A process for preparing (E)-(5,6-dihydro-1,4,2-dioxazin-3-yl)(2-hydroxyphenyl)methanone O-methyl oxime (13) or (Z)-(5,6-dihydro-1,4,2-dioxazin-3-yl)(2-hydroxyphenyl)methanone O-methyl oxime (15) which includes: (a) reacting compound (10) with an alkyl nitrite in the presence of an acid to form compound (11A) or reacting compound (10) with an alkyl nitrite in the presence of a base to form compound (11B); (b) reacting compound (11A) with 2-haloethanol to form compound (12A) or reacting compound (11B) with 2-haloethanol to form compound (12B); and (c) reacting compound (12A) with a base to form compound (13) or reacting compound (12B) with a base to form compound (15).