ChemInform Abstract: Gold‐Catalyzed Oxidative Cyclizations of cis‐3‐En‐1‐ynes To Form Cyclopentenone Derivatives.

Bhunia, Sabyasachi; Ghorpade, Satish; Huple, Deepak B.; Liu, Ru‐Shi

doi:10.1002/chin.201233103

Cited by 2 publications

(5 citation statements)

References 9 publications

(23 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…As a result, the venerable C–H insertions by Rh carbenes/carbenoids have not been realized with the gold counterpart. 22 In addition, its electrophilicity is evident in the observed chloride abstraction from the reaction solvent, 1,2-dichloroethane, under acidic conditions (eq 3). In comparison, similar chloride abstractions were observed with Rh carbenes/carbenoids flanked by two electron-withdrawing acyl groups.…”

Section: Intermolecular Oxidation Of Terminal Alkynes Followed By Intmentioning

confidence: 99%

“…While other research groups have shown the α-oxo gold carbene generated via the intermolecular oxidation strategy could undergo cyclopropanation with tethered alkenes in special cases, , the carbene center appears to be highly electrophilic and behaves mostly as a carbocation. As a result, the venerable C–H insertions by Rh carbenes/carbenoids have not been realized with the gold counterpart . In addition, its electrophilicity is evident in the observed chloride abstraction from the reaction solvent, 1,2-dichloroethane, under acidic conditions (eq ).…”

Section: Intermolecular Oxidation Of Terminal Alkynes Followed By Int...mentioning

confidence: 99%

“…In this Account, I will discuss our results based both on intramolecular alkyne oxidation and on intermolecular oxidation, with the latter being the focus. I am, however, obligated to point out here that many other researchers including Liu, 17−22 Toste, 23 Shin, 24,25 Zhang, 26−28 Davies, 29−31 Gagosz, 32 Hashmi, 33,34 Li, 35 and Liu 36 have also made outstanding contributions in this field, which will not be discussed due to the nature of this Account.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

A Non-Diazo Approach to α-Oxo Gold Carbenes via Gold-Catalyzed Alkyne Oxidation

2014

View full text Add to dashboard Cite

For the past dozen years, homogeneous gold catalysis has evolved from a little known topic in organic synthesis to a fully blown research field of significant importance to synthetic practitioners, due to its novel reactivities and reaction modes. Cationic gold(I) complexes are powerful soft Lewis acids that can activate alkynes and allenes toward efficient attack by nucleophiles, leading to the generation of alkenyl gold intermediates. Some of the most versatile aspects of gold catalysis involve the generation of gold carbene intermediates, which occurs through the approach of an electrophile to the distal end of the alkenyl gold moiety, and their diverse transformations thereafter. On the other hand, α-oxo metal carbene/carbenoids are highly versatile intermediates in organic synthesis and can undergo various synthetically challenging yet highly valuable transformations such as C–H insertion, ylide formation, and cyclopropanation reactions. Metal-catalyzed dediazotizations of diazo carbonyl compounds are the principle and most reliable strategy to access them. Unfortunately, the substrates contain a highly energetic diazo moiety and are potentially explosive. Moreover, chemists need to use energetic reagents to prepare them, putting further constrains on operational safety.In this Account, we show that the unique access to the gold carbene species in homogeneous gold catalysis offers an opportunity to generate α-oxo gold carbenes if both nucleophile and electrophile are oxygen. Hence, this approach would enable readily available and safer alkynes to replace hazardous α-diazo carbonyl compounds as precursors in the realm of gold carbene chemistry.For the past several years, we have demonstrated that alkynes can indeed effectively serve as precursors to versatile α-oxo gold carbenes. In our initial study, we showed that a tethered sulfoxide can be a suitable oxidant, which in some cases leads to the formation of α-oxo gold carbene intermediates. The intermolecular approach offers excellent synthetic flexibility because no tethering of the oxidant is required, and its reduced form is not tangled with the product. We were the first research group to develop this strategy, through the use of pyridine/quinolone N-oxides as the external oxidants. In this manner, we can effectively make a C–C triple bond a surrogate of an α-diazo carbonyl moiety in various gold catalyses. With terminal alkynes, we demonstrated that we can efficiently trap exclusively formed terminal carbene centers by internal nucleophiles en route to the formation of cyclic products, including strained oxetan-3-ones and azetidin-3-ones, and by external nucleophiles when a P,N-bidentate ligand is coordinated to gold. With internal alkynes, we generated synthetically useful regioselectivities in the generation of the α-oxo gold carbene moiety, which enables expedient formation of versatile enone products. Other research groups have also applied this strategy en route to versatile synthetic methods. The α-oxo gold carbenes appear to be more electrophilic...

