The process is carried out by reacting 3-methoxybenzenethiol and ??-bromo-4-methoxyacetophenone in the presence of a strong base at a relatively low temperature, to form ??-(3-methoxyphenylthio)-4-methoxyacetophenone, which is then ring-closed with an agent such as polyphosphoric acid at a high temperature to obtain the desired starting compound.