P 5 P 6 Mechanistic Studies of the Reactions of Transient Silylene - Thf Complexes with Acids , Bases and an Alkene in Thf / Hexanes Mixtures

Quinols (5a-c) generate the corresponding aryloxenium ions (6a-c) reversibly at pH 1.0 (0.1M HClO4, 30C) although they are stable for a duration of at least 2-3 weeks at pH 4.6 and pH 7.1 at 30C. Kinetics of decomposition of the parent quinols has been monitored by HPLC in the presence and absence of a trapping agent, Br. In the presence of Br, both bromo adduct and dienonephenol rearranged product is formed at the same rate. Changing the pH to 2 causes a 10 fold decrease in rate of both decomposition of the starting quinol and generation of rearranged product and bromo adduct. The quinols have previously been shown to be the major products of the reaction of the oxenium ions with water. These observations are consistent with the reversible formation of aryloxenium ions from their parent quinol in a rate-limiting step that is catalysed by H.