Silyl enol ether cation radicals in solution: nucleophile assisted Si–O bond cleavage

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Abstract
The sterically hindered silyl enol ethers 1–3 have been synthesised and the structure of the sterically most congested representative, i.e. 2, has been elucidated by X-ray analysis. The corresponding cation radicals 1˙+, 2˙+ and 3˙+ have been generated in solution through electrochemical and chemical electron transfer. The one-electron oxidation with 2 equivalents of [Fe(phen)3](PF6)3 furnished in all three cases 3-mesityl-4,6,7-trimethyl-2-phenylbenzofuran 4 in high yield. In cyclic voltammetry experiments the kinetics of the Si–O bond cleavage in the silyl enol ether cation radicals in dichloromethane and acetonitrile have been determined in the presence of various nucleophiles (methanol, 2-methylpropan-2-ol, pyridine and 2-bromopyridine) From the data, a nucleophile assisted Si–O bond cleavage mechanism has been inferred.