Photochemical protodesilylation of 2-R3Si-1,3-dimethoxybenzenes. Direct observation of .beta.-silyl-substituted cyclohexadienyl cations

Abstract

Irradiation (254 nm) of the title compounds 5 (R 3 Si=Me 3 Si, Ph 2 MeSi, and 4-XC 6 H 4 Me 2 Si with X= 4-MeO, 4-Me, H, 4-F, and 4-Cl) in 1,1,1,3,3,3-hexafluoroisopropyl alcohol (HFIP) results in quantitative conversion to 1,3-dimethoxybenzene and the ether R 3 SiOCH(CF 3 ) 2 . This reaction proceeds via selective protonation at the 2-position of excited 5 to give an intermediate 1-R 3 Si-2,6-dimethoxybcnzenium ion, 6. These cations are detected as transients following 248-nm laser flash photolysis (LFP) and represent the first examples of β-silyl-substituted cyclohexadienyl cations observed either with LFP or under stable-ion conditions