Catalytic cascade gas-phase heterocyclization of lactic acid and aniline into quinolones over mesoporous Hβ zeolite

Cascade reactions are an important synthetic strategy for efficient and rapid access to molecular complexity in chemical synthesis. In this study, the vapor-phase cascade heterocyclization was further developed, starting with the coupling of biomass-derived lactic acid with aniline to yield high-value quinoline derivatives. Mesoporous Hβ zeolite was employed as an eco-friendly heterogeneous catalyst, which was prepared via zeolitic dissolution–recrystallization treatment to generate abundant mesopore volume. The assessment of the catalyst activity and stability confirmed that the presence of mesopores within the zeolite significantly improved the life of the catalyst. This enhancement was primarily attributed to the facilitated diffusion of the bulky quinoline products through the pore channels of the mesoporous Hβ zeolite, which mitigates the formation of the coke deposits. Notably, the deactivation of the catalyst was reversible, and its catalytic activity could be almost entirely restored through simple calcination in air to eliminate the coking. Furthermore, this work elucidated the plausible mechanisms relating to the generation of diverse quinoline derivatives and byproducts from the reaction between lactic acid and aniline, which contribute to a better understanding of the complex reaction pathways involved in this cascade synthetic approach.