A synthesis process for making a benzoxazine compound containing at least one benzoxazine unit from aromatic amine containing at least one primary amino group, at least one phenolic compound with at least one ortho-hydrogen, and alkyl formcel. In one embodiment, the aromatic amine is reacted with alkyl formcel to generate an alkoxymethyl intermediate compound. Subsequently, the intermediate compound is reacted with a phenol to generate the benzoxazine compound. In another embodiment, the benzoxazine compound is formed by reacting aromatic amine with alkyl formcel and phenol in one reaction step. Also disclosed is a method for isolating the alkoxymethyl compound formed by reacting aromatic amine with alkyl formcel. The isolated alkoxymethyl compound is useful as a reactant in a subsequent reaction.