Reaction of 3-formylrifamycin SV with formalin in combination with primary alkylamines.

3-Formylrifamycin SV (4) was found to react with formalin in combination with primary alkylamines to give 2, 3-dihydropyrimido [4, 5-b] rifamycin derivatives 3. The iminium carbon of 3 was found to be reduced when primary alkylamines with at least one hydrogen atom at the α-position were used. The addition of an alcoholic OH group to the iminium carbon of 3 is also described.