Thiazo rifamycins II

A mechanism for the reaction between rifamycin S and HS-CH2-CH(NH2)-R derivatives, leading to the formation of thiazole and thiazin-2-one rifamycin derivatives is proposed. It is shown that the ringcontraction thiazine thiazole occurs with extrusion of the CH2 group to the S atom, while the formation of the thiazole and the thiazin-2-one rifamycins depends on the nature of the R group.