The oxidative magnesiation of nitrogen-containing pi-deficient halogenoheteroaromatics using active magnesium was accomplished. Both magnesiation followed by addition of a carbonyl compound (Grignard reaction) and magnesiation in the presence of a carbonyl compound (Barbier reaction) were carried out to afford the corresponding product. Especially, the latter method enabled fused halogenodiazines such as 4-chloro-1-phenyl-1H-pyrazolo[3,4-d]pyrimidine or 2-chloroquinoxaline to magnesiate at a mild temperature (-20 to 30 degrees C).