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.