The invention concerns: a) methyl-phenyl derivatives of general formula (I) wherein R1 represents OH, C3-C7 alkyl, or C3-C7 cycloalkyl, said compounds being in the form of individual isomers or mixtures thereof; b) the method for preparing them by reacting: either a hydroxylamine salt with an N-substituted o-(p-tolyl)-benzaldimine to obtain o-(p-tolyl)-benzaldoxime; or an N-substituted 2-halobenzaldimine with a p-tolylmagnesium halide in the presence of a manganese mineral derivative, to obtain the compounds of formula (I) wherein R1 represents C3-C7 alkyl or C3-C7 cycloalkyl; c) their use for preparing o-(p-tolyl)-benzonitrile, intermediate in the synthesis of medicines.