments. [ABSTRACT FROM AUTHOR]

2-Alkylidene-5-methylidene-1,3-thiazolidin-2-ylidenes react with N-bromosuccinimide to form 2-alkylidene-5-(bromomethyl)-2,3-dihydro-1,3-thiazoles, the reaction of which with S,O,N-nucleophiles is used for the selective synthesis of the corresponding 5-methylfunctionalized derivatives. [ABSTRACT FROM AUTHOR]

Ring-closing metathesis was monitored using real-time NMR of 1H hyperpolarized olefins at room temperature. By applying a selective saturation to an observable intermediate, its protons were found to transfer to ethylene. The intermediate was thus identified as a Ru-alkylidene species, which appears in the ethylene formation pathway. [ABSTRACT FROM AUTHOR]

A stereospecific three-component domino reaction between glycals, alkylidene malonate and aldehydes catalyzed by Yb(OTf)3 is described. Multi-substituted cis-fused perhydropyrano[2,3-b]pyran derivatives were obtained with high diastereoselectivity. [ABSTRACT FROM AUTHOR]

A stereospecific three-component domino reaction between glycals, alkylidene malonate and aldehydes catalyzed by Yb(OTf)3 is described. Multi-substituted cis-fused perhydropyrano[2,3-b]pyran derivatives were obtained with high diastereoselectivity. [ABSTRACT FROM AUTHOR]

Abstract: Alkylidene‐bridged scandium–copper/silver heterobimetallic complexes were synthesized and structurally characterized. The complexes contain different Sc−C and M−C (M=CuI, AgI) bonds. The reactivity of the scandium–copper heterobimetallic complex was also studied, which reveals that the heterobimetallic complex is a reaction intermediate for the transmetalation of akylidene group from ScIII to CuI. The scandium–copper heterobimetallic complex also undergoes an addition reaction with CO, resulting in the formation of a new C=C double bond. DFT calculations were used to study the bonding and the subsequent reactivity with CO of the scandium–copper heterobimetallic complex. It clearly demonstrates a cooperative effect between the two metal centers through the formation of a direct Sc⋅⋅⋅Cu interaction that drives the reactivity with CO. [ABSTRACT FROM AUTHOR]

Metal-free and environmentally friendly synthesis highly controlled by natural sources like visible light and air (or oxygen) is always a pursuit of green chemistry. In this paper, an atmosphere and light tuned highly diastereoselective synthesis of two important polyheterocyclic skeletons: cyclobuta/penta[b]indoles from aniline-tethered alkylidenecyclopropanes with alkynes, has been developed. The chiral cyclobuta/penta[b]indoles have also been obtained by optical resolution. [ABSTRACT FROM AUTHOR]

Abstract: n‐Tetrabutylammonium organic salts were used for the first time as catalysts for the coupling of CO2 with 2‐methyl‐3‐butyn‐2‐ol to form an α‐methylene cyclic carbonate. Final yields up to 98 % were reached in less than 10 h at 353 K and 3 MPa under solvent‐free conditions. A particular synergistic effect between the cation and the anion of the organocatalyst was demonstrated through catalyst screening. Online kinetic studies by Attenuated Total Reflectance (ATR) IR spectroscopy correlated to DFT calculations revealed compelling evolution of solvation of the catalyst during the reaction that provided insight into the underlying reason for the observed unique kinetics and selectivity. Such in‐depth fundamental mechanistic and kinetic studies enabled determination and comprehension of the key parameters favoring the design of novel, highly active and selective catalysts for valorization of CO2 as a chemical feedstock. [ABSTRACT FROM AUTHOR]

Abstract: A facile and efficient synthesis of 2‐oxindole derivatives bearing tetrahydropyrazine scaffold has been developed. Using water as solvent without any additional acid or metal catalyst, easy work up and high yield of products are the main advantages of this protocol. [ABSTRACT FROM AUTHOR]

On the basis of the literature data, our previous research work and docking experiments, we designed novel 19-norvitamin D compounds having elongated 2-alkylidene substituents. These 19-norcalcitriol derivatives have attached 2-(3′-aminopropylidene) substituent in which the nitrogen atom bears acyl residue derived from succinic acid and l -methionine. Both compounds were obtained by the same synthetic strategy involving Julia coupling of the A-ring ketone with the known C/D-ring sulfone. In the obtained 1α,25-dihydroxy-19-norvitamin D 3 derivative, the alkylidene substituent at C-2 was further elaborated to the desired structures. [ABSTRACT FROM AUTHOR]

