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Carlos Saá - One of the best experts on this subject based on the ideXlab platform.
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Cp*RuCl‐Vinyl Carbenes: Two Faces and the Bifunctional Role in Catalytic Processes
Chemistry (Weinheim an der Bergstrasse Germany), 2020Co-Authors: Damián Padín, Jesús A. Varela, Carlos SaáAbstract:Ruthenium Vinyl Carbenes derived from Cp/Cp*RuCl-based complexes (Cp=cyclopentadiene, Cp*=1,2,3,4,5-pentamethylcyclopentadiene) have been routinely invoked as key intermediates in tandem reactions involving a Carbene/alkyne metathesis (CAM). A priori, these intermediates resemble the Grubbs-type family of catalysts, but they exhibit a completely different reactivity pattern that few, if any, other catalytic system can reproduce so far. The reactivity of these species with α-unsubstituted and α-substituted alkynals showcases the peculiarities of these intermediates. Although Z-Vinyl dihydrooxazines are preferentially obtained with the former, Z-Vinyl epoxypyrrolidines are obtained with the latter. A combination of spectroscopic and computational data now prove that a η3 -coordination mode of the ruthenium Vinyl Carbene and the presence of a Lewis basic chloride ligand give rise to two markedly different stereoelectronic faces, which are responsible for the unconventional reactivity of these species.
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Recent Advances in Ruthenium-Catalyzed Carbene/Alkyne Metathesis (CAM) Transformations
Synlett, 2020Co-Authors: Damián Padín, Jesús A. Varela, Carlos SaáAbstract:Carbene intermediates have shown versatile applications in modern synthetic chemistry. Catalytic ruthenium Carbene/alkyne metathesis (CAM) with readily available substrates renders an efficient procedure for the in situ generation of ruthenium Vinyl Carbene intermediates. Here, recent advances in synthetic applications of ruthenium-catalyzed Carbene/alkyne metathesis (CAM) are highlighted. 1 Introduction 2 Ruthenium Vinyl Carbenes through Carbene/Alkyne Metathesis (CAM) 3 Nonpolar Transformations of Ruthenium Vinyl Carbenes 4 Polar Transformations of Ruthenium Vinyl Carbenes 4.1 Intramolecular Ruthenium-Catalyzed [1,5]- and [1,6]-Hydride Transfer/Cyclization 4.2 Heterocyclizations of Alkynals and Alkynones 4.3 Heterocyclizations of ortho-(Alkynyloxy)benzylamines 5 DFT Studies on the Stereoselectivity of the CAM Reaction 6 Conclusions
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[2 + 1] Cycloaddition of Catalytic Ruthenium Vinyl Carbenes: A Stereoselective Controlled Access to (Z)- and (E)-Vinyl Epoxypyrrolidines
ACS Catalysis, 2016Co-Authors: Damián Padín, Fermín Cambeiro, Martin Fananas‐mastral, Jesús A. Varela, Carlos SaáAbstract:Aza-alkynals undergo a cyclization reaction with diazo compounds in the presence of catalytic amounts of Cp*RuCl(cod) to afford Vinyl epoxypyrrolidines, valuable building blocks for the synthesis of biologically active molecules. Ruthenium Vinyl Carbene intermediates have been invoked to explain the overall [2 + 1] cycloaddition (epoxy-annulation reaction). The reaction proceeds under mild conditions and in short reaction times (5–80 min) with complete (Z)- or (E)-stereoselectivity on the Vinyl substituent, depending on the nature of the diazo compound used. Theoretical calculations support a mechanistic rationale to explain this controlled process.
William D. Wulff - One of the best experts on this subject based on the ideXlab platform.
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Synthesis of [m.n]Cyclophanes: Regiochemistry Transfer from Vinyl Halides to Cyclophanes via Fischer Carbene Complexes
Chemistry (Weinheim an der Bergstrasse Germany), 2013Co-Authors: Huan Wang, Alexander V. Predeus, William D. WulffAbstract:The double benzannulation of bis-Carbene complexes of chromium with a,w-diynes generates (m.n)cyclo- phanes in which all three rings are gen- erated in a single reaction. This triple annulation process is very flexible al- lowing for the construction of symmet- rical (n.n)cyclophanes and unsymmetri- cal (m.n)cyclophanes as well as isomers in which the two benzene rings are both meta bridged or both para bridg- ed, and isomers that contain both meta and para bridges. The connectivity pat- terns of the bridges in the cyclophanes can be controlled by regioselectivity transfer from the bis-Vinyl Carbene complexes in which the substitution pattern of the Vinyl groups in the car- bene complexes dictate the connectivi- ty pattern in the (m.n)cyclophanes. This synthesis of (n.n)cyclophanes is quite flexible with regard to ring size and can be used with tether lengths ranging from n = 2t on = 16 and thus to ring sizes with up to 40 member rings. The only limitation to regioselectivity trans- fer from the Carbene complexes to the (m.n)cyclophanes was found in the syn- thesis of para,para-cyclophanes with four carbon tethers for which the loss of fidelity occurred with the unexpect- ed formation of meta,para-cyclophanes.
