Process for preparing 5,6-dihydro-2-methyl-1,4-oxathiin derivatives

A process of preparing 5,6-dihydro-2-methyl-1,4-oxathiin derivative I of the formula ##STR3## wherein X is an amino group having the formula, ##STR4## wherein R and R' are the same or different and are selected from the group consisting of hydrogen, phenyl, alkyl having up to 15 carbon atoms, cyclohexyl, nitrophenyl, alkoxyphenyl in which the alkoxy group has up to 4 carbon atoms, benzyl, furfuryl, halophenyl, tolyl, naphthyl, biphenyl, or X is an alkoxy group--OR, in which R is primary, secondary or tertiary alkyl group having up to 6 carbon atoms;

• comprising treating the 1,3-oxathiolane IV of the formula:
• ##STR5## wherein X is the same as in the formula I, with halogen (chlorine or bromine) in a nonhydroxylic solvent at a temperature in the range between -60.degree. C. and room temperature whereby ring expansion takes place via a sulfenyl compound of the formula ##STR6## wherein Y is Cl or Br which cyclizes with loss of hydrogen halide to form the compound I, and subsequently isolating this from the resulting mixture.