Addition of one equiv of water to Mo-(CAr)[OCMe(CF3)2]3(1,2-dimethoxyethane) (2, Ar = o- (OMe)C6H4) in the presence of PPhMe2 leads to formation of Mo(O)(CHAr)[OCMe(CF3)2]2(PPhMe2) (3(PPhMe2)) in 34% yield. Addition of one equiv of water alone to 2 produces the dimeric alkylidyne hydroxide complex, {Mo(CAr)[OCMe(CF3)2]2(μ-OH)}2(dme) (4(dme)) in which each bridging hydroxide proton points toward an oxygen atom in an arylmethoxy group. Addition of PMe3 to 4(dme) gives the alkylidene oxo complex, (3(PMe3)), an analogue of 3(PPhMe2) (95% conversion, 66% isolated). Treatment of 3(PMe3) with two equiv of HCl gave Mo(O)(CHAr)Cl2(PMe3) (5), which upon addition of LiO-2,6-(2,4,6-i-Pr3C6H2)2C6H3 (LiOHIPT) gave Mo(O)(CHAr)-(OHIPT)Cl(PMe3) (6). Compound 6 in the presence of B(C6F5)3 will initiate the ring-opening metathesis polymerization of cyclooctene, 5,6-dicarbomethoxynorbor-nadiene (DCMNBD), and rac-5,6-dicarbomethoxynorbor-nene (DCMNBE), and the homocoupling of 1-decene to 9-octadecene. The poly(DCMNBD) has a cis,syndiotactic structure, whereas poly(DCMNBE) has a cis,syndiotactic,alt structure. X-ray structures were obtained for 3(PPhMe2), 4(dme), and 6. [ABSTRACT FROM AUTHOR]

The sterically encumbered NacNac ligand, [HC(MeCNAr) 2 ] − (Ar = 2,6- i- Pr 2 C 6 H 3 ), was investigated as a platform for supporting Lu-halide complexes, sought for their potential capability of being further converted into hydrocarbyl derivatives via metathetical chemistries with alkali metal alkyls. These substituted analogs were targeted as potentially viable candidates for alkane elimination chemistries, with an eye towards the formation of an isolable Lu-alkylidene fragment. [ABSTRACT FROM AUTHOR]

Abstract: Diastereoselective reactions supported by metals and nonmetals offer a multifaceted path for the synthesis of robust intermediates of value to academia and industry. The reactions that involve mono‐ and disubstituted electron‐rich and electron‐deficient olefins offer facile construction of stereogenic carbon centers. Recent advances in the development of methods and an understanding of the chemistry of oxindoles has led to approaches that provide high levels of facial control, regiocontrol and diastereoselectivity. Part I of this focus review is devoted to the chemistry of β‐monosubstituted alkylidene oxindoles. Herein, we discuss reports made over the last decade of diastereoselective reactions that involve oxindole‐containing trisubstituted alkenes, which lead to the generation of stereogenic centers and the formation carbocyclic and heterocyclic skeletons. [ABSTRACT FROM AUTHOR]

We report an unexpected rearrangement of a deprotonated picolyl-functionalized N-heterocyclic carbene (NHC) ligand from N,C-chelate to N,N-chelate in three-legged piano-stool Fe(II) and Ru(II) complexes. The reaction mechanism has been explored for one of the Fe(II) complexes. Experimental and computational studies suggest an unusual intermediate featuring a four-membered chelate ring, where the NHC and the α-carbon of one of the N-substituents coordinate to the Fe(II) center. A possible Fe-alkylidene intermediate has also been predicted by computations. [ABSTRACT FROM AUTHOR]

This review aims to offer a detailed summary of the discoveries regarding non-heteroatom-substituted alkylidenes of group 10 and 11 metals that have appeared in the literature since the first isolable representative of this class was reported in 2002. Special attention is focused on synthetic and bonding aspects of well-defined species. The importance of this family of compounds in catalytic organic transformations is often mentioned and a number of references are provided. We stress, however, that it is not the main issue of this review, as this topic has received considerable attention in the current literature. [ABSTRACT FROM AUTHOR]