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The First Examples of a Meta-Benzannulation from the Reaction of Fischer Carbene Complexes with Alkynes
Journal of the American Chemical Society, 2003Co-Authors: Huan Wang, William D. Wulff, Jie Huang, Arnold L. RheingoldAbstract:The intramolecular benzannulations of Carbene complexes with alkynes are examined where the alkyne is tethered to the α-carbon of the Vinyl Carbene complex. These reactions are sensitive to the length of the tether and to the nature of the solvent. With a tether length of 16 methylenes, the reaction occurs in the same fashion as the intermolecular reactions to give a p-cyclophane. With intermediate tether lengths (n = 10, 13), the reaction gives an additional p-cyclophane in which the two oxygen substituents are meta on the arene ring. This type of product is unprecedented from the reaction of Carbene complexes and alkynes and is quite surprising because the formation of this product requires that the carbon−carbon bond between the α- and β-carbons of the Vinyl Carbene complex is broken. A mechanism is proposed to account for this process which involves the crossed intramolecular [2 + 2] cycloaddition of the alkene and a ketene in a conjugated dienyl ketene to give a benzvalenone paddalane intermediate.
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Electronic Tuning of Fischer Carbene Complexes in the Preparation of Bicyclo[3.1.1]heptanones as Taxane A-ring Synthons
Tetrahedron, 2000Co-Authors: Weiqin Jiang, Michael J. Fuertes, William D. WulffAbstract:Abstract A synthetic route to taxol and other Taxus diterpenes is described which employs as a key step the reaction between a Fischer Carbene complex and a 1,6 enyne to construct 1-substituted-7,7-dimethyl-2-methylenebicyclo[3.1.1]heptan-6-ones. It was found that the reaction between complex 2 and 7-methyl-3-methylene-6-octen-1-yne (dienyne 30) yielded a mixture of bicyclo[3.1.1]heptanone 35 and cyclobutenone 36, the latter possibly arising from the migration of the chromium fragment from an electron-rich alkene to a less electron-rich alkene in the Vinyl Carbene complex intermediate (i.e. 40–42). On this basis, it was expected that bicycloheptanone yields would increase with increasing electron deficiency in the intermediate 40 since this should lead to more competitive CO insertion. This was observed with a series of electronically modified Carbene complexes (45 and 48a–d). The more electron deficient complexes gave good yields of bicycloheptanones, thus providing an efficient means for preparing taxane A-ring synthons.
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mechanistic studies on the reaction of fischer Carbene complex with alkynes does the alkyne insertion intermediate form irreversibly
Journal of the American Chemical Society, 1999Co-Authors: Marcey L. Waters, Mary Ellen Bos, William D. WulffAbstract:The regioselectivity of the formation of three different products from the reaction of 1-phenylpropyne with (methoxy)(2-methoxyl-1-phenyl)methylene pentacarbonyl chromium 12 was examined in detail. The phenol product is formed with a substantial regioselectivity which is temperature-dependent, but the indene products (obtained as two compounds: indene and indenone) are formed as a nearly equal mixture of regioisomers. The proportion of indene and phenol products is dependent on the concentration with greater amounts of phenol products being formed at higher concentrations. The total regioselectivity of all of the products is also a function of the concentration. This result could be due either to an equilibration of the η1,η3-Vinyl Carbene intermediates in this reaction or to a change in mechanisms in the formation of the η1,η3-Vinyl Carbene intermediates from one involving a dissociative incorporation of the alkyne to one involving an associative incorporation of the alkyne. Kinetic studies reveal that ...
