Catalytic Hydrogenation of meso-Octamethylporphyrinogen (Calix[4]pyrrole)

Hydrogenation of meso-octamethylporphyrinogen (calix[4]pyrrole) with a number of heterogeneous catalysts in different experimental conditions was investigated. GC-MS analyses of the reaction mixtures showed the formation of one to four products in low to moderate yields: three of them were diastereoisomers of the product coming from half-hydrogenation of the substrate, and displayed alternating pyrrolidine and pyrrole rings; one was the all-cis saturated product. Acidic medium was necessary to achieve hydrogenation, but a too strong acidic solvent or additive was detrimental to the stability of the substrate and/or the catalyst.