The vinyliminium complexes [Fe2{μ-η1:η3-C(CO2Me)C(H)CN(Me)(R)}(μ-CO)(CO)(Cp)2][SO3CF3] [R = Me, 1a; R = 4-C6H4OMe, 1b; R = CH2Ph, 1c] react with primary amines (NH2R′; R′= Me, Et, Bun, (CH2)2NH2, CH2Ph) and ammonia to give the corresponding bridging amidine-alkylidene complexes [Fe2{μ-κ1(N):η1(C):η1(C)-C(CO2Me)CH2C{N(Me)(R)}(NR′)}(μ-CO)(CO)(Cp)2] (4a-j) in 70-90% yields. Likewise, the vinyliminium complex [Fe2{μ-η1:η3-C(CO2Me)C(CO2Me)CN(Me)2}(μ-CO)(CO)(Cp)2][SO3CF3] (1d) reacts with NH2R′ (R′= Me, Et) to form the corresponding amidine-alkylidene [Fe2{μ-κ1(N):η1(C):η1(C)-C(CO2Me)CH(CO2Me)C(NMe2)(NR′)}(μ-CO)(CO)(Cp)2] [R′= Me, 8a; R′ = Et, 8b], generating selectively one of the two diastereoisomers associated with the presence of the methylidene unit −CH(COO2Me)- within the bridging ligand. Amination of the vinyliminium complexes 1a-c takes place also with hydrazine, resulting in the formation of [Fe2{μ-κ1(N):η1(C):η1(C)-C(CO2Me)CH2C{N(Me)(R)}(NNH2)}(μ-CO)(CO)(Cp)2] [R = Me, 5a; R = 4-C6H4OMe, 5b; R = CH2Ph, 5c]. Complexes 1b and 1d react with NHMe2, affording the en-(1,1)diamino-alkylidene complexes [Fe2{μ-η1:η3-C(CO2Me)C(R′)C(NMe2)N(Me)(R)}(μ-CO)(CO)(Cp)2] [R = 4-C6H4OMe, R′ = H, 9b; R = Me, R′ = CO2Me, 9d]. The reaction of 1c with piperidine results in formation of the amidine-alkylidene [Fe2{μ-κ1(N):η1(C):η1(C)-C(CO2Me)CH2C{N(Me)(CH2Ph)}(CH2CH2CH2CH═CH2)}(μ-CO)(CO)(Cp)2] (10), which implies piperidine ring-opening. All the products have been purified by alumina chromatography and characterized by analytical and spectroscopic methods; in addition, the molecular structures of 4f, 5b, and 8a have been ascertained by X-ray diffraction studies. [ABSTRACT FROM AUTHOR]

An efficient diastereoselective synthesis of substituted piperidines is accomplished by using catalytic amount of FeCl 3 ·6H 2 O via intramolecular aza-Michael addition of carbamate on alkylidene β -keto (L)-menthyl esters in a very short time. [ABSTRACT FROM AUTHOR]

One-pot multi-component synthesis of N,N′-alkylidene bisamides, 2,4,5-trisubstituted imidazoles and 1,2,4,5-tetrasubstituted imidazoles in the presence of catalytic material heteropoly-11-tungsto-1-vanadophosphoric acid (HPV) supported on activated natural clay for about 20% (HPVAC-20) under solvent-free reaction condition have been achieved. Green heterogeneous reaction condition, simple workup procedure, short reaction time, high yield of products, and reusability of the catalyst are the advantages of this protocol. [ABSTRACT FROM AUTHOR]

The reaction of [W(N-2,6-iPr2C6H3)(CHCMe2Ph)(OTf)2(DME)] (DME = 1,2-dimethoxyethane, OTf = CF3SO3) with the N-heterocyclic carbene (NHC) 1,3-bis(2,4,6-trimethylphenyl)imidazolidin-2-ylidene (IMesH2) leads to DME activation followed by transmethylation and in due consequence to the formation of the N-heterocyclic olefin complex [W(N-2,6-iPr2C6H3)(CHCMe2Ph)(OTf)2(IMesH2CH2)] along with [W(N-2,6-iPr2C6H3)(CHCMe2Ph)(OTf)(IMesH2)(κ2-O(CH2)2OMe)], [1,3-bis(2,4,6-trimethylphenyl)-2-methylimidazolidinium+ (OTf−)] and [1,3-bis(2,4,6-trimethylphenyl)-2-H-imidazolidinium+ (OTf−)]. A reaction pathway is proposed and confirmed by the use of 13C-labelled compounds; structures of the products were verified by NMR and/or single-crystal X-ray analysis. [ABSTRACT FROM AUTHOR]

Reactions between Mo(N-t-Bu)2(CH2-t-Bu)2 or Mo(NAdamantyl)2(CH2CMe2Ph)2 and 3 equiv of HCl in the presence of 1 equiv of PPh2Me yield Mo(NR)(CHR')(PPh2Me)Cl2 complexes, from which Mo(NR)(CHR')(PPh2Me)(OAr)Cl complexes (OAr = a 2,6-terphenoxide) can be prepared. The Mo(NR)(CHR')(PPh2Me)(OAr)Cl complexes were evaluated as cross-metathesis catalysts between cyclooctene and Z-1,2-dichloroethylene. The efficiencies of the test reaction for complexes in which OAr = OTPP, OHMT, OHIPT, or OHTBT (where OTPP is 2,3,5,6-tetraphenylphenoxide, OHMT is hexamethylterphenoxide, OHIPT is hexaisopropylterphenoxide, and OHTBT is hexa-t-butylterphenoxide) maximize when OAr is OHMT or OHIPT. Mo(N-t-Bu)(CH-t-Bu)(PPh2Me)Cl2 is essentially inactive for the reaction between cyclooctene and Z-1,2-dichloroethylene. X-ray structural studies were carried out on Mo(NAd)(CHCMe2Ph)(PPh2Me)Cl2, Mo(N-t-Bu)(CH-t-Bu)(PPh2Me)(OHMT)Cl, Mo(NAd)(CHCMe2Ph)(Cl)(OHTBT)(PMe3), and [Mo(NAd)(CHCMe2Ph)(PMe3)(Cl)]2(μ-O), the product of the reaction between Mo(NAd)(CHCMe2Ph)(Cl)(OHTBT)(PMe3) and 0.5 equiv of water. [ABSTRACT FROM AUTHOR]

