Catalytic synthesis of homoallyloxyalcohols and 1,2-bis(homoallyloxy)ethanes through ring-opening allylation of cyclic acetals with allylsilanes over solid acids

Abstract

Ring-opening allylation of cyclic acetals with allylsilanes afforded silyl ethers using a silica–alumina catalyst. For example, the reaction of 2-phenyl-1,3-dioxolane with allyltrimethylsilane gave the corresponding silyl ether in 83% yield. After the allylation, addition of water to the reaction mixture allowed hydrolysis of the silyl ether to afford the homoallyloxyalcohol in 77% yield based on the acetal used. The reaction pathway of the silica–alumina-catalyzed allylation was examined. Solid-state ¹³C and ²⁹Si NMR analyses revealed the generation of SiMe₃ groups on the silica–alumina surface. The part of the (surface)–O–SiMe₃ groups was found to be an active site for the allylation reaction. During the silica–alumina-catalyzed allylation, a small amount of 1,2-bis(homoallyloxy)ethane formed as a co-product. The selectivity toward the 1,2-bis(homoallyloxy)ethane increased from 7% to 60% using H⁺-montmorillonite instead of silica–alumina. Detailed reaction pathways for the syntheses of 1,2-bis(homoallyloxy)ethanes were also investigated.