Synthesis of Naturally Occurring Acetylenes via an Alkylidene Carbenoid Rearrangement

Shun, Annabelle L. K. Shi; Tykwinski, Rik R.

doi:10.1021/jo034734g

Cited by 45 publications

(22 citation statements)

References 22 publications

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“…In cases in which the pendant functionality was an aryl group (45a-c), the resulting ketones were surprisingly unstable and were converted directly into dibromoolefins (46a-c). Ketones with alkenyl substitution (45d-g) showed greater stability and could be isolated pure and fully characterized prior to elaboration to 46d-g. Rearrangement of 46a-g in hexanes gave conjugated triynes 47a-g under standard conditions [34][35]. …”

Section: Triynes From Acid Chloridesmentioning

confidence: 99%

“…Bohlmann's initial synthesis of 57 relied on the derivatization of a highly reactive triynal precursor [48]. A reported alternative synthesis of compound 57 involves only three steps from acid chloride 58, which is generated quantitatively from the commercially available carboxylic acid [35]. A typical sequence of Friedel-Crafts acylation (59) and dibromoolefination provides the necessary precursor 60, and the final FBW rearrangement with 60 proceeds nicely to give enetriyne 57 in 84 % yield.…”

Section: Natural Products Synthesismentioning

confidence: 99%

“…The initial step was a one-pot reaction consisting of the elimination of dibromoolefin 62 to provide acetylide 63 [52] and condensation with aldehyde 64 to give alcohol 65 in 54 % yield. With 65 to hand, a standard sequence of oxidation (66), dibromoolefination (67), and FBW rearrangement ultimately provided diyne 61 in 72 % yield, a 13 % yield overall from commercially available 64 [35].…”

Section: Natural Products Synthesismentioning

confidence: 99%

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Polyynes Via Alkylidene Carbenes and Carbenoids

Eisler

Tykwinski

2004

Acetylene Chemistry

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of detail it also surveys some of the unique properties displayed by these newly obtained materials, including solid-state structure and stability, and the linear and nonlinear optical properties of conjugated polyynes. Alkylidene Carbene and Carbenoid SpeciesAlkylidene carbenes/carbenoids (1 and 2) are reactive intermediates capable of undergoing several distinct reactions (Scheme 7.1) [13]. Carbenoid 1 and alkylidene carbene 2 are distinguished by the association of the carbon in 1 with a metal and a halogen (or another leaving group), while the free carbene 2 has no such ties. The two extremes can vary greatly in reactivity. Within this range of reactivity, solvent, b-substituent, and temperature can all affect the reaction outcome. For carbenoid intermediates, both the metal and the leaving group can also greatly influence the reaction [13e]. 261 7.3 Alkyne Formation from Carbenes and Carbenoids R R' 17 70% 16a X = ZnX 16b X = Li -20 ˚C to rt Et 2 O Equation 7-1 263 7.3 Alkyne Formation from Carbenes and Carbenoids H Cl BuLi, THF -90 ˚C 18 19 77% Equation 7-2 CH 3 H Cl CH 3 BuLi THF/Et 2 O > -70 ˚C 20 21 65% Equation 7-3 H Br Br Br t-BuOK ∆ 23 24 22 -40 ˚C to 0 ˚C PhLi, benzene/ether Equation 7-4 265 7.3 Alkyne Formation from Carbenes and Carbenoids Cl Cl Cl S Cl S S S S S S S BuLi, THF -90 to 0 ˚C 31 32 30% Equation 7-6 a Dibromoolefin formation as in Scheme 7.5.

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Section: Triynes From Acid Chloridesmentioning

confidence: 99%

Section: Natural Products Synthesismentioning

confidence: 99%

Section: Natural Products Synthesismentioning

confidence: 99%

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Polyynes Via Alkylidene Carbenes and Carbenoids

Eisler

Tykwinski

2004

Acetylene Chemistry

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“…[36] Advancing the scope of the FBWr required dibromoolefins as precursors, and these are readily available through a number of routes using standard transformations. [30,33] In the couple of years following our initial discovery, general approaches using the FBWr were developed to give (Table 1), for example, di-, tri-, and tetraynes (master's student Annabelle Shi Shun and undergraduate Erin Chernick), [33,37] natural product analogues, [35,38,39] polyyne sugars (in collaboration with my colleague in Alberta, Todd Lowary, and graduate students Thanh Luu and Wei Shi), [34] and a "one-pot" protocol to functionalized polyynes (developed by Yasuhiro Morisaki, a postdoc visiting from Professor Chujo's group in Kyoto). [38,40] It turns out that our "discovery" came just in time.…”

