Hydrophobic species-enabled acid–base multi-catalysis for stereoselective access to renewable trans-anethole?

Dalton Transactions Pub Date: 2022-10-12 DOI: 10.1039/D2DT02502G

Abstract

trans-Anethole (trans-AN) is widely applied in food, daily necessities, and pharmaceuticals and is typically available from inefficient natural oil extraction or complex organic transformations over mineral acid or noble metals. Here, a green and sustainable route was developed to stereoselectively produce trans-AN (ca. 90% selectivity) over an organic polymeric phosphonate–hafnium catalyst (PAS–Hf) through the cascade transfer hydrogenation and dehydration of biomass-based 4′-methoxypropiophenone (4-MOPP), with an environmental impact factor (E-factor) of 47.73. The porous structure and the enhanced hydrophobicity of the spherical catalyst PAS–Hf ensured the formation of more accessible and stable Lewis (Hf4+) and Br?nsted (SO3H) acid active sites, which could be used for rapid conversion of biomass-based 4-MOPP to AN (100% conversion, 97.2% yield) in 0.5–2 h (TOF: 9.3 h?1). Density functional theory (DFT) calculations elucidated that the addition of PAS–Hf could remarkably facilitate the overall conversion process by decreasing the reaction energy barrier (151.33 to 48.27 kJ mol?1) of the rate-determining step. The good thermal stability and heterogeneity of the bifunctional catalyst were responsible for its constant activity during at least five consecutive cycles. The synergistic/relay catalysis of Lewis acid–base and Br?nsted acid species could be extended to more than ten kinds of aldehydes and ketones. This acid–base multi-catalytic protocol has considerable potential in cascade biomass conversion via heterogeneous catalysis without any base additive.

Graphical abstract: Hydrophobic species-enabled acid–base multi-catalysis for stereoselective access to renewable trans-anethole
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