The effect of an alkoxy group on the kinetic and thermodynamic acidity of benzene and toluene

Article abstract of DOI:10.1016/S0040-4020(98)83011-1

2-, 3- and 4-Methoxytoluene can be selectively metalated at an O-adjacent ortho position when butyllithium or tert-butyllithium in the presence of sodium (potassium) tert-butoxide or N,N,N',N'',N''-pentamethyldiethylenetriamine are employed as reagents. In contrast, lithium diisopropylamide or lithium 2,2,6,6-tetramethylpiperidide deprotonate the benzylic α-position of 2- and 3-methoxytoaluene exclusively and of 4-methoxytoluene preferentially. These relative reactivities can be rationalized by an interplay of transition state stabilizing and destabilizing forces (dipole matching and metal coordination vs. lone pair repulsion).