Zeolite Catalytic Simmons-Smith Cyclopropanation of Alkenes for the Synthesis of High-Energy-Density Fuels

Simmons-Smith cyclopropanation of alkenes is a universal reaction used to construct cyclopropyl groups in the synthesis of fine chemicals, medicines, and high-energy-density aerospace fuels. Organic acids such as trifluoroacetic acid (CF3COOH) are widely used to improve the reaction, but they have the disadvantages of being difficult to recycle and harmful to health and the environment. In this work, we reported that heterogeneous acidic zeolite can replace organic acids to catalyze the Simmons-Smith cyclopropanation with better activity. HZSM-5 shows higher conversion and yield than CF3COOH in the cyclopropanation of dicyclopentadiene and can be reused for recycled reaction. A catalytic mechanism involving Bronsted acid sites [Si(OH)Al] as the catalytic sites is proposed, which is verified by characterizations of a complex of zeolite with reactant in each step. Density functional theory (DFT) calculations show that HZSM-5 can reduce the energy barrier compared to CF3COOH, which explains why zeolite is more active. Activity assessment of different types of zeolites indicates that the amount of Bronsted acid sites is the key factor for cyclopropanation, and simple ball-milled HZSM-5 can further improve the activity because more acid sites are accessible for the reaction. Moreover, the zeolite performs well in the cyclopropanation of several cyclic and linear alkenes, especially for the synthesis of high-energy-density fuels, demonstrating that zeolite catalysis is a universal method to improve cyclopropanation. This work provides an efficient and environmentally friendly method for cyclopropanation.