The reaction at room temperature of an aldehyde with excess pyrrole in the absence of solvent affords the meso-substituted dipyrromethane. The reaction is catalyzed with trifluoroacetic acid or with BF9,0(Et)2. The dipyrromethaue is purified by crystallixation or by flash chromatography on silica with eluants containing 1% triethylamine. The reaction is compatible with aliphatic or aromatic aldehydes, including 2,6disubstituted benraklehydes. Nine dipyrromethanes have been prepared in this manner in yields of 47-865, indicating the broad scope of tbe reaction. The dipyrromethanes are stable in the purified form in the absence of light and air. Similar reaction with terephthalaldehyde and pyrrole affords the correspondmg bis-dipyrromethane. The reaction of a mesosubstituted dipyrrometbane with an aldehyde muter the conditions of the two-step one-flask porphyrin synthesis affords a direct route to trans-substituted meso-porphyrins. Acidolysis of the dipyrromethane is negligible under the conditions of the porphyrin-forming reaction. Four porphyrins bearing peripheral functional groups and faciallyencumbering groups have been prepared which serve as key building blocks in the synthesis of linear porphyrin aoays.