Cyanophosphates (CPs) can easily be prepared via the reactions of carbonyl compounds with diethyl phosphorocyanidate (DEPC) in the presence of LiCN (cat.) under non-aqueous conditions. Treatment of ketone-derived CPs with TMSN 3 /Bu 2 SnO (cat.) in toluene at reflux produces cyclopentenes or heterocyclic products in good yields under neutral conditions. In this two-step transformation, CPs may form tetrazolylphosphates, which subsequently undergo successive fragmentation to generate alkylidene carbenes, which undergo [1,5]-C–H insertions to yield five membered compounds. [ABSTRACT FROM AUTHOR]

A series of prenyl-containing malonates are kinetically benchmarked against the standard allyl-containing congeners using a ruthenium benzylidene precatalyst for ring-closing metatheses. The prenyl grouping is found to be a superior acceptor olefin compared to an allyl group in RCM processes with ruthenium alkylidenes derived from terminal alkenes. The prenyl group is also found to be a highly competent acceptor for a ruthenium alkylidene derived from a 1,1-disubstituted olefin in a RCM process. [ABSTRACT FROM AUTHOR]

ABSTRACT Ring opening metathesis polymerizations (ROMP) of norbornene (NBE), tetracyclododecene (TCD) in the presence of cis-cyclooctene (COE) using vanadium-alkylidene catalyst, V(CHSiMe3)(N-2,6-Cl2C6H3)(OC6F5)(PMe3)2 ( 1), were explored. The polymerizations with TCD afforded high-molecular-weight polymers ( Mn = 19,500-47,400) with low PDI ( Mw/ Mn) values (1.18-1.38) which possess microstructure of repeated ring-opened TCD and certain methylene units by incorporation of ring-opened COE on the basis of microstructure analysis by NMR spectra and DSC thermograms; hydrogenated copolymer possessed melting temperature at 294 °C. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 3067-3074 [ABSTRACT FROM AUTHOR]

We describe an unusual net [2+2] cycloaddition reaction between boron alkylidenes and unactivated alkenes. This reaction provides a new method for the construction of carbocyclic ring systems bearing versatile organoboronic esters. Aside from surveying the scope of this reaction, we provide details about the mechanistic underpinnings of this process, and examine its application to the synthesis of the natural product aphanamal. [ABSTRACT FROM AUTHOR]

An efficient and expedient route to the synthesis of dicarba peptides from protecting group-free sequences is reported using Ru-alkylidene catalysed olefin metathesis. A range of cyclic peptides was prepared from linear peptides containing two Z-crotyl glycine residues. Free amine groups were masked as salts with Brønsted acids preventing in situ catalyst decomposition. Excellent RCM conversion was obtained in both DMF and methanol. [ABSTRACT FROM AUTHOR]

Reactions of (cyclopentadienylidenehydrazono)triphenylphosphorane with RuCl2(PPh3)3 or (η6-cymene)RuCl2(PPh3) in toluene produced the chlorocyclopentadienyl complex (η5-C5H4Cl)RuCl(PPh3)2, which was likely formed through the cyclopentadienylidene intermediate RuCl2{C(C4H4)}(PPh3)2. Treatment of (η6-cymene)RuCl2(PPh3) with (cyclopentadienylidenehydrazono)triphenylphosphorane in methanol gave [(η5-C5H4Cl)Ru(η6-cymene)]+. Computational studies reveal that the thermodynamic stability of the analogous chlororuthenium complexes RuCl2(CRR')(PPh3)2 and [RuCl(CRR')(PMe3)(η6-C6H6)]+, with respect to the formation of the corresponding η5-chloropentadienyl complexes via a migratory carbene-insertion reaction is in the order of cyclopentadienylidene < indenylidene < fluorenylidene < phenylcarbene. [ABSTRACT FROM AUTHOR]

