A method for preparing a fused oxazinone is disclosed in which a carboxylic acid is contacted with a sulfonyl chloride and an isatoic anhydride in the presence of a tertiary amine, the nominal mole ratio of said sulfonyl chloride to said carboxylic acid being from about 1.0 to 1.5 and the nominal mole ratio of said isatoic anhydride to said carboxylic acid is from about 0.8 to 1.2. Also disclosed is a method for preparing a compound of Formula (III), using a compound of Formula (1a) that is characterized by preparing the fused oxazinone of Formula (1a) by the method above, using a compound of the formula LS(O).sub.2Cl as the sulfonyl chloride, a compound of Formula (2') as the carboxylic acid, and a compound of Formula (5') as the isatoic anhydride wherein L, X, Y and R.sup.1 through R.sup.9 are as defined in the disclosure ##STR00001##