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Stereoelectronic effects on product formation from the E- And Z-isomers of η1,η3-Vinyl Carbene complexed intermediates in the reactions of Fischer Carbene complexes with alkynes
Organometallics, 1998Co-Authors: Marcey L. Waters, William D. Wulff, Timothy A. Brandvold, Lyle D. Isaacs, Arnold L. RheingoldAbstract:The reactions of 2-dihydropyranyl(methoxy)methylene pentacarbonyl chromium 19 with the series of five acetylenic ketones CH3(CH2)2C⋮C(O)(p-X−C6H4) 26 (X = CF3, Cl, H, OCH3, NMe2) gave a mixture of phenol and lactone products. The most electron-rich alkyne (X = NMe2) gave a greater proportion of the phenol product 27 (81:19), and the most electron-poor alkyne (R = CF3) gave the lactone 28 as the major product (64:36). Since the lactone product must come from a Z-isomer of a Vinyl Carbene complexed intermediate and the phenol product must come an E-isomer, this reveals that the stereochemistry of the reactive intermediates involved can be influenced by electronic effects of the substituents on the alkyne. A similar set of experiments with 3-hexyn-2-one 20 and the series of five phenoxy Carbene complexes (CO)5CrC(C5H6O)O(p-X−C6H4) 29 (X = CF3, Cl, H, OCH3, NMe2) produced the opposite result, where predominantly the phenol product was produced from the most electron-poor Carbene complex (X = CF3) and for the ...
Min Shi - One of the best experts on this subject based on the ideXlab platform.
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rhodium ii catalyzed and thermally induced intramolecular migration of n sulfonyl 1 2 3 triazoles new approaches to 1 2 dihydroisoquinolines and 1 indanones
Chemistry: A European Journal, 2016Co-Authors: Run Sun, Yu Jiang, Xiangying Tang, Min ShiAbstract:New rhodium(II)-catalyzed or thermally induced intramolecular alkoxy group migration of N-sulfonyl-1,2,3-triazoles has been developed, affording divergent synthesis of 1,2-dihydroisoquinoline and 1-indanone derivatives according to different conditions. N-Sulfonyl keteneimine is the key intermediate for the synthesis of dihydroisoquinoline, whereas the aza-Vinyl Carbene intermediate results in the formation of 1-indanone.
Damián Padín - One of the best experts on this subject based on the ideXlab platform.
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Cp*RuCl‐Vinyl Carbenes: Two Faces and the Bifunctional Role in Catalytic Processes
Chemistry (Weinheim an der Bergstrasse Germany), 2020Co-Authors: Damián Padín, Jesús A. Varela, Carlos SaáAbstract:Ruthenium Vinyl Carbenes derived from Cp/Cp*RuCl-based complexes (Cp=cyclopentadiene, Cp*=1,2,3,4,5-pentamethylcyclopentadiene) have been routinely invoked as key intermediates in tandem reactions involving a Carbene/alkyne metathesis (CAM). A priori, these intermediates resemble the Grubbs-type family of catalysts, but they exhibit a completely different reactivity pattern that few, if any, other catalytic system can reproduce so far. The reactivity of these species with α-unsubstituted and α-substituted alkynals showcases the peculiarities of these intermediates. Although Z-Vinyl dihydrooxazines are preferentially obtained with the former, Z-Vinyl epoxypyrrolidines are obtained with the latter. A combination of spectroscopic and computational data now prove that a η3 -coordination mode of the ruthenium Vinyl Carbene and the presence of a Lewis basic chloride ligand give rise to two markedly different stereoelectronic faces, which are responsible for the unconventional reactivity of these species.
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Recent Advances in Ruthenium-Catalyzed Carbene/Alkyne Metathesis (CAM) Transformations
Synlett, 2020Co-Authors: Damián Padín, Jesús A. Varela, Carlos SaáAbstract:Carbene intermediates have shown versatile applications in modern synthetic chemistry. Catalytic ruthenium Carbene/alkyne metathesis (CAM) with readily available substrates renders an efficient procedure for the in situ generation of ruthenium Vinyl Carbene intermediates. Here, recent advances in synthetic applications of ruthenium-catalyzed Carbene/alkyne metathesis (CAM) are highlighted. 1 Introduction 2 Ruthenium Vinyl Carbenes through Carbene/Alkyne Metathesis (CAM) 3 Nonpolar Transformations of Ruthenium Vinyl Carbenes 4 Polar Transformations of Ruthenium Vinyl Carbenes 4.1 Intramolecular Ruthenium-Catalyzed [1,5]- and [1,6]-Hydride Transfer/Cyclization 4.2 Heterocyclizations of Alkynals and Alkynones 4.3 Heterocyclizations of ortho-(Alkynyloxy)benzylamines 5 DFT Studies on the Stereoselectivity of the CAM Reaction 6 Conclusions
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[2 + 1] Cycloaddition of Catalytic Ruthenium Vinyl Carbenes: A Stereoselective Controlled Access to (Z)- and (E)-Vinyl Epoxypyrrolidines
ACS Catalysis, 2016Co-Authors: Damián Padín, Fermín Cambeiro, Martin Fananas‐mastral, Jesús A. Varela, Carlos SaáAbstract:Aza-alkynals undergo a cyclization reaction with diazo compounds in the presence of catalytic amounts of Cp*RuCl(cod) to afford Vinyl epoxypyrrolidines, valuable building blocks for the synthesis of biologically active molecules. Ruthenium Vinyl Carbene intermediates have been invoked to explain the overall [2 + 1] cycloaddition (epoxy-annulation reaction). The reaction proceeds under mild conditions and in short reaction times (5–80 min) with complete (Z)- or (E)-stereoselectivity on the Vinyl substituent, depending on the nature of the diazo compound used. Theoretical calculations support a mechanistic rationale to explain this controlled process.