O-Alkyl derivatives of naringenin (1a-10a) were prepared from naringenin using the corresponding alkyl iodides and anhydrous potassium carbonate. The resulting products were used to obtain oximes (1b-10b). All compounds were tested for antimicrobial activity against Escherichia coli ATCC10536, Staphylococcus aureus DSM799, Candida albicans DSM1386, Alternaria alternata CBS1526, Fusarium linii KB-F1, and Aspergillus niger DSM1957. The resulting biological activity was expressed as the increase in optical density (ΔOD). The highest inhibitory effect against E. coli ATCC10536 was observed for 7,4'-di-O-pentylnaringenin (8a), 7-O-dodecylnaringenin (9a), naringenin oxime (NG-OX), 7,4'-di-O-pentylnaringenin oxime (8b), and 7-O-dodecylnaringenin oxime (9b) (ΔOD = 0). 7-O-dodecylnaringenin oxime (9b) also inhibited the growth of S. aureus DSM799 (ΔOD = 0.35) and C. albicans DSM1386 (ΔOD = 0.22). The growth of A. alternata CBS1526 was inhibited as a result of the action of 7,4'-di-O-methylnaringenin (2a), 7-O-ethylnaringenin (4a), 7,4'-di-O-ethylnaringenin (5a), 5,7,4'-tri-O-ethylnaringenin (6a), 7,4'-di-O-pentylnaringenin (8a), and 7-O-dodecylnaringenin (9a) (ΔOD in the range of 0.49-0.42) in comparison to that of the control culture (ΔOD = 1.87). In the case of F. linii KB-F1, naringenin (NG), 7,4'-di-O-dodecylnaringenin (10a), 7-O-dodecylnaringenin oxime (9b), and 7,4'-di-O-dodecylnaringenin oxime (10b) showed the strongest effect (ΔOD = 0). 7,4'-Di-O-pentylnaringenin (8a) and naringenin oxime (NG-OX) hindered the growth of A. niger DSM1957 (ΔOD = 0). [ABSTRACT FROM AUTHOR]

Remote carbon-hydrogen activation on titanium dinuclear complexes [{Ti(η5-C5Me5)R2}2(μ-O)] [R = CH2SiMe3 2, CH2CMe3 3, and CH2Ph 5) have been examined both synthetically and theoretically. While the thermal treatment of the oxoderivative [{Ti(η5-C5Me5)(CH2SiMe3)2}2(μ-O)] (2) led to a series of metallacycle complexes (2a-c) by sequential carbon-hydrogen activation processes, [{Ti(η5-C5Me5)(CH2CMe3)2}2(μ-O)] (3) gave rise to the formation of the metallacycle tuck-over species [Ti2(η5-C5Me5)(μ-η5-C5Me4CH2-κC)(CH2CMe3)(μ-CH2CMe2CH2)(μ-O)] (4), as result of hydrogen abstraction from a η5-C5Me5 ligand. However, the thermolysis of the tetrabenzyl complex [{Ti(η5-C5Me5)(CH2Ph)2}2(μ-O)] (5) yielded the derivative [Ti2(η5-C5Me5)(μ-η5-C5Me4CH2-κC)(CH2Ph)3(μ-O)] (6) that only exhibits tuck-over η5-C5Me5 metalation. DFT calculations show that the mechanism involves a first α-hydrogen abstraction to generate a transient titanium alkylidene, which enables it to activate β- and γ-C(sp³)-H bonds on the adjacent titanium center. The calculations also establish a reactivity order for the different type of γ-H abstractions, trimethylsilyl > neopentyl ≌ benzyl, allowing us to explain the observed selectivity. [ABSTRACT FROM AUTHOR]

Described is a robust platform for the synthesis of a large diversity of novel functional CO2-sourced polymers by exploiting the regiocontrolled ring-opening of α-alkylidene carbonates by various nucleophiles. The reactivity of α-alkylidene carbonates is dictated by the exocyclic olefinic group. The polyaddition of CO2-sourced bis(α-alkylidene carbonate)s (bis-αCCs) with primary and secondary diamines provides novel regioregular functional poly(urethane)s. The reactivity of bis-αCCs is also exploited for producing new poly(β-oxo-carbonate)s by organocatalyzed polyaddition with a diol. This synthesis platform provides new functional variants of world-class leading polymer families (polyurethanes, polycarbonates) and valorizes CO2 as a chemical feedstock. [ABSTRACT FROM AUTHOR]

