Zinc‐Catalyzed Synthesis of Functionalized Furans and Triarylmethanes from Enynones and Alcohols or Azoles: Dual XH Bond Activation by Zinc

González, Jesús; González, Javier; Pérez-Calleja, Carmela; López, Luís A.; Vicente, Rubén

doi:10.1002/anie.201301625

Cited by 131 publications

(44 citation statements)

References 57 publications

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“…Particularly, the zinc-catalyzed reaction of enynones with various azoles efficiently led to the formation of unsymmetrically substituted triarylmethane derivatives (Scheme 34). 53 Similar to the reaction with alcohols, activation of N-H bond by zinc was proposed to be responsible for the outcome of this transformation.…”

Section: Scheme 33mentioning

confidence: 98%

“…Interestingly, the reaction of enynone with alcohols in the presence of ZnCl 2 led to the formation of ether derivatives, resulting from a formal insertion into the O-H bond of the alcohol. 53 This protocol could be applied to various enynones and primary alcohols, while higher loadings of ZnCl 2 were required in the case of secondary alcohols. Remarkably, the reactions with allylic alcohol (138) (Scheme 32) or propargylic alcohol took place with complete chemoselectivity affording the corresponding ethers in good yields.…”

Section: Zinc-catalyzed Reaction Of Enynones and Alcohols Or Azoles Imentioning

confidence: 99%

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Zinc reagents as non-noble catalysts for alkyne activation

González¹,

López²,

Vicente³

2015

Tetrahedron Letters

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Section: Scheme 33mentioning

confidence: 98%

Section: Zinc-catalyzed Reaction Of Enynones and Alcohols Or Azoles Imentioning

confidence: 99%

Zinc reagents as non-noble catalysts for alkyne activation

González¹,

López²,

Vicente³

2015

Tetrahedron Letters

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“…Zuschriften explained, however,b ya ssuming that the p-acidic metal fragment activates the substrate to the extent that attack of the ketone onto the triple bond is faster than binding of H 2 ,as necessary for gem-hydrogenation to occur. This type of mechanism has ample precedent in the literature for many different carbophilic catalysts, [19] although rigorous proof for the intervention of discrete carbenes is exceedingly rare. [20] To test this hypothesis,e nyne 15 was reacted with stoichiometric amounts of [Cp*RuCl] 4 in the presence as well as in the absence of H 2 :e ither set-up afforded the very same pianostool ruthenium carbene 20 in less than 30 min reaction time.The structure of this remarkable complex in the solid state shows that the ruthenium atom no longer interacts with the adjacent -OMe group (Figure 2);r ather,i ti st ightly ligated to the electron rich "enol ether" site of the newly formed furan ring as manifested in the observed distances as well as in an elongated C2ÀC3 bond.…”

Section: Angewandte Chemiementioning

confidence: 99%

Mechanistic Divergence in the Hydrogenative Synthesis of Furans and Butenolides: Ruthenium Carbenes Formed by gem‐Hydrogenation or through Carbophilic Activation of Alkynes