Takeshi Takeda - One of the best experts on this subject based on the ideXlab platform.
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Titanacyclobutenes or Titanium Vinyl Carbene Complexes? Reactivity of Organotitanium Species Generated by the Reaction of γ‐Chloroallyl Sulfides with a Titanocene(II) Reagent
Chemistry (Weinheim an der Bergstrasse Germany), 2007Co-Authors: Tomohiro Shono, Rie Kurashige, Ryo Mukaiyama, Akira Tsubouchi, Takeshi TakedaAbstract:The reactivity of the organotitanium species generated by the reductive titanation of gamma-chloroallyl sulfides with the titanocene(II) reagent [Cp(2)Ti{P(OEt)(3)}(2)] was studied. The organotitanium species formed from alpha-monosubstituted gamma-chloroallyl sulfides reacted with 1,5-diphenylpentan-3-one and styrene to produce conjugated dienes and Vinyl cyclopropanes as major products, thus suggesting the formation of Vinyl Carbene complexes as intermediates. On the contrary, the organotitanium species generated from acyclic beta,gamma-disubstituted gamma-chloroallyl sulfides revealed titanacyclobutene-like reactivity, and their reaction with 1,5-diphenylpentan-3-one produced homoallyl alcohols. These organotitanium species did not react with styrene, but did react with dichlorophenylphosphine to afford phosphacyclobutenes. In the case of beta-monosubstituted, gamma-monosubstituted, and alpha,gamma-disubstituted gamma-chloroallyl sulfides, the organotitanium species reacted with both 1,5-diphenylpentan-3-one and styrene. The former reaction produced homoallyl alcohols and the latter gave Vinyl cyclopropanes or unconjugated dienes. These results suggest that titanacyclobutenes and/or titanium Vinyl Carbene complexes are produced by the reductive titanation of gamma-chloroallyl sulfides depending on their substitution patterns.
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titanacyclobutenes or titanium Vinyl Carbene complexes reactivity of organotitanium species generated by the reaction of γ chloroallyl sulfides with a titanocene ii reagent
Chemistry: A European Journal, 2007Co-Authors: Tomohiro Shono, Rie Kurashige, Ryo Mukaiyama, Akira Tsubouchi, Takeshi TakedaAbstract:The reactivity of the organotitanium species generated by the reductive titanation of gamma-chloroallyl sulfides with the titanocene(II) reagent [Cp(2)Ti{P(OEt)(3)}(2)] was studied. The organotitanium species formed from alpha-monosubstituted gamma-chloroallyl sulfides reacted with 1,5-diphenylpentan-3-one and styrene to produce conjugated dienes and Vinyl cyclopropanes as major products, thus suggesting the formation of Vinyl Carbene complexes as intermediates. On the contrary, the organotitanium species generated from acyclic beta,gamma-disubstituted gamma-chloroallyl sulfides revealed titanacyclobutene-like reactivity, and their reaction with 1,5-diphenylpentan-3-one produced homoallyl alcohols. These organotitanium species did not react with styrene, but did react with dichlorophenylphosphine to afford phosphacyclobutenes. In the case of beta-monosubstituted, gamma-monosubstituted, and alpha,gamma-disubstituted gamma-chloroallyl sulfides, the organotitanium species reacted with both 1,5-diphenylpentan-3-one and styrene. The former reaction produced homoallyl alcohols and the latter gave Vinyl cyclopropanes or unconjugated dienes. These results suggest that titanacyclobutenes and/or titanium Vinyl Carbene complexes are produced by the reductive titanation of gamma-chloroallyl sulfides depending on their substitution patterns.