Efficient synthesis of styrene derivatives through ethenolysis of renewable propenylbenzenes

De Novo Biosynthesis of 4-Vinylanisole in Engineered Escherichia coli

4-Vinylanisole is an aggregation pheromone of the locust. Both gregarious and solitary locusts exhibit a strong attraction toward 4-vinylanisole, irrespective of gender or age. Therefore, 4-vinylanisole can be used for trapping and monitoring locusts. In this study, the construction of a de novo 4-vinylanisole pathway in Escherichia coli has been demonstrated for the first time. Subsequently, by increasing the supply of precursor substrates, we further improved the biosynthesis of 4-vinylanisole. Finally, a two-phase organic overlay culture was used to increase the titer to 206 mg/L. It presents a sustainable and ecofriendly alternative for the synthesis of 4-vinylanisole.

Inhibition of the Decomposition Pathways of Ruthenium Olefin Metathesis Catalysts: Development of Highly Efficient Catalysts for Ethenolysis

Ruthenium-based Hoveyda-type olefin metathesis catalysts bearing novel rigid spirocyclic alkyl amino carbenes (CAACs) have been developed. They are characterized by exceptional stability toward decomposition through β-elimination and bimolecular pathways, thus enabling unprecedented efficiency in the cross-metathesis of seed oil-derived fatty acid esters with ethylene (ethenolysis). Catalyst loading as low as 100 ppb was applied to the ethenolysis of the model substrate methyl oleate, leading to a remarkable turnover number (TON) of 2.6 million, significantly higher than previously reported (TON 340 000 at 1 ppm and 744 000 at 0.5 ppm catalyst loading). Ethenolysis of methyl esters derived from high oleic sunflower oil and rapeseed oil, readily available on an industrial scale, inexpensive, and renewable feedstocks, was for the first time effectively carried out with 0.5 ppm catalyst loading with TON as high as 964 000.

Methylene Capping Facilitates Cross-Metathesis Reactions of Enals: A Short Synthesis of 7-Methoxywutaifuranal from the Xylochemical Isoeugenol

Four combinations of type-I olefins isoeugenol and 4-hydroxy-3-methoxystyrene with type-II olefins acrolein and crotonaldehyde were investigated in cross-metathesis (CM) reactions. While both type-I olefins are suitable CM partners for this transformation, we observed synthetically useful conversions only with type-II olefin crotonaldehyde. For economic reasons, isoeugenol, a cheap xylochemical available from renewable lignocellulose or from clove oil, is the preferred type-I CM partner. Nearly quantitative conversions to coniferyl aldehyde by the CM reaction of isoeugenol and crotonaldehyde can be obtained at ambient temperature without a solvent or at high substrate concentrations of 2 mol·L^-1 with the second-generation Hoveyda-Grubbs catalyst. Under these conditions, the ratio of reactants can be reduced to 1:1.5 and catalyst loadings as low as 0.25 mol % are possible. The high reactivity of the isoeugenol/crotonaldehyde combination in olefin metathesis reactions was demonstrated by a short synthesis of the natural product 7-methoxywutaifuranal, which was obtained from isoeugenol in a 44% yield over five steps. We suggest that the superior performance of crotonaldehyde in the CM reactions investigated can be rationalized by "methylene capping", i.e., the steric stabilization of the propagating Ru-alkylidene species.

The first one-pot metathesis–hydroformylation procedure: a straight synthesis of 2-arylpropanals from renewable 1-propenylbenzenes

2-Arylpropanals are synthesised from renewable 1-propenylbenzenes via a two-step, one-pot procedure.