Type I intramolecular cycloadditions of vinylketenes

Lee, Susanna Y.; Kulkarni, Yashwant S.; Burbaum, Beverly W.; Johnston, Madeline I.; Snider, Barry B.

doi:10.1021/jo00244a002

Cited by 39 publications

(16 citation statements)

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“…Two-dimensional NMR spectroscopy indicated that the major diastereomer formed in all cases possesses the 2,3- syn , 2,5- syn stereochemistry (cf. 34a ), in accord with literature precedent for similar ketene–olefin cycloadditions. − It is likely that a substrate conformer in which the C5 group adopts a pseudoequatorial orientation in the transition state for [2 + 2] cycloaddition gives rise to the observed stereochemistry.…”

Section: Thermal Retro-ene/[2 + 2] Cycloaddition Reactions Of Tert-bu...supporting

confidence: 82%

“…Ketene intermediates are commonplace in the sigmatropic rearrangement chemistry of allyl and benzyl alkynyl ethers. It has been shown that ketenes also undergo a facile [2 + 2] cycloaddition with alkenes to form cyclobutanones, and the intramolecular variant of this process has been studied extensively by the groups of Marko, Snider, and Brady . However, the ketene intermediates utilized for these [2 + 2] cycloaddition reactions are most frequently generated from the corresponding acid chlorides by treatment with tertiary amines.…”

Section: Thermal Retro-ene/[2 + 2] Cycloaddition Reactions Of Tert-bu...mentioning

confidence: 99%

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Tandem Bond-Forming Reactions of 1-Alkynyl Ethers

Minehan

2016

Acc. Chem. Res.

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Electron-rich alkynes, such as ynamines, ynamides, and ynol ethers, are functional groups that possess significant potential in organic chemistry for the formation of carbon-carbon bonds. While the synthetic utility of ynamides has recently been expanded considerably, 1-alkynyl ethers, which possess many of the reactivity features of ynamides, have traditionally been far less investigated because of concerns about their stability. Like ynamides, ynol ethers are relatively unhindered to approach by functional groups present in the same or different molecules because of their linear geometry, and they can potentially form up to four new bonds in a single transformation. Ynol ethers also possess unique reactivity features that make them complementary to ynamides. Research over the past decade has shown that ynol ethers formed in situ from stable precursors engage in a variety of useful carbon-carbon bond-forming processes. Upon formation at -78 °C, allyl alkynyl ethers undergo a rapid [3,3]-sigmatropic rearrangement to form allyl ketene intermediates, which may be trapped with alcohol or amine nucleophiles to form γ,δ-unsaturated carboxylic acid derivatives. The process is stereospecific, takes place in minutes at cryogenic temperatures, and affords products containing (quaternary) stereogenic carbon atoms. Trapping of the intermediate allyl ketene with carbonyl compounds, epoxides, or oxetanes instead leads to complex α-functionalized β-, γ-, or δ-lactones, respectively. [3,3]-Sigmatropic rearrangement of benzyl alkynyl ethers also takes place at temperatures ranging from -78 to 60 °C to afford substituted 2-indanones via intramolecular carbocyclization of the ketene intermediate. tert-Butyl alkynyl ethers containing pendant di- and trisubstituted alkenes and enol ethers are stable to chromatographic isolation and undergo a retro-ene/[2 + 2] cycloaddition reaction upon mild thermolysis (90 °C) to afford cis-fused cyclobutanones and donor-acceptor cyclobutanones in good to excellent yields and diastereoselectivities. This process, which takes place under neutral conditions and proceeds through an aldoketene intermediate, obviates the need to employ moisture-sensitive and/or unstable acid chlorides under basic conditions for intramolecular [2 + 2] cycloaddition reactions. Furthermore, Lewis acid-catalyzed intramolecular condensations of both ethyl and tert-butyl ynol ethers with tethered acetals efficiently provide protected five-, six-, and seven-membered cyclic Baylis-Hilman adducts. Metalated ethoxyacetylene can also participate in multiple bond-forming reactions that avoid isolation of the alkynyl ether intermediate. Lewis acid-promoted tandem additions employing epoxides/oxetanes and carbonyl compounds give rise to (Z)-α-alkylidene and α-benzylidene lactones stereoselectively in high overall yields. Three new carbon-carbon bonds and a ring are formed in this atom-economical single-flask transformation, resulting in a significant increase in molecular complexity. This Account provides a detailed overview of these...

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Section: Thermal Retro-ene/[2 + 2] Cycloaddition Reactions Of Tert-bu...supporting

confidence: 82%

Section: Thermal Retro-ene/[2 + 2] Cycloaddition Reactions Of Tert-bu...mentioning

confidence: 99%

Tandem Bond-Forming Reactions of 1-Alkynyl Ethers

Minehan

2016

Acc. Chem. Res.

