The reaction of tert-butylamine (I) with formaldehyde gives N-methylene-tert-butylamine (II), which is condensed with rifamycin SV (III) by means of MnO2 in THF yielding 3-formylrifamycin SV (IV). Finally, this compound is treated with hydrazine and piperidyl chloroformiminium chloride (V) in THF.