A new method was developed for synthesizing benzoxazine derivatives by O-alkylation or 2,6-ditert-butyl-4-(o-hydroxyphenylimino)-2,5-cyclohexadienones with allyl or benzyl halides and subsequent thermal heterocyclization of allyl or benzyl ethers thus formed. The cyclization of ethers derived from 2,6-ditert-butyl-4-(o-hydroxyphenylimino)-2,5-cyclohexadienones and phenacyl bromides or diethyl bromomalonate is so fast that these compounds cannot be isolated.