Ion-cyclotron resonance studies of the reactions between ethers and the trimethylsilyl cation

Abstract

Nucleophilic attack of a dialkyl ether (R–O–R′) at the electrophilic silicon centre of the trimethylsilyl cation (Me₃Si⁺) produces the 1 : 1 adduct Me₃Si–ORR′. The adduct generally decomposes by elimination of a neutral fragment. When R > Me, the adduct undergoes characteristic elimination of the olefin (R–H·). When R′ > R, the adduct eliminates the larger olefin preferentially. This elimination proceeds by β-hydrogen transfer to oxygen through a four-membered transition state, with the hydrogen transfer being involved in the rate-determining step. When R = Me and R′= CH₂CH₂F, an entirely different decomposition channel is noted, i.e. Me₃SiF is eliminated. The adducts from cyclic ethers generally fragment to Me₃Si–OCH₂, except for adducts derived from ethylene oxide derivatives, which do not decompose.