Regioselective carbon-oxygen bond cleavage reactions of aromatic ethers and esters with potassium metal/18-crown-6/THF as the electron-transfer reagent

The facile carbon-oxygen bond cleavage reactions of a variety of aromatic ethers and esters were studied with an electron-transfer reagent that consisted of potassium metal and 18-crown-6 in tetrahydrofuran (THF). The relative rates of carbon-oxygen bond cleavage, with these aromatic ethers and esters under electron-transfer conditions, was studied in competition with the standard, diphenyl ether. The order of relative reactivities was as follows: phenyl 2-hydroxybenzoate (10) (>2.0); phenyl 2-methoxybenzoate (11) (>2.0); phenyl 4-methoxybenzoate (12) (>2.0); 2-methoxyphenyl benzoate (13) (>2.0); 4-methoxyphenyl benzoate (14) (>2.0); 4-hydroxyphenyl benzoate (15) (1.6); benzyl benzoate (9) (1.3); 4-methoxyphenyl phenyl ether (5) (1.15); phenyl benzoate (8) (1.04); diphenyl ether (1) (1.0); dibenzyl ether (2) (0.98); 2-methoxyphenyl phenyl ether (6) (0.97); benzyl phenyl ether (3) (0.96); phenethyl phenyl ether (7) (0.77); and 4-hydroxyphenyl phenyl ether (4) (