Platform approach to diversification: Bio-based methyl coumalate to functionalized aromatics via a Diels--Alder strategy.

摘要

The chemical industry relies on crude oil to manufacture the vast majority of chemicals. However, the increasing demand cannot be supported with the simultaneous decrease in natural crude oil reserves and increasing prices. Green chemistry solutions may resolve the issue utilizing biorenewable feedstocks, especially for the functionalized aromatic compounds that are ubiquitous in a wide variety of consumer materials. The atom economical Diels-Alder reaction installs two carbon-carbon bonds with high levels of regio-, chemo-, and stereocontrol, which was effectively utilized in a platform approach.;Through metabolic engineering, glucose can be converted to malic acid. Afterwards, dimerization and esterification provided the 2-pyrone methyl coumalate as a platform molecule for the methodology. Although unactivated alkenes resulted in aromatic compounds, palladium was required, and with electron-deficient alkene dienophiles, mixtures of regioisomers were observed. In contrast, we developed an inverse electron-demand Diels-Alder/retro-Diels-Alder/elimination domino methodology from methyl coumalate with electron-rich olefins to regioselectively furnish diverse aromatic compounds.;Vinyl ether dienophiles provided a broad range of aromatic compounds, which were equipped with an alkoxy leaving group to facilitate aromatization without a catalyst. The scope was expanded with readily prepared acetal and orthoester dienophile equivalents that could be utilized in crude form. As practical bench-stable compounds, elimination occurred under the thermal conditions to reveal the dienophile. The metal-free, one-pot domino sequence efficiently provided high yields and regioselectivities for the desired aromatic compounds. The expansive range of accessible aromatic compounds through the methodology included carbazoles, tricyclic, fused, anisole, and biphenyl systems. Notably, captodative dienophile derivatives from methyl pyruvate provided a 100% biorenewable formal synthesis to terephthalic acid with dimethyl terephthalate as the intermediate. As commodity co-monomers for poly(ethylene terephthalate), the green methodology was further optimized to remove the reaction solvent and recrystallize the product in up to 95% yield. In summary, methyl coumalate represents a convenient bio-based platform for diverse aromatics which fulfills many green chemistry principles in the progress toward a sustainable future.