Methyl 3-substituted 131-deoxo-pyropheophorbides-a possessing the 7-methyl group were transformed into the corresponding 131-deoxo-pyropheophorbides-b bearing the 7-formyl group via the regioselective mono-dehydration of cis-7,8-diols to 7-hydroxymethyl-chlorins under mild acidic conditions. The exclusive production of the 71-hydroxy-chlorins without detection of the 81-hydroxy-chlorins in the reaction mixture did not depend on the 3-substituents. The regioselectivity was regulated by the 13-functional groups, and the ratio of the 81-OH over 71-OH products enhanced with an increase of the group electronegativity. Methyl mesopyropheophorbide-b (7-formyl-131-oxo-chlorin) was efficiently obtained by modifying methyl mesopyropheophorbide-a, one of the chlorophyll-a derivatives, through the protection of the 131-oxo moiety and the aforementioned mono-dehydration. The effects of the 7-substituents on the visible absorption spectra in a solution were comparable to those of naturally occurring, photosynthetically active chlorophylls-a/b and bacteriochlorophylls-c/e bearing the 7-methyl/formyl groups.