Section: Introductionmentioning

confidence: 99%

Carbyne: The Molecular Approach

Tykwinski

2015

The Chemical Record

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For the last 60+ years, the synthesis and study of cumulenes and polyynes have been the focus of a small, but dedicated, group of researchers. Many of the remarkable electronic, optical, and structural properties of cumulenes and polyynes had already been identified in the earliest reports. The molecular lengths achievable by the initial syntheses were, unfortunately, somewhat limited by synthetic methods available. For the past 15 years, we have worked toward expanding on the synthesis of cumulenes and polyynes through the development of new methods and stabilization motifs. As new compounds have become available, homologous series of cumulenes and polyynes have then been examined as a function of molecular length. While we are not yet there, we would like to eventually provide a general description of the sp-carbon allotrope carbyne, and this account presents some of our efforts toward this goal.

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“…Desilylation of acetylenic compounds can be performed with the use of various reagents, among which such bases as alkali metal hydroxides [6], alkoxides [7], and carbonates [8] in protophylic solvents, as well as potassium [9] and ammonium fluorides [10] are used most frequently. We recently showed that successful desilylation may be achieved with the aid of even weak bases generated in protic medium from metal oxides (PbO 2 , MnO 2 , Co 2 O 3 , Ni 2 O 3 ) [11].…”

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confidence: 99%

Highly efficient desilylation of 3-trimethylsilylprop-2-ynamides by the action of KF-Al2O3

2011

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A highly effective procedure has been developed for desilylation of 3-trimethylsilylprop-2-ynamides in the presence of KF-Al 2 O 3 as catalyst. The corresponding terminal prop-2-ynamides were obtained in high yield in methanol at 25°C using 5 mol % of the catalyst (reaction time 20 min). Rise in temperature leads to the formation of Z,E-3-methoxyprop-2-enamides or 3,3-dimethoxypropanamides as a result of tandem desilylation-addition of methanol, depending on the conditions. The synthetic strategy silylation-desilylation of triple bond is widely used in fine organic synthesis, in particular in total syntheses of highly efficient natural antibiotics [1]. This approach was partially reviewed in [2]. The presence of a trimethylsilyl group at triple C≡C bond stabilizes the latter so that it becomes inactive toward nucleophiles [3], organometallic compounds, and transition metal catalysts in various synthetic transformations [4]; as a result, regioselective cycloaddition of azides at the triple bond of various trimethylsilylalkynes becomes possible [5], the stability of compounds increases, and their solubility in organic solvents is improved.Desilylation of acetylenic compounds can be performed with the use of various reagents, among which such bases as alkali metal hydroxides [6], alkoxides [7], and carbonates [8] in protophylic solvents, as well as potassium [9] and ammonium fluorides [10] are used most frequently. We recently showed that successful desilylation may be achieved with the aid of even weak bases generated in protic medium from metal oxides (PbO 2 , MnO 2 , Co 2 O 3 , Ni 2 O 3 ) [11].Despite diversity of desilylating agents, published data on desilylation of silicon-containing acetylenic compounds with an activated triple bond are few in number. Desilylation of such compounds requires mild conditions, taking into account the possibility for undesirable addition of alcohol or water (used as solvent) at the terminal triple bond in the resulting alkynes by the action of base in protophilic medium.In the present work we developed an efficient procedure for desilylation of trimethylsilylacetylenes having an activated triple bond. 3-Trimethylsilylprop-2-ynamides Ia-Ig were selected as substrates, and KFAl 2 O 3 , as reagent. Solid-phase desilylation of trimethylsilylalkynes under microwave irradiation required excess KF-Al 2 O 3 (4 equiv) [12]. There are no published data on desilylation of trimethylsilylacetylene derivatives with an activated triple bond by the action of KF-Al 2 O 3 . O Ia-Ig KF-Al 2 O 3 (5 mol %) MeOH, 25°C, 20 min HC NR 1 R 2 O IIa-IIg R 1 = H, R 2 = H (a), Ph (b), PhCH 2 (c), 2,5-Cl 2 C 6 H 3 (d), 3-BrC 6 H 4 (e), HOCH 2 CMe 2 (f); R 1 R 2 N = morpholino (g).

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Synthesis of Naturally Occurring Acetylenes via an Alkylidene Carbenoid Rearrangement

Cited by 45 publications

References 22 publications

Polyynes Via Alkylidene Carbenes and Carbenoids

Polyynes Via Alkylidene Carbenes and Carbenoids

Carbyne: The Molecular Approach

Highly efficient desilylation of 3-trimethylsilylprop-2-ynamides by the action of KF-Al2O3

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