Peil

Fürstner

2019

Angewandte Chemie

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Enynes with at ethered carbonyl substituent are converted into substituted furan derivatives upon hydrogenation using [Cp*RuCl] 4 as the catalyst. Paradoxically,t his transformation can occur along two distinct pathways,each of which proceeds via discrete pianostool ruthenium carbenes.In the first case,h ydrogenation and carbene formation are synchronized ("gem-hydrogenation"), whereas the second pathway comprises carbene formation by carbophilic activation of the triple bond, followed by hydrogenative catalyst recycling.Representative carbene intermediates of either route were characterized by X-ray crystallography;t he structural data prove that the attacko ft he carbonyl group on the electrophilic carbene center follows aBürgi-Dunitz trajectory.After ac entury of intense research by the scientific community on catalytic hydrogenation, our group has recently been able to identify an entirely new reactivity mode.S pecifically,i tw as shown that alkynes can undergo gem-hydrogenation, ar eaction in which both H-atoms of H 2 are delivered to one and the same acetylenic C-atom while the adjacent position is concomitantly transformed into adiscrete metal carbene. [1,2] At the current stage of development, [Cp*RuCl] 4 is the precatalyst of choice;m oreover,h eteroatom substituents in vicinity of the triple bond are often necessary to render the reaction efficient. Detailed spectroscopic and computational data indicate that the resulting pianostool ruthenium complexes basically exhibit aF ischercarbene character with ac ertain overtone reminiscent of Grubbs-type catalysts. [3] This view is corroborated by the fact that they participate in either intramolecular cyclopropanation or metathesis reactions,d epending on the chosen substrate. [4] Fort heir largely electrophilic nature,s uch complexes should be able to participate in various other catalytic transformations too.I ft his is the case, gem-hydrogenation might eventually evolve into an attractive alternative to diazoalkane decomposition, which is arguably the most common gateway to highly reactive late-transition metal carbenes. [5,6] Thef oray along these lines outlined below was inspired by ar ecent publication describing an innovative entry into highly substituted furan derivatives (Scheme 1). [7] Specifically,d iazo compounds A were shown to react with catalytic [CpRu(MeCN) 3 ]PF 6 to generate transient cationic ruthenium carbenes B,w hich get trapped by the tethered ester group to give the corresponding heterocycle C.W e reasoned that this type of transformation might be emulated by gem-hydrogenation of enyne D,i nw hich the propargylic -OR substituent directs carbene formation to the distal acetylenic site. [1,2] Akin to B,t he resulting intermediate E might furnish furan F,even though E is aneutral rather than cationic entity.In line with our expectations,p roduct 2 was formed in almost quantitative yield (! 95 %) upon stirring of asolution of 1 and [Cp*RuCl] 4 (2 mol %) in CH 2 Cl 2 under an atmosphere of H 2 (1 bar) for 3h at ambient temperature (Scheme ...

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“…Metal carbenes, in many cases converted from vinyl metal species, are often proposed as key intermediate in these transformations910. In the past 15 years, the transition-metal-catalysed cycloisomerization of ene–yne–ketones has been well established, and provides a safe, effective and practical alternative to the diazo decomposition route for metal carbene generation11121314151617181920212223. In the transformations, the metal π-activated alkyne is attacked by the carbonyl oxygen through 5- exo -dig cyclization to generate zwitterionic vinyl metal intermediate A that could be transformed into its resonance structure, metal (2-furyl)carbene intermediate B (Fig.…”

mentioning

confidence: 99%

“…In the transformations, the metal π-activated alkyne is attacked by the carbonyl oxygen through 5- exo -dig cyclization to generate zwitterionic vinyl metal intermediate A that could be transformed into its resonance structure, metal (2-furyl)carbene intermediate B (Fig. 1b, M=Cu1922, Au1823, Rh1315, Zn1718 and Pd2021). Metal carbene B subsequently undergoes a variety of transformations, such as oxidation, C-H insertion, cyclopropanation and heteroatom (N, O, Si, S)-H insertion reaction11121314151617181920212223.…”

mentioning

confidence: 99%

Synthesis and structures of gold and copper carbene intermediates in catalytic amination of alkynes

Wang

Cao

et al. 2017

Nat Commun

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Metal carbenes are often proposed as reactive intermediates in the late transition metal-catalysed transformations of alkynes. Owing to their high reactivity, however, isolation and structural characterization of metal carbene intermediates in these transformations has remained unknown. Herein, we report the isolation of two acyclic gold and copper carbene intermediates in either Au(I)- or Cu(I)-catalysed cyclization of N-alkynyl formamidines through five-exo-dig cyclization. X-ray diffraction, 13C NMR spectra data and computational analyses provide evidence for the formation of a gold carbene intermediate with a carbocation-like electronic character. Using the intrinsic bond orbital (IBO) approach, we also evaluate the π-stabilizing effects of organic substituents at the carbene carbon atom in the gold carbene intermediate. Another rare six-membered copper carbene complex is also obtained through 6-endo-dig cyclization. These metal carbenes have proven reactive toward oxidation. The metal-promoted cyclization of N-alkynyl formamidine provides a facile approach to synthesize metal carbene species.

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Zinc‐Catalyzed Synthesis of Functionalized Furans and Triarylmethanes from Enynones and Alcohols or Azoles: Dual XH Bond Activation by Zinc

Cited by 131 publications

References 57 publications

Zinc reagents as non-noble catalysts for alkyne activation

Zinc reagents as non-noble catalysts for alkyne activation

Mechanistic Divergence in the Hydrogenative Synthesis of Furans and Butenolides: Ruthenium Carbenes Formed by gem‐Hydrogenation or through Carbophilic Activation of Alkynes

Synthesis and structures of gold and copper carbene intermediates in catalytic amination of alkynes

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