A method of preparing the anthracyclin carminomycin using a starting material comprising daunorubicin. The method comprises reacting daunorubicin or N-protected daunorubicin with soft Lewis acids for the demethylation of the 4-methoxy group, resulting in a reaction mass. The reaction mass is treated with an aqueous solution of a strong organic acid or a mineral acid. After decomposition of the resulting carminomycin and Lewis acids reactive complex, the reaction mass is extracted using a water insoluble organic solvent. As a result, carminomycin is extracted as a base.