Conspectus N-Heterocyclic olefins (NHOs) have gone from the topic of a few scattered (but important) reports in the early 1990s to very recently being a ligand/reagent of choice in the far-reaching research fields of organocatalysis, olefin and heterocycle polymerization, and low oxidation state main group element chemistry. NHOs are formally derived by appending an alkylidene (CR2) unit onto an N-heterocyclic carbene (NHC), and their pronounced ylidic character leads to high nucleophilicity and soft Lewis basic character at the ligating carbon atom. These olefinic donors can also be structurally derived from imidazole, triazole, and thiazole-based heterocyclic carbenes and, as a result, have highly tunable electronic and steric properties. In this Account, we will focus on various synthetic routes to imidazole-2-ylidene derived NHOs (sometimes referred to as deoxy-Breslow intermediates) followed by a discussion of the electron-donor ability of this structurally tunable ligand group. It should be mentioned that NHOs have a close structural analogy with Breslow-type intermediates, N-heterocyclic ketene aminals, and β-azolium ylides; while these latter species play important roles in advancing synthetic organic chemistry, discussion in this Account will be confined mostly to imidazole-2-ylidene derived NHOs. In addition, we will cover selected examples from the literature where NHOs and their anionic counterparts, N-heterocyclic vinylenes, are used to access reactive main group species not attainable using traditional ligands. Added motivation for these studies comes from the emerging number of low coordinate main group element based compounds that display reactivity once reserved for precious metal complexes (such as H-H and C-H bond activation). Moreover, NHOs are versatile precursors to new mixed element (P/C and N/C), and potentially bidentate, ligand constructs of great potential in catalysis, where various metal oxidation states and coordination environments need to be stabilized during a catalytic cycle. The most active area of recent growth for NHOs is their use as nucleophiles to promote efficient organocatalytic transformations, including transesterification, carbonyl reduction, and the conversion of CO2 into value added products. Polyesters have also been generated through the NHO-promoted ring-opening polymerization of lactones, and the highly tunable nature of NHO organocatalysts allows for the rapid screening and enhancement of catalytic performance. Therefore, the growing utility of NHOs in the realm of organic and polymer chemistry can be viewed as evidence of the widespread impact of N-heterocyclic olefins on the chemical community. It is hoped that through this Account others will join this flourishing research domain and that the rapid recent growth of NHO chemistry is sustained for the foreseeable future. [ABSTRACT FROM AUTHOR]

The synthesis of W(NAr′)(NHC)(=CHR)(2,5-Me2pyr)2 ( 1; Ar′: 2,6- iPr2C6H3; NHC: 1,3-diisopropylimidazol-2-ylidene; 2,5-Me2pyr: 2,5-dimethylpyrrolide; R: CMe2Ph), W(NAr′)(NHC)(=CHR)(2,5-Me2pyr)(OC6F5) ( 2), W(NAr′)(NHC)(=CHR)(OSiPh3)2 ( 3), [W(NAr′)(NHC)(=CHR)(OSiPh3))(MeCN)+][B(ArF)4−] ( 4; B(ArF)4−: B(3,5-(CF3)2C6H3)4−), [W(NAr′)(NHC)(=CHR)(2,5-Me2pyr))+][B(ArF)4−] ( 5), [W(NAr′)(NHC)(=CHR)(OC6F5))( tBuCN)+][B(ArF)4−] ( 6), W(NAr′)(NHC)(=CHR)(O tBu)2 ( 7), [W(NAr′)(NHC)(=CHR)(O tBu)+][B(ArF)4−] ( 8), and W(NAr′)(NHC)(=CHR)(OCMe(CF3)2)2 ( 9) is described, and the reactivity of the complexes in olefin metathesis and cyclopolymerization is reported. The cationic complexes 4, 5, and 6 showed high productivity and activity in olefin metathesis reactions, with turnover numbers of up to 40 000 and turnover frequencies (TOF5min) of up to 31 s−1, and also substantial functional group tolerance toward esters, nitriles, alcohols, and sulfides, particularly in the cyclopolymerization of α,ω-diynes. [ABSTRACT FROM AUTHOR]

Cooperative catalysis has contributed greatly to the progress of asymmetric synthesis. However, double-activation catalysis has been less explored, especially for covalently tethered species. Here, we present a double-activation strategy for α′-alkylidene cyclic enone substrates that uses a chiral primary amine and 2-mercaptobenzoic acid to promote regio- and chemoselective addition to generate the complex interrupted iminium ion species. Significantly enhanced reactivity and enantioselectivity were observed for β-regioselective Michael addition and Friedel-Crafts alkylation with malononitriles and indoles, respectively, which produced a spectrum of chiral cyclic adducts with an exo-alkylidene group. Moreover, a HRMS study detected a few key covalently tethered intermediates among the substrates and catalysts, which helped elucidate the catalytic mechanism. [ABSTRACT FROM AUTHOR]

3-Substituted oxindoles are very interesting molecules both for their potential biological activity and for their role as starting materials toward more complex oxindole-based structures. These molecules can be prepared by the reduction of a 3-ylidene oxindole precursor by classical metal-catalysed chemical reductions of the olefin. In this work we present a biocatalytic approach for the reduction of oxindole-based olefins using baker's yeast. All the substrates were efficiently reduced in high yields. When an α,β-unsaturated ketone was used, the corresponding saturated alcohol was obtained in high yield and ee. To further investigate the enzyme-substrate interactions a molecular docking study was also performed. [ABSTRACT FROM AUTHOR]

