4-methyl-7-hydroxycoumarin (5 g, 28.4 mmol) and p-toluidine (3 g, 28.0 mmol) were separately dissolved in 1,4-dioxane (100ml each) . Paraformaldehyde (1.7g, 54.8 mmol) and  NaOH (0.1 g) were dissolved in methanol (3 ml) with heating. This solution was added to the cold 1,4-dioxane solution of p-toluidine. This combined solution was poured into the 4-methyl-7-hydroxycoumarin solution and heated to reflux for 24 h. At the end of the reaction, dioxane was distilled off and the remaining solid was dissolved in chloroform, and washed successively with 0.1 N K₂CO₃ solution and deionized water until the light blue colour of the water phase disappeared. Subsequently, the organic layer was dried with anhydrous Na₂SO₄ and chloroform was evaporated to yield crude benzoxazine-coumarin. Recrystallization from minimum amount of THF in a refrigerator gave white crystals. (56% yield)

The reaction most probably takes about 6-8 h,  however I left it 24 h. 

Baris Kiskan, Yusuf Yagci, Thermally Curable Benzoxazine Monomer with a Photodimerizable Coumarin Group, J. Polym. Sci. Part A: Polym. Chem., 2007, 45, 1670–1676.