Evidence for Silicon-Directed Acid-Catalysed Ring Opening of a β,γ-Epoxy Silane: Reaction of 1,1-Dimethyl-1-silacyclohex-3-ene Oxide With p-Nitrobenzoic Acid

Abstract

The ring-opening reaction of the β,γ-epoxy silane (4) with p-nitrobenzoic acid in chloroform occurs regiospecifically to give the two hydroxy esters (14) and (15). The mechanism involves regiospecific ring opening giving the β-silicon-stabilized carbenium ion (18) which is captured by the p-nitrobenzoate counter ion. The solution conformation of (14) provides evidence for the presence of σC- Si -σ* C-O interactions between the ring C- Si bonding orbital and the C-OCOC₆H₄NO₂ antibonding orbital. In acetone, reaction of (4) with p-nitrobenzoic acid takes a different pathway and results in acyclic products from solvent attack at the silicon.