Inspired by recent reports of low-valent iron-complex-catalyzed formal [2+2] cycloaddition of olefins, we demonstrate computationally that with such low-valent iron complexes and with 'strong' ligands, the olefin metathesis is also preferred over the undesired cyclopropanation side-reaction, competition already studied by Hoffmann and co-workers almost 40 years ago ( J. Am. Chem. Soc. 1981, 103, 5582). The [2+2] cycloaddition step in metathesis propagation, which gives a Chauvin-type metallacyclobutane intermediate, is proposed to proceed either via a planar four-electron Craig-Möbius aromatic [π2s+π2s] transition-state structure with a low barrier of 4.7 kcal mol−1 or, alternatively, via a twisted Zimmerman-Möbius aromatic [π2s+π2a] transition state with a 5.5 kcal mol−1 activation-energy barrier, with respect to an 'encounter' π-complex minimum obtained from an FeII alkylidene and the entering olefin, while the corresponding triplet pathways are all disfavored. [ABSTRACT FROM AUTHOR]

Controlled vinylogous carbon-carbon bond-forming reactions are useful options for providing the selective remote functionalization of conjugated carbonyl substrates. Remotely enolizable alkylidene heterocyclic and carbocyclic carbonyl compounds are pronucleophilic substrates that may be engaged in highly valuable chemical transformations. This review emphasizes the merits of these recently discovered vinylogous donors in the chemo-, regio- and stereoselective synthesis of many functionality-rich products. 1 Introduction 2 Alkylidene Oxindoles 3 Alkylidene Pyrazolinones 4 Alkylidene Furanones 5 Alkylidene Azlactones 6 Cycloalkylidene Carbonyl Compounds 7 Alkylidene Indenones 8 Cycloalkylidene Malononitriles 9 Conclusion [ABSTRACT FROM AUTHOR]

This tutorial explores the major pathways of forming metal-carbon double bonds in high-oxidation-state alkylidene complexes that began with the alkylidene chemistry of tantalum complexes in the 1970s and continued with the organometallic chemistry of Mo, W, and Re and the development of homogeneous catalysts for the metathesis of olefins. It also explores recent findings in surface organometallic chemistry and discusses the link between molecularly defined and heterogeneous catalysts. Recent results suggest that heterogeneous olefin metathesis catalysts that are activated toward metathesis upon exposure to olefins produce a d0 alkylidene through formation of a metallacyclopentane ring at d² metal sites followed by "a ring contraction" to a metallacyclobutane, a reaction that was first observed in tantalum chemistry. [ABSTRACT FROM AUTHOR]

A bis(cycloocta-1,5-diene)nickel-catalyzed highly regio- and ( E)-stereoselective hydrocarboxylation of 2-alkynylanilines under very mild conditions has been developed to afford ( E)-[2-( o-aminophenyl)]acrylic acids, which could easily be converted to ( E)-3-alkylidene-2-indolinones with important potential bioactivity. The stereoselective syntheses of two biologically active molecules, ( E)-3-benzylidene-2-indolinone (chemo-preventive potential in inducing NQO1 activity) and ( E)-3-(3-methylbutylidene)-2-indolinone (a natural product isolated from Cimicifuga foetida with cytotoxic activity against HL-60 cells) are presented as examples. [ABSTRACT FROM AUTHOR]

Ionic Mo- and W-imido alkylidene N-heterocyclic carbene (NHC) olefin metathesis catalysts, [Mo{ N-2,6-(Me2)C6H3}(CHCMe2Ph)(IMesH2)(OTf)(PPS)]OTf ( 3), [Mo( N-2,6-(Me2)C6H3)(CHCMe2Ph)(IMesH2)(OC6F5)(PPS)][B(ArF)4] ( 5), [Mo(N tBu)(CHCMe2Ph)(4,5-dichloro-1,3-dimethylimidazol-2-ylidene)(OTf)(2,6-Ph-4-{2,4,6-Ph-pyridinium}phenolate)][OTf] ( 9), [Mo(N tBu)(CHCMe2Ph)(4,5-dichloro-1,3-dimethylimidazol-2-ylidene)(2,6-Ph-4-{2,4,6-Ph-pyridinium}phenolate)][B(ArF)4]2 ( 10, PPS=pyridiniumpropanesulfonate, IMesH2=1,3-dimesitylimidazolin-2-ylidene, OTf=CF3SO3, B(ArF)4=tetrakis(3,5-bis(trifluoromethyl)phenyl)borate) were prepared from betaine-type ligands. Also, the first bis-NHC and a nitron-based bis(amido) bistriflate imido alkylidene complex, [Mo(N tBu)(CHCMe2Ph)(4,5-dichloro-1,3-dimethylimidazol-2-ylidene)2(THF)(2,6-Ph-4-{2,4,6-Ph-pyridinium}phenolate)][OTf]2 ( 11) and [Mo( N-2,6-Me2-C6H3)(CHCMe2Ph)( N-{1,4-diphenyl-1,3,4-triazol-2-ylium}- N-phenyl-amido)2][OTf]2 ( 14) along with ionic [W( N-2,6- iPr2-C6H3)(CHCMe2Ph)( N-2,5-Me2C4H2)(I iPr)(2,6- tBu-4-PPh3-phenolate)] (17, I iPr=1,3-diisopropylimidazol-2-ylidene) are reported. With these new catalysts, the first biphasic reaction setup with Group 6 metal alkylidene NHC complexes was successfully established using a pyrrole/heptane mixture as a liquid phase. Productivities under biphasic conditions were comparable to those of reactions in 1,2-dichloroethane or toluene. Metal concentrations of <2 ppm migrated into the nonpolar heptane phase as measured by inductively coupled plasma-optical emission spectroscopy. [ABSTRACT FROM AUTHOR]

