Understanding the effect of allylic methyls in olefin cross-metathesis

Courchay, Florence C.; Baughman, Travis W.; Wagener, Kenneth B.

doi:10.1016/j.jorganchem.2005.09.030

Cited by 20 publications

(8 citation statements)

References 59 publications

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“…Stereocontrol via hydrogen bonding, proposed by Hoveyda and co-workers 87. Wagener and co-workers have investigated the effects of allylic methylation with precatalysts G1 and G2 88. Each pre-catalyst was in turn exposed to ca.…”

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confidence: 99%

The Influence of Structure on Reactivity in Alkene Metathesis

Nelson

Percy

2014

Advances in Physical Organic Chemistry

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Alkene metathesis has grown from a niche technique to a common component of the synthetic organic chemistry toolbox, driven in part by the development of more active catalyst systems, or those optimized for particular purposes. While the range of synthetic chemistry achieved has been exciting, the effects of structure on reactivity have not always been particularly clear, and rarely quantified. Understanding these relationships is important when designing new catalysts, reactions, and syntheses. Here, we examine what is known about the effect of structure on reactivity from two perspectives: the catalyst, and the substrate. The initiation of the pre-catalyst determines the rate at which active catalyst enters the catalytic cycle; the rate and selectivity of the alkene metathesis reaction is dependent on how the substrate and active catalyst interact. The tools deployed in modern studies of mechanism and structure/activity relationships in alkene metathesis are discussed.

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confidence: 99%

The Influence of Structure on Reactivity in Alkene Metathesis

Nelson

Percy

2014

Advances in Physical Organic Chemistry

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“…We have described a general model for selectivity in CM,3h but a number of limitations still hinder its widespread application in organic synthesis. One of those issues is the tolerance of steric conjestion on or around the reactive olefin moiety 4a. Wagener and co-workers have described the challenge of even simple allylic methyl substituents in CM with both Ru- and Mo-based catalyts 4b…”

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confidence: 99%

Increased Efficiency in Cross-Metathesis Reactions of Sterically Hindered Olefins

2008

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GENERAL INFORMATIONNMR spectra were recorded on an Oxford 300 MHz NMR spectrometer running Varian VNMR software. Chemical shifts are reported in parts per million (ppm) downfield from tetramethylsilane (TMS) with reference to internal solvent for 1 H NMR and 13 C NMR spectra. Chemical shifts are reported in parts per million (ppm) downfield from H 3 PO 4 for 31 P NMR spectra. Multiplicities are abbreviated as follows: singlet (s),, and broad (br). Analytical thin-layer chromatography (TLC) was performed using silica gel 60 F254 precoated plates (0.25 mm thickness) with a fluorescent indicator. Visualization was performed with standard potassium permanganate stains or UV light. Flash column chromatography of organic compounds was performed using silica gel 60 (230-400 mesh). All glassware was either oven dried or flame dried, and reactions were done under an atmosphere of argon unless otherwise noted. All organic solvents were dried by passage through solvent purification columns containing activated alumina. All commercial chemicals were used as obtained. GENERAL CROSS METATHESIS PROCEDUREA 10 mL 2-neck round bottom flask was charged with a stir bar and outfitted with a reflux condenser and a septum. The apparatus was flame-dried under active vacuum, and then allowed to cool to ambient temperature under a positive pressure of argon. The flask was then charged the catalyst (0.025 mmol) as a solid. Dry, degassed CH 2 Cl 2 (2.0 mL) was then added via syringe. The substrates (0.5 mmol of limiting olefin reagent)were then added simultaneously via syringe to the stirring solution. The septum was replaced with a glass stopper, and the solution was heated to reflux for the indicated amount of time. After cooling to ambient temperature, ethyl vinyl ether (0.5 mL) was

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“…We were confident that the initial cross metathesis would take place on the least substituted terminal alkenyl group (releasing styrene ultimately), so that the difference in the rate of consumption of 8ab and 8ac reflects steric hindrance of RCM by the internal methyl group in 8ac. 17 The higher precatalyst loading required by 8bc represents a slow initial alkylidene transfer 18 and a hindered RCM. We were pleased to note that 8db and 9db were reactive and underwent RCM in good yields, despite the significant steric hindrance to initial alkylidene transfer.…”

Section: Scheme 1 Concept Of Difluorinated Carbasugars As Potential Pmentioning

confidence: 99%