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“…Analytical data agreed with those reported in the literature. [28] Methyl 2-[tert-butoxycarbonyl(3-methylpent-4-enyl)amino]acrylate (17): This compound was synthesized from 5 and 15, following general procedure B; colorless oil; yield: 553 mg (77 %). (18): This compound was synthesized from 5 and 16, following general procedure B; colorless oil; yield: 281 mg (64 %).…”

Section: -Iodo-3-methylpent-1-ene (15)mentioning

confidence: 99%

“…Work-up after this step was carried out by pouring the mixture into a cold HCl solution, separating the organic phase, extracting the aqueous phase with Et 2 O and concentrating the combined organic phases; colorless liquid; yield of 26: 205 mg (48 % over 2 steps). (27) General Procedure E for Ring-Closing Metathesis of 8, [28][29][30] A solution of the substrate in toluene (~3 mm) was stirred under an inert atmosphere at 80 8C. Catalyst A (5 mol %) was added and the reaction mixtuire was stirred at 80 8C for 1 h. Next, a second portion of A (5 mol %) was added and the reaction mixture was stirred overnight at 80 8C.…”

Section: General Procedures D For the Transformation Of Ethyl Esters Imentioning

confidence: 99%

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A Ring‐Closing Metathesis Approach to Cyclic α,β‐Dehydroamino Acids

et al. 2008

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A comprehensive study on the synthesis and ring-closing metathesis (RCM) of a,b-dehydroamino acids is described. This sequence has led to the formation of a range of biologically relevant functionalized nitrogen heterocycles. The incorporation of chiral building blocks in the RCM precursors eventually resulted in the formation of optically active 4-substituted cyclic dehydroamino acids. In ad-dition, olefin isomerization under metathesis conditions was observed for a number of compounds, which could be successfully inhibited either by the introduction of allylic substituents or by the addition of a ruthenium hydride scavenger. Scheme 1. Ring-closing metathesis of dehydroamino acids.Scheme 4. Synthesis of allylically substituted RCM precursors.Scheme 5. RCM of allylically substituted dehydroamino acid-based precursors.

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Ketene Cycloadditions

1994

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The reaction of ketene with itself was described almost simultaneously in 1908 by Chick and Wilsmore in England, and by Staudinger and Klever in Germany; priority for the discovery was attributed to Wilsmore by the German group. Ketene cycloaddition was an early example of a peculiar process, one that formed carbon–carbon bonds with ease, often without the need for solvent, catalyst, or high heat. Subsequent work by others was done in the shadow of Staudinger's exhaustive and rigorous study of all phases of ketene reactivity. Three factors led to a resurgence of interest in this reaction beginning in the 1960s. Haloketenes, which had previously eluded study, were found to have high reactivity, and the halogens could easily be removed after the reaction. The increasing sophistication of powerful analytical methods, particularly nuclear magnetic resonance spectroscopy, led to discovery of the interesting stereochemical aspects of this reaction. Finally, the new theory of orbital symmetry conservation provided a conceptual framework to rationalize these puzzling “no mechanism” reactions. This chapter is a review of cycloaddition reactions of ketenes. Here, a cycloaddition is defined as a reaction of a ketene with an unsaturated organic compound to give a cyclic product by a mechanism that, in principle, involves the almost simultaneous formation of two bonds between two reactants. While there is no concern here as to whether bond formation is concerted or stepwise, no other chemical process can take place between the formation of the first and second bond. Definition here involves both structural and mechanistic factors, and it is difficult to avoid a certain amount of arbitrariness. Products, such as dehydroacetic acid, which seem to us to arise by concatenation of ketene molecules followed by cyclization are excluded. These reactions, are more properly considered to arise from a series of ionic reactions, and the prediction of the eventual product does not take advantage of the special mechanistic features commonly associated with true cycloadditions. Additions to imines to give β‐lactams are numerous and will be covered in a separate review. The literature has been searched to the end of 1988. Many reviews devoted partially or exclusively to ketene cycloadditions have been published. Specific topics that have been reviewed include haloketenes, fluoroketenes, cyanoketenes, intramolecular cycloadditions, conjugated ketenes, and β‐lactam antibiotics. Ancillary topics pertinent to ketene cycloadditions that have been reviewed include cycloreversion reactions, ketene equivalents, which provide ketene functionality with olefin‐like reactivity especially in [4 + 2] reactions, application of frontier molecular orbital theory to cycloadditions, and a critical discussion of cycloadditions with polar intermediates. Applications of cyclobutanones in synthesis have also been reviewed.

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Type I intramolecular cycloadditions of vinylketenes

Cited by 39 publications

References 1 publication

Tandem Bond-Forming Reactions of 1-Alkynyl Ethers

Tandem Bond-Forming Reactions of 1-Alkynyl Ethers

A Ring‐Closing Metathesis Approach to Cyclic α,β‐Dehydroamino Acids

Ketene Cycloadditions

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