SYNTHESIS OF SUBSTITUTED CARBAPORPHRYINS FROM CARBATRYPYRRINS
Carbaporphyrins are porphyrin analogues in which one of the core nitrogen atoms has been replaced by carbon. These aromatic macrocycles have intriguing reactivity and readily form organometallic derivatives. Recently, a new route to carbaporphyrins was developed starting from indene and pyrrole-2-carbaldehyde 1a. Technical grade indene and 1a were refluxed in ethanol with KOH to give fulvene 2a. Subsequent reduction with LiAlH4 afforded a related dihydrofulvene and this reacted with 1a under basic conditions to generate carbatripyrrin 3a. This key intermediate was used to prepare a series of carbaporphyrins 4 and hetero-analogues incorporating furan, thiophene and selenophene rings. However, this strategy afforded porphyrinoids with poor solubility characteristics, limiting applications for further studies. In order to overcome this deficiency, dimethyl substituted pyrrole aldehyde 1b has been used to explore the carbatripyrrin methodology. Hence, condensation of dimethylpyrrole aldehyde 1b with indene affords fulvene 2b, and further reaction with lithium aluminum hydride generated a substituted dihydroindene. The utility of this intermediate in preparing new carbaporphyrin structures is currently under investigation.
Woods, John, "SYNTHESIS OF SUBSTITUTED CARBAPORPHRYINS FROM CARBATRYPYRRINS" (2019). University Research Symposium. 304.