A series of ( Z)-methyl 2( Z)-3-substituted-2-(cycloalkylidenehydrazono)-4-oxothiazolidin-5-ylidene)-acetate derivatives were synthesized via condensation alkylidene- N-substituted hydrazinecarbothioamides with dimethyl acetylenedicarboxylate. The synthesized compounds were characterized by using different spectroscopic methods and confirmed by single crystal X-ray analysis. The behavior of (cyclic-alkylidene) hydrazinecarbothioamides in cyclization was presented. The mechanism of transformation of ( Z)-methyl 2-(( Z)-3-(cyclopentylideneamino)-4-oxo-2-(phenylimino)thiazolidin-5-ylidene)acetate ( 14) into the more stable ( Z)-Methyl 2-[( Z)-2-(cyclopentylidenehydrazono)-4-oxo-3-phenylthiazolidin-5-ylidene]acetate ( 5a) was discussed and confirmed. [ABSTRACT FROM AUTHOR]

Transition-metal alkylidenes are important reactive organometallic intermediates, and our current knowledge on them has been mainly restricted to those with closed-shell electronic configurations. In this study, we present an exploration on open-shell iron alkylidenes with a weak-field tripodal amido-phosphine-amido ligand. We found that a high-spin (amido-phosphine-amido)iron(II) complex can react with (p-tolyl)2CN2 to afford a high-spin (amido-ylide-amido)iron(II) complex, 2, which could transfer its alkylidene moiety to a variety of alkenes, either the electron-rich or electron-deficient ones, to form cyclopropane derivatives. The reaction of 2 with cis-β-deuterio-styrene gave deuterated cyclopropane derivatives with partial loss of the stereochemical integrity with respect to the cis-styrene. Kinetic study on the cyclopropanation reaction of 2 with 4-fluoro-styrene disclosed the activation parameters of ΔH⧧ = 23 ± 1 kcal/mol and ΔS⧧ = -20 ± 3 cal/mol/K, which are comparable to those of the cyclopropanation reactions involving transition-metal alkylidenes. However, the cyclopropanation of para-substituted styrenes by 2 shows a nonlinear Hammett plot of log(kX/kH) vs σp. By introduction of a radical parameter, a linear plot of log(kX/kH) vs 0.59σp + 0.55σc• was obtained, which suggests the "nucleophilic" radical nature of the transition state of the cyclopropanation step. In corroboration with the experimental observations, density functional theory calculation on the reaction of 2 with styrene suggests the involvement of an open-shell (amido-phosphine-amido)iron alkylidene intermediate that is higher in energy than its (amido-ylide-amido)iron(II) precursor and an "outer-sphere" radical-type mechanism for the cyclopropanation step. The negative charge distribution on the alkylidene carbon atoms of the open-shell states (S = 2 and 1) explains the high activity of the cyclopropanation reaction toward electron-deficient alkenes. The study demonstrates the unique activity of open-shell iron alkylidene species beyond its closed-shell analogues, thus pointing out their potential synthetic usage in catalysis. [ABSTRACT FROM AUTHOR]

A palladium-catalyzed, three-component reaction between propargylic alcohols, CO2, and aryl halides was developed whereby a sequential carboxylation, trans-oxopalladation of the C C bond by an ArPdX species, and a reductive elimination procedure afforded a series of functionalized α-alkylidene cyclic carbonates in moderate to excellent yields. Notably, the configuration of these tetrasubstituted olefins was dominated by the trans-oxopalladation step where the aryl group derived from ArX is located trans to the oxygen attached in the double bond. This protocol features simultaneous formation of four novel bonds in a one-pot reaction, representing an efficient method for incorporation of CO2 into heterocycles. [ABSTRACT FROM AUTHOR]

Facile and convenient synthesis of α,β -unsaturated esters and thioesters from alkylidene derivatives of Meldrum’s Acid is described. This method uses catalytic amount of FeCl 3 ·6H 2 O (0.001–0.005 equiv) with alcohols/thiols (1 equiv) in dry CH 3 NO 2 followed by catalytic amount of piperidine. A variety of α,β -unsaturated esters and thioesters have been synthesized with high E -stereoselectivity in good to excellent yields. The application of this methodology is demonstrated by gram scale synthesis of octinoxate, a sunscreen agent, and other p -methoxycinnamate esters. [ABSTRACT FROM AUTHOR]