SILYL ENOL ETHER CATION RADICALS IN SOLUTION - NUCLEOPHILE ASSISTED SI-O BOND-CLEAVAGE

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.