Why is furan reactive diene

Our experimental observations of the lack of reaction of the non-fluorinated dienophile, the stereochemical outcomes, and the rate acceleration accompanying furan methylation are all well predicted by our calculations. The calculated free energy barriers generally correlate well with measured reaction rates, supporting a reaction mechanism in which zwitterionic character is developed strongly.

An in situ ring opening reaction of exo -cycloadduct ethyl exo N , N -diethylcarbamoyloxy -3,3-difluorooxabicyclo[2. Substantial steric opposition to Lewis acid binding prevents carbonate formation from 2-substituted furans. In papers with more than one author, the asterisk indicates the name of the author to whom inquiries about the paper should be addressed. Kinetic data, coordinates angstrom of stationary structures on the potential energy surface of the reaction of furan 7a with dienophile 6a.

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The Journal of Physical Chemistry A , 24 , Arylglyoxals in Synthesis of Heterocyclic Compounds. Chemical Reviews , 5 , The Journal of Organic Chemistry , 78 6 , Wilson , Jonathan M. Percy , Joanna M. Redmond , and Adam W. The Journal of Organic Chemistry , 77 15 , Journal of Physical Organic Chemistry , 32 6 , e Journal of Physical Organic Chemistry , 32 5 , e Computational and Theoretical Chemistry , , Journal of Physical Organic Chemistry , 30 6 , e Ring Rearrangement Metathesis in 7-Oxabicyclo[2.

Some Applications in Natural Product Chemistry. Natural Product Communications , 12 5 , X Journal of Molecular Graphics and Modelling , 70 , Mojtahedi , M. The key to success is the use of aqueous medium, which supplies an additional thermodynamic driving force by coupling the unfavorable DA equilibrium to the exergonic hydration of the carbonyl functionality in the adducts to form geminal diols.

This finding enables the direct access to various novel DA adducts derived from renewable furfurals and maleimides, via a mild, simple and environmentally-friendly synthetic protocol. Cioc, M. Lutz, E. Pidko, M. Crockatt, J. Bruijnincx, Green Chem. You can use material from this article in other publications, without requesting further permission from the RSC, provided that the correct acknowledgement is given and it is not used for commercial purposes.

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Read more about how to correctly acknowledge RSC content. Fetching data from CrossRef. This may take some time to load. Loading related content. This approach enables Diels—Alder reactions to be performed under very mild conditions, even with highly unreactive dienes such as 2,5-furandicarboxylic acid.

The obtained DA adducts of furoic acids are shown to be versatile synthons in the conversion to various saturated and aromatic carbocyclic products. Conversely, Diels—Alder reactions involving electron-poor derivatives such as furoic acids furans substituted with a COOH group are very much underexplored.

Furoic acids are readily available via renewable platform molecules such as furfural and 5-hydroxymethyl furfural 5-HMF. Unfortunately, only a handful of recent reports describe attempts to capitalize on these advantages. Instead, the vast majority of chemistry developed in this area relies on the well-established use of electron-rich furan dienes. While this conventional approach may be efficient for the individual DA step, it is often redox uneconomical overall, as exemplified for instance by the cycloaddition between 2,5-dimethyl furan and ethylene targeting renewable terephthalic acid Scheme 1A.

Relatedly, Sibi et al. To the best of our knowledge, there is a single study thoroughly investigating the reactivity of furoic acids in Diels—Alder chemistry.

Bowman et al. Interestingly, the authors note that reactivity could be tuned by solvent effects: rate and equilibrium conversions were significantly higher in water compared to reactions in dimethyl formamide. Encouraged by this precedent and following our interest in the development of synthetic applications based on the Diels—Alder chemistry of readily available oxygenated bio-based furans, 33,34 we decided to investigate 2-furoic acids as underexplored class of dienes. Next, we turned our attention to water as solvent.

The rate-enhancement ability of water in Diels—Alder chemistry is well known and many arguments have been proposed to explain it. The reaction also clearly benefited from the synergy of using aqueous solvent and the base effect: nearly quantitative yield of 1a was obtained when the cycloaddition was performed in water in the presence of 1 equiv. The reaction profiles depicted in Fig. In addition, the system is nearly at equilibrium within 12 h, which is not the case for the base-free experiment.

Importantly, the conversion of 1a was clean in both cases, with no side products originating from the diene detected. On the other hand, some hydrolysis of 2a towards maleic acid does occur, to a low extent, and if the NaOH stoichiometry is increased beyond the 1 : 1 ratio, the sodium salt of N -methyl maleamic acid is formed see also note In studying the reaction scope, we chose the conditions shown in entry 4, Table 2 with 1 equiv.

NaOH , with the aim of minimizing the amount of minor adduct endo - 3 and simplifying the isolation of a pure product following a general protocol. Thus, after reaction, the excess maleimide can be washed away and recovered with an organic solvent, while acidification of the aqueous phase typically leads to the selective precipitation of exo - 3. Higher homologues N -Ph, N -Cy proved problematic, however, due to poor solubility of the dienophile in the aqueous medium entries 4 and 5 ; the addition of a cosolvent MeOH was beneficial in this case entry 6 and although the conversion levels were moderate, synthetically useful yields of pure adducts 3d and 3e could be obtained without excessive adjustment of the general procedure.

Next, we proceeded with the investigation of the furan diene scope, with the focus on easily accessible biomass-derived 5-substituted 2-furoic acids.