Process for preparing porphyrin derivatives, such as protoporphyrin (IX) and synthesis intermediates

A process for preparing a compound of formula (I), optionally in the form of a salt:

• in which:
• R is a hydrogen, —CH═CH2, —CH2—CH3, —CH(OH)CH3, —C(O)CH3, or —CH2CH2COOR′a,
• wherein R′a is hydrogen, methyl, ethyl, n-propyl, or i-propyl,
• R′ is hydrogen or R′b wherein R′b is methyl, ethyl, n-propyl or i-propyl,
• the method comprising:
• condensing, in an acidic medium, a compound of formula (II)
• in which R′b is as defined above for (I),
• with a compound of formula (III):
• in which R″ is selected from hydrogen, —CH═CH2, —CH2—CH3, —CH(OH)CH3, —C(O)CH3, —CH2CH2OH, —CH2CH2OC(O)CH3 and —CH2CH2Cl or —CH2CH2COOR′a, wherein R′a is hydrogen, methyl, ethyl, n-propyl, or i-propyl, so as to form the compound of formula (I′):
• in which R″ and R′b are as defined above for (II) and (III),
• and,
• when R″ and R are not the same moiety, further comprising converting R″ to R, and
• when R′═H, further comprising eliminating R′b so as to form —COOH moieties, optionally in the form of a salt.