Mechanistic Aspects of Alkyne Migration in Alkylidene Carbenoid Rearrangements

Bichler, Paul; Chalifoux, Wesley A.; Eisler, Sara; Shun, Annabelle L. K. Shi; Chernick, Erin T.; Tykwinski, Rik R.

doi:10.1021/ol8023665

Cited by 32 publications

(24 citation statements)

References 48 publications

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“…Figure shows an excerpt from the resulting 13 C NMR spectrum; the singlets at the positions marked C1, C2, C3 and C4 are assigned to unlabeled 4 b , while the two doublets for the labeled positions C2 and C3 in 4 b* (see above) come along with two doublets of doublets for the unlabeled carbon atoms C1 and C4, which display 1 J CC / 2 J CC couplings of 147/18 Hz and 196/25 Hz, respectively. It should be noted that the DYCM protocol provides convenient access to symmetrical and unsymmetrical doubly 13 C‐labeled 1,3‐butadiynes which are difficult to be obtained by other methods …”

Section: Resultsmentioning

confidence: 99%

Unraveling the Mechanism of 1,3‐Diyne Cross‐Metathesis Catalyzed by Silanolate‐Supported Tungsten Alkylidyne Complexes

Schnabel

Melcher

Brandhorst

et al. 2018

Chemistry A European J

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The benzylidyne complex [PhC≡W{OSi(OtBu) } ] (1) catalyzed the cross-metathesis between 1,4-bis(trimethylsilyl)-1,3-butadiyne (2) and symmetrical 1,3-diynes (3) efficiently, which gave access to TMS-capped 1,3-diynes RC≡C-C≡CSiMe (4). Diyne cross-metathesis (DYCM) studies with C-labeled diyne PhC≡ C- C≡CPh (3*) revealed that this reaction proceeds through reversible carbon-carbon triple-bond cleavage and formation according to the conventional mechanism of alkyne metathesis. The reaction between 1 and 3* afforded the 3-phenylpropynylidyne complex PhC≡ C- C≡W{OSi(OtBu) } ] (5*), indicating that alkynylalkylidyne complexes are likely to act as catalytically active species. Attempts to isolate 5* from mixtures of 1 and 3* afforded crystals of the ditungsten 2-butyne-1,4-diylidyne complex [(tBuO) SiO} W≡ C- C≡ C- C≡W{OSi(OtBu) } ] (6*), which was additionally characterized by X-ray diffraction analysis. Depolymerization-macrocyclization of a carbazole-butadiyne polymer, obtained from 3,6-diethynyl-9-dodecylcarbazole (7) under copper-catalyzed Hay coupling conditions, was also efficiently catalyzed by 1 and afforded a mixture of mono-, diyne- and triyne-containing tetrameric macrocycles, revealing that diyne disproportionation into monoynes and triynes occurs as a slow side reaction that interferes with a high diyne metathesis selectivity. Potential catalytic pathways were studied by means of quantum-chemical calculations, and kinetic studies were performed to substantiate an α,α-mechanism for the catalytic diyne metathesis reaction, which involves intermediate alkynylalkylidyne and α,α'-dialkynylmetallacyclobutadiene intermediates.

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Section: Resultsmentioning

confidence: 99%

Unraveling the Mechanism of 1,3‐Diyne Cross‐Metathesis Catalyzed by Silanolate‐Supported Tungsten Alkylidyne Complexes

Schnabel

Melcher

Brandhorst

et al. 2018

Chemistry A European J

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“…47 This reaction was also the first example of an alkynyl group undergoing 1,2-migration. 47,48 This method has been widely used in the synthesis of polyynes. 49 Tani reported the formation of fused cyclopentene 64 by treating dihaloalkene 63 with excess SmI 2 and HMPA (Scheme 28).…”

