Meso-alkylidenyl-thia(p-benzi)porphyrin and its ring expanded analog containing exocyclic C-C double bonds at meso-positions, undergo initial protonation at the exocyclic alkylidene alpha-carbon.

New core-modified, meso-alkylidenyl porphyrinoids bearing multiple exocyclic double bonds were synthesized and characterized. The synthesis was accomplished using a typical "3 + 1"-type condensation approach. Stable exocyclic tautomers bearing double bonds at the meso positions, as well the corresponding endocyclic tautomers, were isolated in the case of both thiabenziporphyrin and thiapyriporphyrin products prepared in the course of this study. On the other hand, only the exocyclic tautomer was isolated in the case of the congeneric oxapyriporphyrin and oxabenziporphyrin. Expanded analogues of the exocyclic forms of oxabenziporphyrin and thiabenziporphyrin were also isolated as minor products. A single-crystal X-ray diffraction analysis of the expanded thiabenziporphyrin (20) revealed that all four pyrrole rings displayed an inverted geometry, presumably reflecting the strong hydrogen-bonding extant between the pyrrole N-H proton and the carbonyl group of the malonate moiety in the solid state. On the other hand, the expanded oxabenziporphyrin (14) was found to possess a severely distorted geometry with only one pyrrole ring being inverted. Careful analysis of the structure revealed that the solid-state geometry of the expanded macrocycles correlates well with the internal angle defined by the 2- and 5 substituents and the centers of the furan (14) or thiophene (20) subunits.

[Structure: see text] Unique core-modified porphyrinoids, such as oxabenziporphyrins, oxapyriporphyrins, and thiapyriporphyrins, bearing exocyclic C-C double bonds at meso-positions, have been synthesized and characterized. The synthesis was accomplished by utilizing typical "3+1"-type condensation. Two different stable tautomeric forms were isolated, and the two tautomeric forms can be interconvertible upon treatment with base. In contrast, only the structure bearing an exocyclic double bond was isolated in the case of oxapyriporphyrin and oxabenziporphyrin.

We developed a new synthetic method for bicyclo[2.2.2]octadiene (BCOD)-fused porphyrin (1), a tetrabenzoporphyrin (TBP, 2) precursor that is well-known as a good material for use in organic electronic devices. The newly developed method synthesizes the BCOD-fused pyrrole intermediate (which is the most important intermediate in synthesizing BCOD-fused porphyrin) in a simpler and easier manner than other existing methods, and thus, the new method can efficiently synthesize the TBP precursor.