The cationic rearrangement of (3-Hydroxy-1-propenyl)tris(trimethylsilyl)-silanes into (1-trimethylsilyl-2-propenyl)bis(trimethylsilyl)silanols-experimental and theoretical studies

摘要

(3-Hydroxy-1-propenyl)tris(trimethylsilyl)silanes (Me_3Si)_3SiCH=CHCR_2OH (8b,c) (b: R = Me; c: R = Ph) undergo a rapid rearrangement involving a 1,2-Si,C migration of one trimethylsilyl group from the central silicon atom to a cationic neighboring carbon atom and a shift of the olefinic double bond, in the presence of acid, to afford (1-trimethylsilyl-2-propenyl)bis(trimethylsilyl)silanols (Me_3Si)_2Si(OH)CH(SiMe_3)CH=CR_2 (13b,c). Treatment of 8b,c with sulfuric acid in methanol gives the methoxysilanes (Me_3Si)_2Si(OMe)CH(SiMe_3)CH=CR_2 (14b,c). In a related reaction, 8b,c are converted by boron trifluoride into the fluorosilanes (Me_3Si)_2SiFCH(SiMe_3)CH=CR_2 (15b,c). A possible mechanism of the isomerization reaction, involving the rearrangement of the silylcarbenium ions [(Me_3Si)_3SiCH=CHCR_2]~+ into the silylium ions [(Me_3Si)_2SiCH(SiMe_3)CH=CR_2]~+, is proposed. This si supported by calculations, which indicate the higher stabilty of the silylium ion 10b compared with the isomeric silylcarbeniu m cation 9b. For 14c the results of an X-ray structural analysis are given.