Section: A-elimination Of Metal Carbenoidsmentioning

confidence: 99%

Recent advances in alkylidene carbene chemistry

Grainger

Munro

2015

Tetrahedron

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“…For the synthesis of [7]tBuPh (Scheme 3), a Fritsch-Buttenberg-Wiechell (FBW) rearrangement was used to form the requisite triyne framework of 5 a through the reaction of ketone 6 a [19] with Colvins reagent. [20] Subsequent reduction of 5 a gave [7]tBuPh. While attempts to directly isolate [7]tBuPh through precipitation resulted in decomposition, the pure cumulene could be isolated by slow crystallization from a solution of CH 2 Cl 2 /MeOH, and the crystalline solid was stable indefinitely in the absence of O 2 .…”

Section: Dedicated To Professor Franåois Diederich On the Occasion Ofmentioning

confidence: 99%

Synthesis and Structure of Tetraarylcumulenes: Characterization of Bond‐Length Alternation versus Molecule Length

et al. 2013

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Dedicated to Professor FranÅois Diederich on the occasion of his 60 th birthday Chains composed of sp-hybridized carbon atoms have been explored for decades because of their unique linear structure and interesting physical properties. [1] More recently, the wirelike nature of sp-carbon oligomers has inspired a variety of studies that aim to evaluate these structures as components in nanometer-sized devices. [2] Particularly interesting is the reported formation of such wires linking graphene nanoribbons, offering the prospect of all-carbon-based devices. [2d-f, 3] Molecules composed of a skeleton of sp-hybridized carbon atoms can be constructed from a framework of either polyynes (alternating single and triple bonds) or cumulenes (cumulated double bonds). The chemistry of polyynes has been advanced to systems as long as 44 consecutive carbon atoms (22 acetylene units), [4] and studies have shed considerable light on the physical and optoelectronic properties of polyynes. [5] However, the study of cumulenes has lain essentially dormant since early work [6,7] reported by Kuhn [8,9] and Bohlmann. [10,11] Thus, there remain many unanswered questions about the physical properties of this intriguing class of linear molecules. To date, UV/Vis spectroscopy has been the most useful method for the characterization of cumulenes, [12] and analyses of cumulenes show a lowering of the lowest-energy electronic absorption (l max ) as a function of length, such as that for [n]Ph and [n]Cy (n = 3, 5, 7, 9, Figure 1). [9][10][11] Obviously, changes in l max versus molecular length are intricately dependent on structure and on the degree of bond-length alternation (BLA, defined as the bondlength difference between the two central-most double bonds of the cumulene chain). Recent theoretical studies predict that the BLA for cumulenes will rapidly approach zero (BLA 0.01), [13][14][15] that is, Peierls distortion is essentially absent. [16] Experimentally, X-ray crystallographic analysis would provide an opportunity to confirm or refute theoretical trends in BLA as a function of cumulene length. Unfortunately, few solid-state structures have been reported for cumulenes, and data for [n]cumulenes with n > 5 are not available. The results presented herein offer an answer to the important question of BLA in long cumulenes.It was clear from the onset of the study that the synthesis and solid-state analysis of long [n]cumulenes (n > 5) would be challenging, because available reports emphasized that these species were not typically stable enough for isolation. [6] In order to stabilize the cumulene core through steric shielding, initial efforts targeted formation of the [n]tBuPh series of cumulenes ( Figure 1). It quickly became clear, however, that the di(tert-butyl)phenyl (R = tBu 2 C 6 H 3 ) groups do not afford a sufficient stabilizing force to easily isolate the [7]-and [9]tBuPh cumulenes, and our attention then switched to the [n]Mes series.Synthesis of [3]tBuPh began with the formation of 1 a through reaction of the Li-acetylide of...

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Mechanistic Aspects of Alkyne Migration in Alkylidene Carbenoid Rearrangements

Cited by 32 publications

References 48 publications

Unraveling the Mechanism of 1,3‐Diyne Cross‐Metathesis Catalyzed by Silanolate‐Supported Tungsten Alkylidyne Complexes

Unraveling the Mechanism of 1,3‐Diyne Cross‐Metathesis Catalyzed by Silanolate‐Supported Tungsten Alkylidyne Complexes

Recent advances in alkylidene carbene chemistry

Synthesis and Structure of Tetraarylcumulenes: Characterization of Bond‐Length Alternation versus Molecule Length

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