show abstract

Section: Intermolecular Oxidation Of Terminal Alkynes Followed By Intmentioning

confidence: 99%

Section: Intermolecular Oxidation Of Terminal Alkynes Followed By Int...mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

A Non-Diazo Approach to α-Oxo Gold Carbenes via Gold-Catalyzed Alkyne Oxidation

2014

View full text Add to dashboard Cite

show abstract

“…27 Unlike nitrones, these pyridine-N-oxides are reluctant to undergo [3 þ 2] dipolar cycloadditions with alkynes and can participate as outer-sphere oxidants on a Au-coordinated alkyne. This external oxygenation strategy was widely successful in OÀH/NÀH insertion, 28 1,2-H shift for the synthesis of R,β-unsaturated carbonyls, 29 CÀH insertion, 30 cyclopropanation, 31 and halide abstraction from solvents. 32 7.…”

Section: Intermolecular Alkyne Oxygenationmentioning

confidence: 99%

“…Experimental evidence supporting the involvement of α-oxo gold carbenes is still lacking, and their involvement has been refuted in a number of studies. , It is likely that the key N–O cleavage step may be concerted with a 1,2-H (or alkyl) shift (Schemes and A) or a S N 2′ attack . In addition, a [3,3]-sigmatropic shift , is possible in many cases (Scheme B), and the antarafacial [1,3]-sigmatropic shift for N–O cleavage has not been completely ruled out …”

Section: Involvement Of the Gold Carbenes In The Cleavage Of N–o Bond?mentioning

confidence: 99%

Catalytic Access to α-Oxo Gold Carbenes by N–O Bond Oxidants

2014

View full text Add to dashboard Cite

Metal carbenes are highly versatile species that mediate various transformations. Recent advances in gold catalysis have allowed catalytic access to α-oxo metal carbenes from the alkyne functionality. Compared with traditional methods that rely upon metal-catalyzed decomposition of diazo precursors, the generation of this synthon occurs in an environmentally more appealing fashion by gold-catalyzed alkyne oxygenation. Hydroxylamine derivatives are typically prepared from hydroxylamine salts that are cheap and can be handled without special precaution. In reactions with an alkyne activated by gold, relatively stable nitrones and related reagents undergo efficient O-atom transfer to form putative α-oxo gold carbenes. The highly reactive nature of these species could be utilized in a variety of cascade transformations. Herein, recent synthetic methods based on this reactivity as well as the currently available mechanistic and structural studies through computational and experimental methods have been discussed. A variety of tandem reactions performed by our laboratory and others have demonstrated the synthetic utility of catalytically generated α-oxo gold carbenes and enabled access to various heterocycles. For example, a reaction between nitrones and alkynes led to azomethine ylides for the [3 + 2] dipolar cycloaddition. Alternatively, α-oxo gold carbenes can be transformed into enolate equivalents through a 1,2-pinacol shift. The addition of hydroxylamine derivatives across triple bonds led to oxoamination, providing α-aminocarbonyl compounds or regioselective Fisher indole-type synthesis. N-O bond cleaving redox chemistry paved the way for intermolecular redox processes, most notably by use of pyridine-N-oxide derivatives with expanding synthetic applications. In closing, other metal-based oxygenations using N-O bond oxidants will be highlighted. One particularly interesting aspect is the process leading to metal vinylidene complexes. Trapping of this intermediate resulted in opposite regioselectivity from gold catalysis in alkyne oxygenation and led to ketene intermediates for use in subsequent cascade transformations.

show abstract

ChemInform Abstract: Gold‐Catalyzed Oxidative Cyclizations of cis‐3‐En‐1‐ynes To Form Cyclopentenone Derivatives.

Abstract: Scheme 3. Deuterium-labeling experiments.Scheme 4. The reaction using diazocarbonyl.Scheme 5. The nature of CÀH insertion.Scheme 6. A plausible reaction mechanism.

Cited by 2 publications

References 9 publications

A Non-Diazo Approach to α-Oxo Gold Carbenes via Gold-Catalyzed Alkyne Oxidation

A Non-Diazo Approach to α-Oxo Gold Carbenes via Gold-Catalyzed Alkyne Oxidation

Catalytic Access to α-Oxo Gold Carbenes by N–O Bond Oxidants

Contact Info

Product

Resources

About